Aviation Glossary

Term Definition
Aborted takeoff A takeoff that is terminated prematurely when it is determined that some condition exists that makes takeoff or further flight dangerous.
Absolute pressure regulator A valve used in a pneumatic system at the pump inlet to regulate the compressor inlet air pressure to prevent excessive speed variation and/or overspeeding of the compressor.
Absolute zero The point at which all molecular motion ceases. Absolute zero is -460 °F and -273 °C
Accumulator A hydraulic component that consists of two compartments separated by a movable component, such as a piston, diaphragm, or bladder. One compartment is filled with compressed air or nitrogen, and the other is filled with hydraulic fluid and is connected into the system pressure manifold. An accumulator allows an incompressible fluid to be stored under pressure by the force produced by a compressible fluid. Its primary purposes are to act as a shock absorber in the system, and to provide a source of additional hydraulic power when heavy demands are placed on the system
Actuator A fluid power device that changes fluid pressure into mechanical motion.
Advancing blade The blade on a helicopter rotor whose tip is moving in the same direction the helicopter is moving.
Aerodynamic drag The total resistance to the movement of an object through the air. Aerodynamic drag is composed of both induced drag and parasite drag. See induced drag and parasite drag
Aerodynamic lift The force produced by air moving over a specially shaped surface called an airfoil. Aerodynamic lift acts in a direction perpendicular to the direction the air is moving
Aeroelastic tailoring The design of an aerodynamic surface whose strength and stiffness are matched to the aerodynamic loads that will be imposed upon it.
Aeronautical Radio Incorporated (ARINC) A corporation whose principal stockholders are the airlines. Its function is to operate certain communication links between airliners in flight and the airline ground facilities. ARINC also sets standards for communication equipment used by the airlines
Aging A change in the characteristics of a material with time. Certain aluminum alloys do not have their full strength when they are first removed from the quench bath after they have been heat-treated, but they gain this strength after a few days by the natural process of aging
Air carrier An organization or person involved in the business of transporting people or cargo by air for compensation or hire.
Air-cycle cooling system A system for cooling the air in the cabin of a turbojet-powered aircraft. Compressor bleed air passes through two heat exchangers where it gives up some of its heat; then, it drives an expansion turbine where it loses still more of its heat energy as the turbine drives a compressor. When the air leaves the turbine, it expands and its pressure and temperature are both low
Aircraft communication addressing and reporting system (ACARS) A two-way communication link between an airliner in flight and the airline's main ground facilities. Data is collected in the aircraft by digital sensors and is transmitted to the ground facilities. Replies from the ground may be printed out so the appropriate flight crewmember can have a hard copy of the response
Airworthiness Alert A notice sent by the FAA to certain interested maintenance personnel identifying problems with aircraft that have been gathered from Malfunction and Defect Reports. These problems are being studied at the time the Airworthiness Alert is issued but have not been fully evaluated by the time the material went to press
Airworthiness Directive A notice sent out by the Transport Canada (TC) to the registered owner of an aircraft notifying him or her of an unsafe condition that has been found on the aircraft. Compliance with AD notes is mandatory
Alclad A registered trade name for clad aluminum alloy.
Alodine The registered trade name for a popular conversion coating chemical used to produce a hard, airtight, oxide film on aluminum alloy for corrosion protection.
Alphanumeric symbols Symbols made up of all of the letters in our alphabet, numerals, punctuation marks, and certain other special symbols.
Alternator An electrical generator that produces alternating current. The popular DC alternator used on light aircraft produces three-phase AC in its stator windings. This AC is changed into DC by a six-diode, solid-state rectifier before it leaves the alternator
Alumel An alloy of nickel, aluminum, manganese, and silicon that is the negative element in a thermocouple used to measure exhaust gas temperature.
American wire gauge The system of measurement of wire size used in aircraft electrical systems.
Amphibian An airplane with landing gear that allows it to operate from both water and land surfaces.
Amplifier An electronic circuit in which a small change in voltage or current controls a much larger change in voltage or current.
Analog electronics Electronics in which values change in a linear fashion. Output values vary in direct relationship to changes of input values
Analog-type indicator An electrical meter that indicates values by the amount a pointer moves across a graduated numerical scale.
Aneroid The sensitive component in an altimeter or barometer that measures the absolute pressure of the air. The aneroid is a sealed, flat capsule made of thin corrugated disks of metal soldered together and evacuated by pumping all of the air out of it. Evacuating the aneroid allows it to expand or collapse as the air pressure on the outside changes
Angle of attack The acute angle formed between the chord line of an airfoil and the direction of the air that strikes the airfoil.
Angle of attack indicator An instrument that measures the angle between the local airflow around the direction detector and the fuselage reference plane.
Angle of incidence The acute angle formed between the chord line of an airfoil and the longitudinal axis of the aircraft on which it is mounted.
Annual rings The rings that appear in the end of a log cut from a tree. The number of annual rings per inch gives an indication of the strength of the wood. The more rings there are and the closer they are together, the stronger the wood. The pattern of alternating light and dark rings is caused by the seasonal variations in the growth rate of the tree. A tree grows quickly in the spring and produces the light-colored, less dense rings. The slower growth during the summer, or latter part of the growing season, produces the dark-colored, denser rings
Annunciator panel A panel of warning lights in plain sight of the pilot. These lights are identified by the name of the system they represent and are usually covered with colored lenses to show the meaning of the condition they announce
Anodizing The electrolytic process in which a hard, airtight, oxide film is deposited on aluminum alloy for corrosion protection.
Antenna A special device used with electronic communication and navigation systems to radiate and receive electromagnetic energy.
Anti-icer system A system that prevents the formation of ice on an aircraft structure.
Anti-icing additive A chemical added to the turbine-engine fuel used in some aircraft. This additive mixes with water that condenses from the fuel and lowers its freezing temperature so it will not freeze and block the fuel filters. It also acts as a biocidal agent and prevents the formation of microbial contamination in the tanks
Antidrag wire A structural wire inside a Pratt truss airplane wing between the spars. Antidrag wires run from the rear spar inboard, to the front spar at the next bay outboard. Antidrag wires oppose the forces that try to pull the wing forward
Antiservo tab A tab installed on the trailing edge of a stabilator to make it less sensitive. The tab automatically moves in the same direction as the stabilator to produce an aerodynamic force that tries to bring the surface back to a streamline position. This tab is also called an antibalance tab
Antiskid brake system An electrohydraulic system in an airplane's power brake system that senses the deceleration rate of every main landing gear wheel. If any wheel decelerates too rapidly, indicating an impending skid, pressure to that bake is released and the wheel stops decelerating. Pressure is then reapplied at a slightly lower value
Antitear strip Strips of aircraft fabric laid under the reinforcing tape before the fabric is stitched to an aircraft wing.
Arbor press A press with either a mechanically or hydraulically operated ram used in a maintenance shop for a variety of pressing functions.
Arcing Sparking between a commutator and brush or between switch contacts that is caused by induced current when a circuit is broken.
Area The number of square units in a surface.
Aspect ratio The ratio of the length, or span, of an airplane wing to its width, or chord. For a nonrectangular wing, the aspect ratio is found by dividing the square of the span of the wing by its area. Aspect Ratio = span2 -: area
Asymmetrical airfoil An airfoil section that is not the same on both sides of the chord line.
Asymmetrical lift A condition of uneven lift produced by the rotor when a helicopter is in forward flight. Asymmetrical lift is caused by the difference between the airspeed of the advancing blade and that of the retreating blade
Attenuate To weaken, or lessen the intensity of, an activity.
Attitude indicator A gyroscopic flight instrument that gives the pilot an indication of the attitude of the aircraft relative to its pitch and roll axes. The attitude indicator in an autopilot is in the sensing system that detects deviation from a level- flight attitude
Augmenter tube A long, stainless steel tube around the discharge of the exhaust pipes of a reciprocating engine. Exhaust gases flow through the augmenter tube and produce a low pressure that pulls additional cooling air through the engine compartment. Heat may be taken from the augmenter tubes and directed through the leading edges of the wings for thermal anti-icing
Autoclave A pressure vessel inside of which air can be heated to a high temperature and pressure raised to a high value. Autoclaves are used in the composite manufacturing industry to apply heat and pressure for curing resins
Autogiro A heavier-than-air rotor-wing aircraft sustained in the air by rotors turned by aerodynamic forces rather than by engine power. When the name Autogiro is spelled with a capital A, it refers to a specific series of machines built by Juan de la Cierva or his successors
Autoignition system A system on a turbine engine that automatically energizes the igniters to provide a relight if the engine should flame out.
Automatic adjuster A subsystem in an aircraft disk brake that compensates for disk or lining wear. Each time the brakes are applied, the automatic adjuster is reset for zero clearance, and when the brakes are released, the clearance between the disks or the disk and lining is returned to a preset value. A malfunctioning automatic adjuster in a multiple-disk brake can cause sluggish and jerky operation
Automatic flight control system (AFCS) The full system of automatic flight control that includes the autopilot, flight director, horizontal situation indicator, air data sensors, and other avionics inputs.
Autorotation Descent of a helicopter without the use of engine power. An aerodynamic force causes the rotors to rotate
Autosyn system A synchro system used in remote indicating instruments. The rotors in an Autosyn system are two-pole electromagnets, and the stators are delta-connected, three-phase, distributed-pole windings in the stator housings. The rotors in the transmitters and indicators are connected in parallel and are excited with 26-volt, 400-Hz AC. The rotor in the indicator follows the movement of the rotor in the transmitter
Auxiliary power unit (APU) A small turbine or reciprocating engine that drives a generator, hydraulic pump, and air pump. The APU is installed in the aircraft and is used to supply electrical power, compressed air, and hydraulic pressure when the main engines are not running
Aviation snips Compound-action hand shears used for cutting sheet metal. Aviation snips come in sets of three. One pair cuts to the left, one pair cuts to the right, and the third pair of snips cuts straight
Aviator's oxygen Oxygen that has had almost all of the water and water vapor removed from it.
Avionics The branch of technology that deals with the design, production, installation, use, and servicing of electronic equipment mounted in aircraft.
Azimuth A horizontal angular distance, measured clockwise from a fixed reference direction to an object.
Backhand welding Welding in which the torch is pointed away from the direction the weld is progressing.
Backplate (brake component) A floating plate on which the wheel cylinder and the brake shoes attach on an energizing- type brake.
Backup ring A flat leather or Teflon ring installed in the groove in which an O-ring or T-seal is placed. The backup ring is on the side of the seal away from the pressure, and it prevents the pressure extruding the seal between the piston and the cylinder wall
Balance cable A cable in the aileron system of an airplane that connects to one side of each aileron. When the control wheel is rotated, a cable from the cockpit pulls one aileron down and relaxes the cable going to the other aileron. The balance cable pulls the other aileron up
Balance panel A flat panel hinged to the leading edge of some ailerons that produces a force which assists the pilot in holding the ailerons deflected. The balance panel divides a chamber ahead of the aileron in such a way that when the aileron is deflected downward, for example, air flowing over its top surface produces a low pressure that acts on the balance panel and causes it to apply an upward force to the aileron leading edge
Balance tab An adjustable tab mounted on the trailing edge of a control surface to produce a force that aids the pilot in moving the surface. The tab is automatically actuated in such a way it moves in the direction opposite to the direction the control surface on which it is mounted moves
Balanced actuator A linear hydraulic or pneumatic actuator that has the same area on each side of the piston.
Banana oil Nitrocellulose dissolved in amyl acetate, so named because it smells like bananas.
Bank (verb) The act of rotating an aircraft about its longitudinal axis.
Barometric scale A small window in the dial of a sensitive altimeter in which the pilot sets the barometric pressure level from which the altitude shown on the altimeter is measured. This window is sometimes called the "Kollsman" window base. The electrode of a bipolar transistor between the emitter and the collector. Varying a small flow of electrons moving into or out of the base controls a much larger flow of electron between the emitter and the collector
Base The electrode of a bipolar transistor between the emitter and the collector. Varying a small flow of electrons moving into or out of the base controls a much larger flow of electrons between the emitter and the collector
Bead (tire component) The high-strength carbon-steel wire bundles that give an aircraft tire its strength and stiffness where it mounts on the wheel.
Bead seat area The flat surface on the inside of the rim of an aircraft wheel on which the bead of the tire seats.
Bearing strength (sheet metal characteristic) The amount of pull needed to cause a piece of sheet metal to tear at the points at which it is held together with rivets. The bearing strength of a material is affected by both its thickness and the diameter of the rivet
Beehive spring A hardened-steel, coil-spring retainer used to hold a rivet set in a pneumatic rivet gun. This spring gets its name from its shape. It screws onto the end of the rivet gun and allows the set to move back and forth, but prevents it being driven from the gun
Bend allowance The amount of material actually used to make a bend in a piece of sheet metal. Bend allowance depends upon the thickness of the metal and the radius of the bend, and is normally found in a bend allowance chart
Bend radius The radius of the inside of a bend.
Bend tangent line A line made in a sheet metal layout that indicates the point at which the bend starts.
Bernoulli's principle The basic principle that explains the relation between kinetic energy and potential energy in fluids that are in motion. When the total energy in a column of moving fluid remains constant, any increase in the kinetic energy of the fluid (its velocity) results in a corresponding decrease in its potential energy (its pressure)
Bezel The rim that holds the glass cover in the case of an aircraft instrument.
Bias-cut surface tape A fabric tape in which the threads run at an angle of 45° to the length of the tape. Bias-cut tape may be stretched around a compound curve such as a wing tip bow without wrinkling
Bilge area A low portion in an aircraft structure in which water and contaminants collect. The area under the cabin floorboards is normally called the bilge
Bipolar transistor A solid-state component in which the flow of current between its emitter and collector is controlled by a much smaller flow of current into or out of its base. Bipolar transistors may be of either the NPN or PNP type
BITE Built-in test equipment.
Blade track The condition of a helicopter rotor in which each blade follows the exact same path as the blade ahead of it.
Black box A term used for any portion of an electrical or electronic system that can be removed as a unit. A black box does not have to be a physical box
Bladder-type fuel cell A plastic-impregnated fabric bag supported in a portion of an aircraft structure so that it forms a cell in which fuel is carried.
Bleeder A material such as glass cloth or mat that is placed over a composite lay-up to absorb the excess resin forced out of the ply fibers when pressure is applied.
Bleeding dope Dope whose pigments are soluble in the solvents or thinners used in the finishing system. The color will bleed up through the finished coats
Bleeding of brakes The maintenance procedure of removing air entrapped in hydraulic fluid in the brakes. Fluid is bled from the brake system until fluid with no bubbles flows out
Blimp A cigar-shaped, nonrigid lighter-than-air flying machine.
Blush A defect in a lacquer or dope finish caused by moisture condensing on the surface before the finish dries. If the humidity of the air is high, the evaporation of the solvents cools the air enough to cause the moisture to condense. The water condensed from the air mixes with the lacquer or dope and forms a dull, porous, chalky-looking finish called blush. A blushed finish is neither attractive nor protective
Bonding The process of electrically connecting all isolated components to the aircraft structure. Bonding provides a path for return current from electrical components, and a low-impedance path to ground to minimize static electrical charges. Shock-mounted components have bonding braids connected across the shock mounts
Boost pump An electrically driven centrifugal pump mounted in the bottom of the fuel tanks in large aircraft. Boost pumps provide a positive flow of fuel under pressure to the engine for starting and serve as an emergency backup in the event an engine-driven pump should fail. They are also used to transfer fuel from one tank to another and to pump fuel overboard when it is being dumped. Boost pumps prevent vapor locks by holding pressure on the fuel in the line to the engine-driven pump. Centrifugal boost pumps have a small agitator propeller on top of the impeller to force vapors from the fuel before it leaves the tank
Boundary layer The layer of air that flows next to an aerodynamic surface. Because of the design of the surface and local surface roughness, the boundary layer often has a random flow pattern, sometimes even flowing in a direction opposite to the direction of flight. A turbulent boundary layer causes a great deal of aerodynamic drag
Bourdon tube A pressure-indicating mechanism used in most oil pressure and hydraulic pressure gages. It consists of a sealed, curved tube with an elliptical cross section. Pressure inside the tube tries to straighten it, and as it straightens, it moves a pointer across a calibrated dial. Bourdon-tube pressure gauges are used to measure temperature by measuring the vapor pressure in a sealed container of a volatile liquid, such as methyl chloride, whose vapor pressure varies directly with its temperature
Brazing A method of thermally joining metal parts by wetting the surface with a molten nonferrous alloy. When the molten material cools and solidifies, it holds the pieces together. Brazing materials melt at a temperature higher than 800 °F, but lower than the melting temperature of the metal on which they are used
British thermal unit (BTU) The amount of heat energy needed to raise the temperature of one pound of pure water l °F.
Bucking bar A heavy steel bar with smooth, hardened surfaces, or faces. The bucking bar is held against the end of the rivet shank when it is driven with a pneumatic rivet gun, and the shop head is formed against the bucking bar
Buffeting Turbulent movement of the air over an aerodynamic surface.
Bulb angle An L-shaped metal extrusion having an enlarged, rounded edge that resembles a bulb on one of its legs.
Bulkhead A structural partition that divides the fuselage of an aircraft into compartments, or bays.
Bungee shock cord A cushioning material used with the nonshock absorbing landing gears installed on older aircraft. Bungee cord is made up of many small rubber bands encased in a loose-woven cotton braid
Burnish (verb) To smooth the surface of metal that has been damaged by a deep scratch or gouge. The metal piled up at the edge of the damage is pushed back into the damage with a smooth, hard steel burnishing tool
Burr A sharp rough edge of a piece of metal left when the metal was sheared, punched, or drilled.
Bus A point within an electrical system from which the individual circuits get their power.
Buttock line A line used to locate a position to the right or left of the center line of an aircraft structure.
Butyl Trade name for a synthetic rubber product made by the polymerization of isobutylene. Butyl withstands such potent chemicals as phosphate ester-base (Skydrol) hydraulic fluids
Cage (verb) To lock the gimbals of a gyroscopic instrument so it will not be damaged by abrupt flight maneuvers or rough handling.
Calendar month A measurement of time used by the FAA for inspection and certification purposes. One calendar month from a given day extends from that day until midnight of the last day of that month
Calender (fabric treatment) To pass fabric through a series of heated rollers to give it a smooth shiny surface.
Calorie The amount of heat energy needed to raise the temperature of one gram of pure water l °C.
Canted rate gyro A rate gyro whose gimbal axis is tilted so it can sense rotation of the aircraft about its roll axis as well as its yaw axis.
Camber (wheel alignment) The amount the wheels of an aircraft are tilted, or inclined, from the vertical. If the top of the wheel tilts outward, the camber is positive. If the top of the wheel tilts inward, the camber is negative
Cantilever wing A wing that is supported by its internal structure and requires no external supports. The wing spars are built in such a way that they carry all the bending and torsional loads
Cap strip The main top and bottom members of a wing rib. The cap strips give the rib its aerodynamic shape
Capacitance-type fuel quantity measuring system A popular type of electronic fuel quantity indicating system that has no moving parts in the fuel tank. The tank units are cylindrical capacitors, called probes, mounted across the tank, from top to bottom. The dielectric between the plates of the probes is either fuel or the air above the fuel, and the capacitance of the probe varies with the amount of fuel in the tank. The indicator is a servo-type instrument driven by the amplified output of a capacitance bridge
Capillary tube A soft copper tube with a small inside diameter. The capillary tube used with vapor-pressure thermometer connects the temperature sensing bulb to the Bourdon tube. The capillary tube is protected from physical damage by enclosing it in a braided metal wire jacket
Carbon monoxide detector A packet of chemical crystals mounted in the aircraft cockpit or cabin where they are easily visible. The crystals change their color from yellow to green when they are exposed to carbon monoxide
Carbon-pile voltage regulator A type of voltage regulator used with high-output DC generators. Field current is controlled by varying the resistance of a stack of thin carbon disks. This resistance is varied by controlling the amount the stack is compressed by a spring whose force is opposed by the pull of an electromagnet. The electromagnet's strength is proportional to the generator's output voltage
Carburizing flame An oxyacetylene flame produced by an excess of acetylene. This flame is identified by a feather around the inner cone. A carburizing flame is also called a reducing flame
Carcass (tire component) The layers of rubberized fabric that make up the body of an aircraft tire.
Case pressure A low pressure that is maintained inside the case of a hydraulic pump. If a seal becomes damaged, hydraulic fluid will be forced out of the pump rather than allowing air to be drawn into the pump
Cathode-ray tube (CRT) A display tube used for oscilloscopes and computer video displays. An electron gun emits a stream of electrons that is attracted to a positively charged inner surface of the face of the tube. Acceleration and focusing grids speed the movement of the electrons and shape the beam into a pinpoint size. Electrostatic or electromagnetic forces caused by deflection plates or coils move the beam over the face of the tube. The inside surface of the face of the tube is treated with a phosphor material that emits light when the beam of electrons strikes it
Cavitation A condition that exist in a hydraulic pump when there is not enough pressure in the reservoir to force fluid to the inlet of the pump. The pump picks up air instead of fluid
CDI See Course deviation indicator.
CDU See Control display unit.
Center of lift The location of the chord line of an airfoil at which all the lift forces produced by the airfoil are considered to be concentrated.
Center of pressure The point on the chord line of an airfoil where all of the aerodynamic forces are considered to be concentrated.
Centering cam A cam in the nose-gear shock strut that causes the piston to center when the strut fully extends. When the aircraft takes off and the strut extends, the wheel is straightened in its fore-and-aft position so it can be retracted into the wheel well
Charging stand (air conditioning service equipment) A handy and compact arrangement of air conditioning servicing equipment. A charging stand contains a vacuum pump, a manifold gauge set, and a method of measuring and dispensing the refrigerant
Chatter A type of rapid vibration of a hydraulic pump caused by the pump taking in some air along with the hydraulic fluid.
Check (wood defect) Longitudinal cracks that extend across a log's annual rings.
Check valve A hydraulic or pneumatic system component that allows full flow of fluid in one direction but blocks all flow in the opposite direction.
Chemical oxygen candle system An oxygen system used for emergency or backup use. Solid blocks of material that release oxygen when they are burned are carried in special fireproof fixtures. When oxygen is needed, the candles are ignited with an integral igniter, and oxygen flows into the tubing leading to the masks
Chevron seal A form of one-way seal used in some fluid- power actuators. A chevron seal is made of a resilient material whose cross section is in the shape of the letter V. The pressure being sealed must be applied to the open side of the V
Chromel An alloy of nickel and chromium used as the positive element in a thermocouple for measuring exhaust gas temperature.
Circle A closed plane figure with every point an equal distance from the center. A circle has the greatest area for its circumference of any enclosed shape
Circuit breaker An electrical component that automatically opens a circuit any time excessive current flows through it. A circuit breaker may be reset to restore the circuit after the fault causing the excessive current has been corrected
Clad aluminum A sheet of aluminum alloy that has a coating of pure aluminum rolled on one or both of its surfaces for corrosion protection.
Clamp-on ammeter An electrical instrument used to measure current without opening the circuit through which it is flowing. The jaws of the ammeter are opened, slipped over the current- carrying wire, and then clamped shut. Current flowing through the wire produces a magnetic field which induces a voltage in the ammeter that is proportional to the amount of current
Cleco fastener A patented spring-type fastener used to hold metal sheets in position until they can be permanently riveted together.
Close-quarter iron A small hand-held iron with an accurately calibrated thermostat. This iron is used for heat- shrinking polyester fabrics in areas that would be difficult to work with a large iron
Closed angle An angle formed in sheet metal that has been bent more than 90°.
Closed assembly time The time elapsing between the assembly of glued joints and the application of pressure.
Closed-center hydraulic system A hydraulic system in which the selector valves are installed in parallel with each other. When no unit is actuated, fluid circulates from the pump back to the reservoir without flowing through any of the selector valves
Closed-center selector valve A type of flow-control valve used to direct pressurized fluid into one side of an actuator, and at the same time, direct the return fluid from the other side of the actuator to the fluid reservoir. Closed-center selector valves are connected in parallel between the pressure manifold and the return manifold
Coaxial Rotating about the same axis. Coaxial rotors of a helicopter are mounted on concentric shafts in such a way that they turn in opposite directions to cancel torque
Coaxial cable A special type of electrical cable that consists of a central conductor held rigidly in the center of a braided outer conductor. Coaxial cable, commonly called coax, is used for attaching radio receivers and transmitters to their antenna
Coefficient of drag A dimensionless number used in the formula for determining induced drag as it relates to the angle of attack.
Coefficient of lift A dimensionless number relating to the angle of attack used in the formula for determining aerodynamic lift.
Coin dimpling A process of preparing a hole in sheet metal for flush riveting. A coining die is pressed into the rivet hole to form a sharp-edged depression into which the rivet head fits
Collective pitch control The helicopter control that changes the pitch of all of the rotor blades at the same time. Movement of the collective pitch control increases or decreases the lift produced by the entire rotor disk
Collodion Cellulose nitrate used as a film base for certain aircraft dopes.
Combustion heater A type of cabin heater used in some aircraft. Gasoline from the aircraft fuel tanks is burned in the heater
Compass fluid A highly refined, water-clear petroleum product similar to kerosene. Compass fluid is used to dampen the oscillations of magnetic compasses
Compass rose A location on an airport where an aircraft can be taken to have its compasses "swung." Lines are painted on the rose to mark the magnetic directions in 30° increments
Compass swinging A maintenance procedure that minimizes deviation error in a magnetic compass. The aircraft is aligned on a compass rose, and the compensating magnets in the compass case are adjusted so the compass card indicates the direction marked on the rose. After the deviation error is minimized on all headings, a compass correction card is completed and mounted on the instrument panel next to the compass
Compensated fuel pump A vane-type, engine-driven fuel pump that has a diaphragm connected to the pressure regulating valve. The chamber above the diaphragm is vented to the carburetor upper deck where it senses the pressure of the air as it enters the engine. The diaphragm allows the fuel pump to compensate for altitude changes and keeps the carburetor inlet fuel pressure a constant amount higher than the carburetor inlet air pressure
Compensator port (brake system component) A small hole between a hydraulic brake master cylinder and the reservoir. When the brakes are released, this port is uncovered and the fluid in the master cylinder is vented to the reservoir. When the brake is applied, the master-cylinder piston covers the compensator port and allows pressure in the line to the brake to build up and apply the brakes. When the brake is released, the piston uncovers the compensator port. If any fluid has been lost from the brake, the reservoir will refill the master cylinder. A restricted compensator port will cause the brakes to drag or will cause them to be slow to release
Composite Something made up of different materials combined in such a way that the characteristics of the resulting material are different from those of any of the components.
Compound curve A curve formed in more than one plane. The surface of a sphere is a compound curve
Compound gauge (air conditioning servicing equipment) A pressure gauge used to measure the pressure in the low side of an air conditioning system. A compound gauge is calibrated from zero to 30 inches of mercury vacuum, and from zero to about l50-psi positive gauge pressure
Compressibility effect The sudden increase in the total drag of an airfoil in transonic flight caused by formation of shock waves on the surface.
Compression failure A type of structural failure in wood caused by the application of too great a compressive load. A compression failure shows up as a faint line running at right angles to the grain of the wood
Compression strut A heavy structural member, often in the form of a steel tube, used to hold the spars of a Pratt truss airplane wing apart. A compression strut opposes the compressive loads between the spars arising from the tensile loads produced by the drag and antidrag wires
Compression wood A defect in wood that causes it to have a high specific gravity and the appearance of an excessive growth of summerwood. In most species, there is little difference between the color of the springwood and the summerwood. Any material containing compression wood is unsuited for aircraft structural use and must be rejected
Compressor (air conditioning system component) The component in a vapor-cycle cooling system in which the low-pressure refrigerant vapors, after they leave the evaporator, are compressed to increase both their temperature and pressure before they pass into the condenser. Some compressors are driven by electric motors, others by hydraulic motors and, in the case of most light airplanes, are belt driven from the engine
Concave surface A surface that is curved inward. The outer edges are higher than the center
Condenser (air conditioning system component) The component in a vapor-cycle cooling system in which the heat taken from the aircraft cabin is given up to the ambient air outside the aircraft.
Conductor (electrical) A material that allows electrons to move freely from one atom to another within the material.
Coning angle The angle formed between the plane of rotation of a helicopter rotor blade when it is producing lift and a line perpendicular to the rotor shaft. The degree of the coning angle is determined by the relationship between the centrifugal force acting on the blades and the aerodynamic lift produced by the blades
Constant (mathematical) A value used in a mathematical computation that is the same every time it is used. For example, the relationship between the length of the circumference of a circle and the length of its diameter is a constant, 3.l4l6. This constant is called by the Greek name of Pi (7r)
Constant differential mode (cabin pressurization) The mode of pressurization in which the cabin pressure is maintained a constant amount higher than the outside air pressure. The maximum differential pressure is determined by the structural strength of the aircraft cabin
Constant-displacement pump A fluid pump that moves a specific volume of fluid each time it rotates; the faster the pump turns, the more fluid it moves. Some form of pressure regulator or relief valve must be used with a constant- displacement pump when it is driven by an aircraft engine
Constant-speed drive (CSD) A special drive system used to connect an alternating current generator to an aircraft engine. The drive holds the generator speed (and thus its frequency) constant as the engine speed varies
Constantan A copper-nickel alloy used as the negative lead of a thermocouple for measuring the cylinder head temperature of a reciprocating engine.
Contactor (electrical component) A remotely actuated, heavy-duty electrical switch. Contactors are used in an aircraft electrical system to connect the battery to the main bus
Continuity tester A troubleshooting tool that consists of a battery, a light bulb, and test leads. The test leads are connected to each end of the conductor under test, and if the bulb lights up, there is continuity. If it does not light up, the conductor is open
Continuous Airworthiness Inspection Program An inspection program that is part of a continuous airworthiness maintenance program approved for certain large airplanes (to which l4 CFR Part l25 is not applicable), turbojet multi-engine airplanes, turbopropeller-powered multi-engine airplanes, and turbine-powered rotorcraft.
Continuous-duty solenoid A solenoid-type switch designed to be kept energized by current flowing through its coil for an indefinite period of time. The battery contactor in an aircraft electrical system is a continuous-duty solenoid. Current flows through its coil all the time the battery is connected to the electrical system
Continuous-flow oxygen system A type of oxygen system that allows a metered amount of oxygen to continuously flow into the mask. A rebreather-type mask is used with a continuous-flow system. The simplest form of continuous- flow oxygen system regulates the flow by a calibrated orifice in the outlet to the mask, but most systems use either a manual or automatic regulator to vary the pressure across the orifice proportional to the altitude being flown
Continuous-loop fire-detection system A fire-detection system that uses a continuous loop of two conductors separated with a thermistor-type insulation. Under normal temperature conditions, the thermistor material is an insulator; but if it is exposed to a fire, the thermistor changes into a conductor and completes the circuit between the two conductors, initiating a fire warning
Control horn The arm on a control surface to which the control cable or push-pull rod attaches to move the surface.
Control stick The type of control device used in some airplanes. A vertical stick in the flight deck controls the ailerons by side-to-side movement and the elevators by fore- and-aft movement
Control yoke The movable column on which an airplane control wheel is mounted. The yoke may be moved in or out to actuate the elevators, and the control wheel may be rotated to actuate the ailerons
Conventional current An imaginary flow of electricity that is said to flow from the positive terminal of a power source, through the external circuit to its negative terminal. The arrowheads in semiconductor symbols point in the direction of conventional current flow
Converging duct A duct, or passage, whose cross-sectional area decreases in the direction of fluid flow.
Conversion coating A chemical solution used to form an airtight oxide or phosphate film on the surface of aluminum or magnesium parts. The conversion coating prevents air from reaching the metal and keeps it from corroding
Convex surface A surface that is curved outward. The outer edges are lower than the center
Coriolis effect The change in rotor blade velocity to compensate for a change in the distance between the center of mass of the rotor blade and the axis rotation of the blade as the blades flap in flight.
Cornice brake A large shop tool used to make straight bends across a sheet of metal. Cornice brakes are often called leaf brakes
Corrugated metal Sheets of metal that have been made more rigid by forming a series of parallel ridges or waves in its surface.
Cotter pin A split metal pin used to safety a castellated or slotted nut on a bolt. The pin is passed through the hole in the shank of the bolt and the slots in the nut, and the ends of the pin are spread to prevent it backing out of the hole
Countersinking Preparation of a rivet hole for a flush rivet by beveling the edges of the holes with a cutter of the correct angle.
Coverite surface thermometer A small surface-type bimetallic thermometer that calibrates the temperature of an iron used to heat-shrink polyester fabrics.
Crabbing Pointing the nose of an aircraft into the wind to compensate for wind drift.
Crazing A form of stress-caused damage that occurs in a transparent thermoplastic material. Crazing appears as a series of tiny, hair-like cracks just below the surface of the plastic
Critical Mach number The flight Mach number at which there is the first indication of supersonic airflow over any part of the aircraft structure.
Cross coat A double coat of aircraft finishing material in which the second coat is sprayed at right angles to the first coat, before the solvents have evaporated from the first coat.
Cross-feed valve (fuel system component) A valve in a fuel system that allows any of the engines of a multi-engine aircraft to draw fuel from any fuel tank. Cross-feed systems are used to allow a multi-engine aircraft to maintain a balanced fuel condition
Cross-flow valve An automatic flow-control valve installed between the gear-up and gear-down lines of the landing gear of some large airplanes. When the landing gear is released from its uplocks, its weight causes it to fall faster than the hydraulic system can supply fluid to the gear-down side of the actuation cylinder. The cross-flow valve opens and directs fluid from the gear-up side into the gear-down side. This allows the gear to move down with a smooth motion
CRT See Cathode-ray tube.
Cryogenic liquid A liquid which boils at temperatures of less than about ll0 °F (--l63 °C) at normal atmospheric pressures.
Cuno filter The registered trade name for a particular style of edge-type fluid filter. Cuno filters are made up of a stack of thin metal disks that are separated by thin scraper blades. Contaminants collect on the edge of the disks, and they are periodically scraped out and allowed to collect in the bottom of the filter case for future removal
Current A general term used for electrical flow. See conventional current
Current limiter An electrical component used to limit the amount of current a generator can produce. Some current limiters are a type of slow-blow fuse in the generator output. Other current limiters reduce the generator output voltage if the generator tries to put out more than its rated current
Cusp A pointed end.
Cyclic pitch control The helicopter control that allows the pilot to change the pitch of the rotor blades individually, at a specific point in their rotation. The cyclic pitch control allows the pilot to tilt the plane of rotation of the rotor disk to change the direction of lift produced by the rotor
Dacron The registered trade name for a cloth woven from polyester fibers.
Damped oscillation Oscillation whose amplitude decreases with time.
Database A body of information that is available on any particular subject.
Data bus A wire or group of wires that are used to move data within a computer system.
Debooster valve A valve in a power brake system between the power brake control valve and the wheel cylinder. This valve lowers the pressure of the fluid going to the brake and increases its volume. A debooster valve increases the smoothness of brake application and aids in rapid release of the brakes
Decay The breakdown of the structure of wood fibers. Wood that shows any indication of decay must be rejected for use in aircraft structure
Decomposition The breakdown of the structure of wood fibers. Wood that shows any indication of decay must be rejected for use in aircraft structure
Deciduous A type of tree that sheds its foliage at the end of the growing season. Hardwoods come from deciduous trees
Dedicated computer A small digital computer, often built into an instrument or control device that contains a built-in program that causes it to perform a specific function.
Deep-vacuum pump A vacuum pump capable of removing almost all of the air from a refrigeration system. A deep- vacuum pump can reduce the pressure inside the system to a few microns of pressure
Deflator cap A cap for a tire, strut, or accumulator air valve that, when screwed onto the valve, depresses the valve stem and allows the air to escape safely through a hole in the side of the cap.
Deicer system A system that removes ice after it has formed on an aircraft.
Delamination The separation of the layers of a laminated material.
Delivery air duct check valve An isolation valve at the discharge side of the air turbine that prevents the loss of pressurization through a disengaged cabin air compressor.
Delta airplane An airplane with a triangular-shaped wing. This wing has an extreme amount of sweepback on its leading edge, and a trailing edge that is almost perpendicular to the longitudinal axis of the airplane
Delta connection (electrical connection) A method of connecting three electrical coils into a ring or, as they are drawn on a schematic diagram as a triangle, a delta (D).
Denier A measure of the fineness of the yarns in a fabric.
Density ratio (O) The ratio of the density of the air at a given altitude to the density of the air at sea level under standard conditions.
Derated (electrical specification) Reduction in the rated voltage or current of an electrical component. Derating is done to extend the life or reliability of the device
Desiccant (air conditioning component) A drying agent used in an air conditioning system to remove water from the refrigerant. A desiccant is made of silica-gel or some similar material
Detent A spring-loaded pin or tab that enters a hole or groove when the device to which it is attached is in a certain position. Detents are used on a fuel valve to provide a positive means of identifying the fully on and fully off position of the valve
Detonation An explosion, or uncontrolled burning of the fuel-air mixture inside the cylinder of a reciprocating engine. Detonation occurs when the pressure and the temperature inside the cylinder become higher than the critical pressure and temperature of the fuel. Detonation is often confused with preignition
Deviation error An error in a magnetic compass caused by localized magnetic fields in the aircraft. Deviation error, which is different on each heading, is compensated by the technician "swinging" the compass. A compass must be compensated so the deviation error on any heading is no greater than l0 degrees
Dewar bottle A vessel designed to hold liquefied gases. It has double walls with the space between being evacuated to prevent the transfer of heat. The surfaces in the vacuum area are made heat-reflective
Differential aileron travel Aileron movement in which the upward-moving aileron deflects a greater distance than the one moving downward. The up aileron produces parasite drag to counteract the induced drag caused by the down aileron. Differential aileron travel is used to counteract adverse yaw
Differential pressure The difference between two pressures. An airspeed indicator is a differential-pressure gauge. It measures the difference between static air pressure and pitot air pressure
Differential-voltage reverse-current cutout A type of reverse-current cutout switch used with heavy-duty electrical systems. This switch connects the generator to the electrical bus when the generator voltage is a specific amount higher than the battery voltage
Digital multimeter An electrical test instrument that can be used to measure voltage, current, and resistance. The indication is in the form of a liquid crystal display in discrete numbers
Dihedral The positive angle formed between the lateral axis of an airplane and a line that passes through the center of the wing or horizontal stabilizer. Dihedral increases the lateral stability of an airplane
Diluter-demand oxygen system A popular type of oxygen system in which the oxygen is metered to the mask, where it is diluted with cabin air by an airflow-metering aneroid assembly which regulates the amount of air allowed to dilute the oxygen on the basis of cabin altitude. The mixture of oxygen and air flows only when the wearer of the mask inhales. The percentage of oxygen in the air delivered to the mask is regulated, on the basis of altitude, by the regulator. A diluter-demand regulator has an emergency position which allows l00 percent oxygen to flow to the mask, by-passing the regulating mechanism
Dipole antenna A half wavelength, center-fed radio antenna. The length of each of the two arms is approximately one fourth of the wavelength of the center frequency for which the antenna is designed
Dirigible A large, cigar-shaped, rigid, lighter-than-air flying machine. Dirigibles are made of a rigid truss structure covered with fabric. Gas bags inside the structure contain the lifting gas, which is either helium or hydrogen
Disc area (helicopter specification) The total area swept by the blades of a helicopter main rotor.
Divergent oscillation Oscillation whose amplitude increases with time.
Diverging duct A duct, or passage, whose cross-sectional area increases in the direction of fluid flow.
DME See Distance measuring equipment.
Dope proofing The treatment of a structure to be covered with fabric to keep the solvents in the dope from softening the protective coating on the structure.
Dope roping A condition of aircraft dope brushed onto a surface in such a way that it forms a stringy, uneven surface rather than flowing out smoothly.
Double-acting actuator (hydraulic system component) A linear actuator moved in both directions by fluid power.
Double-acting hand pump (hydraulic system component) A hand-operated fluid pump that moves fluid during both strokes of the pump handle.
Doubler A piece of sheet metal used to strengthen and stiffen a repair in a sheet metal structure.
Downtime Any time during which an aircraft is out of commission and unable to be operated.
Downwash Air forced down by aerodynamic action below and behind the wing of an airplane or the rotor of a helicopter. Aerodynamic lift is produced when the air is deflected downward. The upward force on the aircraft is the same as the downward force on the air
Drag (helicopter rotor blade movement) Fore-and-aft movement of the tip of a helicopter rotor blade in its plane of rotation.
Dragging brakes Brakes that do not fully release when the brake pedal is released. The brakes are partially applied all the time, which causes excessive lining wear and heat
Drag wire A structural wire inside a Pratt truss airplane wing between the spars. Drag wires run from the front spar inboard, to the rear spar at the next bay outboard. Drag wires oppose the forces that try to drag the wing backward
Drill motor An electric or pneumatic motor that drives a chuck that holds a twist drill. The best drill motors produce high torque, and their speed can be controlled
Drip stick A fuel quantity indicator used to measure the fuel level in the tank when the aircraft is on the ground. The drip stick is pulled down from the bottom of the tank until fuel drips from its opened end. This indicates that the top of the gauge inside the tank is at the level of the fuel. Note the number of inches read on the outside of the gauge at the point it contacts the bottom of the tank, and use a drip stick table to convert this measurement into gallons of fuel in the tank
Dry air pump An engine-driven air pump which used carbon vanes. Dry pumps do not use any lubrication, and the vanes are extremely susceptible to damage from the solid airborne particles. These pumps must be operated with filters in their inlet so they will take in only filtered air
Dry ice Solidified carbon dioxide. Dry ice sublimates, or changes from a solid directly into a gas, at a temperature of -ll0 °F (-78.5 °C).
Dry rot Decomposition of wood fibers caused by fungi. Dry rot destroys all strength in the wood
Ductility The property of a material that allows it to be drawn into a thin section without breaking.
Dummy load (electrical load) A noninductive, high-power, 50-ohm resistor that can be connected to a transmission line in place of the antenna. The transmitter can be operated into the dummy load without transmitting any signal
Duralumin The name for the original alloy of aluminum, magnesium, manganese, and copper. Duralumin is the same as the modern 20l7 aluminum alloy
Dutch roll An undesirable, low-amplitude coupled oscillation about both the yaw and roll axes that affects many swept wing airplanes. Dutch roll is minimized by the use of a yaw damper
Dutchman shears A common name for compound-action sheet metal shears.
Dynamic pressure (q) The pressure a moving fluid would have if it were stopped. Dynamic pressure is measured in pounds per square foot
Dynamic stability The stability that causes an aircraft to return to a condition of straight and level flight after it has been disturbed from this condition. When an aircraft is disturbed from the straight and level flight, its static stability starts it back in the correct direction; but it overshoots, and the corrective forces are applied in the opposite direction. The aircraft oscillates back and forth on both sides of the correct condition, with each oscillation smaller than the one before it. Dynamic stability is the decreasing of these restorative oscillations
EADI Electronic Attitude Director Indicator.
ECAM Electronic Centralized Aircraft Monitor.
Eccentric brushing A special bushing used between the rear spar of certain cantilever airplane wings and the wing attachment fitting on the fuselage. The portion of the bushing that fits through the hole in the spar is slightly offset from that which passes through the holes in the fitting. By rotating the bushing, the rear spar may be moved up or down to adjust the root incidence of the wing
Eddy current damping Decreasing the amplitude of oscillations by the interaction of magnetic fields. In the case of a vertical-card magnetic compass, flux from the oscillating permanent magnet produces eddy currents in a damping disk or cup. The magnetic flux produced by the eddy currents opposes the flux from the permanent magnet and decreases the oscillations
Edge distance The distance between the center of a rivet hole and the edge of the sheet of metal.
EFIS Electronic Flight Instrument System.
EHSI Electronic Horizontal Situation Indicator.
EICAS Engine Indicating and Crew Alerting System.
Ejector A form of jet pump used to pick up a liquid and move it to another location. Ejectors are used to ensure that the compartment in which the boost pumps are mounted is kept full of fuel. Part of the fuel from the boost pump flowing through the ejector produces a low pressure that pulls fuel from the main tank and forces it into the boostpump sump area
Elastic limit The maximum amount of tensile load, in pounds per square inch, a material is able to withstand without being permanently deformed.
Electromotive force (EMF) The force that causes electrons to move from one atom to another within an electrical circuit. Electromotive force is an electrical pressure, and it is measured in volts
Electron current The actual flow of electrons in a circuit. Electrons flow from the negative terminal of a power source through the external circuit to its positive terminal. The arrowheads in semiconductor symbols point in the direction opposite to the flow of electron current
ELT (emergency locator transmitter) A self-contained radio transmitter that automatically begins transmitting on the emergency frequencies any time it is triggered by a severe impact parallel to the longitudinal axis of the aircraft.
Elevator downspring A spring in the elevator control system that produces a mechanical force that tries to lower the elevator. In normal flight, this spring force is overcome by the aerodynamic force from the elevator trim tab. But in slow flight with an aft CG position, the trim tab loses its effectiveness and the downspring lowers the nose to prevent a stall
Elevons Movable control surfaces on the trailing edge of a delta wing or a flying wing airplane. These surfaces operate together to serve as elevators, and differentially to act as ailerons
EMI Electromagnetic interference.
Enamel A type of finishing material that flows out to form a smooth surface. Enamel is usually made of a pigment suspended in some form of resin. When the resin cures, it leaves a smooth, glossy protective surface
Energizing brake A brake that uses the momentum of the aircraft to increase its effectiveness by wedging the shoe against the brake drum. Energizing brakes are also called servo brakes. A single-servo brake is energizing only when moving in the forward direction, and a duo-servo brake is energizing when the aircraft is moving either forward or backward
Epoxy A flexible, thermosetting resin that is made by polymerization of an epoxide. Epoxy has wide application as a matrix for composite materials and as an adhesive that bonds many different types of materials. It is noted for its durability and its chemical resistance
Equalizing resistor A large resistor in the ground circuit of a heavy-duty aircraft generator through which all of the generator output current flows. The voltage drop across this resistor is used to produce the current in the paralleling circuit that forces the generators to share the electrical load equally
Ethylene dibromide A chemical compound added to aviation gasoline to convert some of the deposits left by the tetraethyl lead into lead bromides. These bromides are volatile and will pass out of the engine with the exhaust gases
Ethylene glycol A form of alcohol used as a coolant for liquid-cooled engines and as an anti-icing agent.
Eutectic material An alloy or solution that has the lowest possible melting point.
Evacuation (air conditioning servicing procedure) A procedure in servicing vapor-cycle cooling systems. A vacuum pump removes all the air from the system. Evacuation removes all traces of water vapor that could condense out, freeze, and block the system
Evaporator (air conditioning component) The component in a vapor-cycle cooling system in which heat from the aircraft cabin is absorbed into the refrigerant. As the heat is absorbed, the refrigerant evaporates, or changes from a liquid into a vapor. The function of the evaporator is to lower the cabin air temperature
Expander-tube brake A brake that uses hydraulic fluid inside a synthetic rubber tube around the brake hub to force rectangular blocks of brake-lining material against the rotating brake drum. Friction between the brake drum and the lining material slows the aircraft
Expansion wave The change in pressure and velocity of a supersonic flow of air as it passes over a surface which drops away from the flow. As the surface drops away, the air tries to follow it. In changing its direction, the air speeds up to a higher supersonic velocity and its static pressure decreases. There is no change in the total energy as the air passes through an expansion wave, and so there is no sound as there is when air passes through a shock wave
Extruded angle A structural angle formed by passing metal heated to its plastic state through specially shaped dies.
Fading of brakes The decrease in the amount of braking action that occurs with some types of brakes that are applied for a long period of time. True fading occurs with overheated drum-type brakes. As the drum is heated, it expands in a bell-mouthed fashion. This decreases the amount of drum in contact with the brake shoes and decreases the braking action. A condition similar to brake fading occurs when there is an internal leak in the brake master cylinder. The brakes are applied, but as the pedal is held down, fluid leaks past the piston, and the brakes slowly release
Fairing A part of a structure whose primary purpose is to produce a smooth surface or a smooth junction where two surfaces join.
Fairlead A plastic or wooden guide used to prevent a steel control cable rubbing against an aircraft structure.
FCC Federal Communications Commission.
FCC Flight Control Computer.
Feather (helicopter rotor blade movement) Rotation of a helicopter rotor blade about its pitch-change axis.
Ferrous metal Any metal that contains iron and has magnetic characteristics.
Fiber stop nut A form of a self-locking nut that has a fiber insert crimped into a recess above the threads. The hole in the insert is slightly smaller than the minor diameter of the threads. When the nut is screwed down over the bolt threads, the opposition caused by the fiber insert produces a force that prevents vibration loosening the nut
File A hand-held cutting tool used to remove a small amount of metal with each stroke.
Fill threads Threads in a piece of fabric that run across the width of the fabric, interweaving with the warp threads. Fill threads are often called woof, or weft, threads
Fillet A fairing used to give shape but not strength to an object. A fillet produces a smooth junction where two surfaces meet
Finishing tape Another name for surface tape. See surface tape
Fishmouth splice A type of splice used in a welded tubular structure in which the end of the tube whose inside diameter is the same as the outside diameter of the tube being spliced is cut in the shape of a V, or a fishmouth, and is slipped over the smaller tube welded. A fishmouth splice has more weld area than a butt splice and allows the stresses from one tube to transfer into the other tube gradually
Fire pull handle The handle in an aircraft flight deck that is pulled at the first indication of an engine fire. Pulling this handle removes the generator from the electrical system, shuts off the fuel and hydraulic fluid to the engine, and closes the compressor bleed air valve. The fire extinguisher agent discharge switch is uncovered, but it is not automatically closed
Fire zone A portion of an aircraft designated by the manufacturer to require fire-detection and/or fire-extinguishing equipment and a high degree of inherent fire resistance.
Fitting An attachment device that is used to connect components to an aircraft structure.
Fixed fire-extinguishing system A fire-extinguishing system installed in an aircraft.
Flameout A condition in the operation of a gas turbine engine in which the fire in the engine unintentionally goes out.
Flap (aircraft control) A secondary control on an airplane wing that changes its camber to increase both its lift and its drag.
Flap (helicopter rotor blade movement) Up-and-down movement of the tip of a helicopter rotor blade.
Flap overload valve A valve in the flap system of an airplane that prevents the flaps being lowered at an airspeed which could cause structural damage. If the pilot tries to extend the flaps when the airspeed is too high, the opposition caused by the air flow will open the overload valve and return the fluid to the reservoir
Flash point The temperature to which a material must be raised for it to ignite, but not continue to burn, when a flame is passed above it.
Flat pattern layout The pattern for a sheet metal part that has the material used for each flat surface, and for all of the bends, marked out with bend-tangent lines drawn between the flats and bend allowances.
Flight controller The component in an autopilot system that allows the pilot to maneuver the aircraft manually when the autopilot is engaged.
Fluid A form of material whose molecules are able to flow past one another without destroying the material. Gases and liquids are both fluids
Fluid power The transmission of force by the movement of a fluid. The most familiar examples of fluid power systems are hydraulic and pneumatic systems
Flutter Rapid and uncontrolled oscillation of a flight control surface on an aircraft that is caused by a dynamically unbalanced condition.
Fly-by-wire A method of control used by some modern aircraft in which control movement or pressures exerted by the pilot are directed into a digital computer where they are input into a program tailored to the flight characteristics of the aircraft. The computer output signal is sent to actuators at the control surfaces to move them the optimum amount for the desired maneuver
Flying boat An airplane whose fuselage is built in the form of a boat hull to allow it to land and takeoff from water. In the past, flying boats were a popular form of large airplane
Flying wing A type of heavier-than-air aircraft that has no fuselage or separate tail surfaces. The engines and useful load are carried inside the wing, and movable control surfaces on the trailing edge provide both pitch and roll control
Foot-pound A measure of work accomplished when a force of l pound moves an object a distance of l foot.
Forehand welding Welding in which the torch is pointed in the direction the weld is progressing.
Form drag Parasite drag caused by the form of the object passing through the air.
Former An aircraft structural member used to give a fuselage its shape.
FMC Flight Management Computer.
Forward bias A condition of operation of a semiconductor device such as a diode or transistor in which a positive voltage is connected to the P-type material and a negative voltage to the N-type material.
FPD Freezing point depressant.
Fractional distillation A method of separating the various components from a physical mixture of liquids. The material to be separated is put into a container and its temperature is increased. The components having the lowest boiling points boil off first and are condensed. Then, as the temperature is further raised, other components are removed. Kerosene, gasoline, and other petroleum products are obtained by fractional distillation of crude oil
Frangible Breakable, or easily broken.
Freon The registered trade name for a refrigerant used in a vapor-cycle air conditioning system.
Frise aileron An aileron with its hinge line set back from the leading edge so that when it is deflected upward, part of the leading edge projects below the wing and produces parasite drag to help overcome adverse yaw.
Full-bodied Not thinned.
Fully articulated rotor A helicopter rotor whose blades are attached to the hub in such a way that they are free to flap, drag, and feather. See each of these terms
Frost Ice crystal deposits formed by sublimation when the temperature and dew point are below freezing.
Fuel-flow transmitter A device in the fuel line between the engine-driven fuel pump and the carburetor that measures the rate of flow of the fuel. It converts this flow rate into an electrical signal and sends it to an indicator in the instrument panel
Fuel jettison system A system installed in most large aircraft that allows the flight crew to jettison, or dump, fuel to lower the gross weight of the aircraft to its allowable landing weight. Boost pumps in the fuel tanks move the fuel from the tank into a fuel manifold. From the fuel manifold, it flows away from the aircraft through dump chutes is each wing tip. The fuel jettison system must be so designed and constructed that it is free from fire hazards
Fuel totalizer A fuel quantity indicator that gives the total amount of fuel remaining on board the aircraft on one instrument. The totalizer adds the quantities of fuel in all of the tanks
Fungus (plural: fungi) Any of several types of plant life that include yeasts, molds, and mildew.
Fusible plugs Plugs in the wheels of high-performance airplanes that use tubeless tires. The centers of the plugs are filled with a metal that melts at a relatively low temperature. If a takeoff is aborted and the pilot uses the brakes excessively, the heat transferred into the wheel will melt the center of the fusible plugs and allow the air to escape from the tire before it builds up enough pressure to cause an explosion
Gauge (rivet) The distance between rows of rivets in a multirow seam. Gauge is also called transverse pitch
Gauge pressure Pressure referenced from the existing atmospheric pressure.
Galling Fretting or pulling out chunks of a surface by sliding contact with another surface or body.
Gasket A seal between two parts where there is no relative motion.
Gear-type pump A constant-displacement fluid pump that contains two meshing large-tooth spur gears. Fluid is drawn into the pump as the teeth separate and is carried around the inside of the housing with teeth and is forced from the pump when the teeth come together
General Aviation Airworthiness Alerts Documents published by the FAA that provide an economical interchange of service experience and cooperation in the improvement of aeronautical product durability, reliability, and safety. Alerts include items that have been reported to be significant, but which have not been fully evaluated at the time the material went to press
Generator A mechanical device that transforms mechanical energy into electrical energy by rotating a coil inside a magnetic field. As the conductors in the coil cut across the lines of magnetic flux, a voltage is generated that causes current to flow
Generator series field A set of heavy field windings in a generator connected in a series with the armature. The magnetic field produced by the series windings is used to change the characteristics of the generator
Generator shunt field A set of field windings in a generator connected in parallel with the armature. Varying the amount of current flowing in the shunt field windings controls the voltage output of the generator
Gerotor pump A form of constant-displacement gear pump. A gerotor pump uses an external-tooth spur gear that rides inside of and drives an internal-tooth rotor gear. There is one more tooth space inside the rotor than there are teeth on the drive gear. As the gears rotate, the volume of the space between two of the teeth on the inlet side of the pump increases, while the volume of the space between the two teeth on the opposite side of the pump decreases
GHz (gigahertz) 1,000,000,000 cycles per second.
Gimbal A support that allows a gyroscope to remain in an upright condition when its base is tilted.
Glass cockpit An aircraft instrument system that uses a few cathode-ray-tube displays to replace a large number of mechanically actuated instruments.
Glaze ice Ice that forms when large drops of water strike a surface whose temperature is below freezing. Glaze ice is clear and heavy
Glide slope The portion of an ILS (Instrument Landing System) that provides the vertical path along which an aircraft descends on an instrument landing.
Gram The basic unit of weight or mass in the metric system. One gram equals approximately 0.035 ounce
Graphite A form of carbon. Structural graphite is used in composite structure because of its strength and stiffness
Greige (pronounced "gray") The unshrunk condition of a polyester fabric as it is removed from the loom.
Ground The voltage reference point in an aircraft electrical system. Ground has zero electrical potential. Voltage values, both positive and negative, are measured from ground. In the United Kingdom, ground is spoken of as "earth."
Ground-power unit (GPU) A service component used to supply electrical power to an aircraft when it is being operated on the ground.
Guncotton A highly explosive material made by treating cotton fibers with nitric and sulfuric acids. Guncotton is used in making the film base of nitrate dope
Gusset A small plate attached to two or more members of a truss structure. A gusset strengthens the truss
Gyro (gyroscope) The sensing device in an autopilot system. A gyroscope is a rapidly spinning wheel with its weight concentrated around its rim. Gyroscopes have two basic characteristics that make them useful in aircraft instruments: rigidity in space and precession. See rigidity in space and precession
Gyroscopic precession The characteristic of a gyroscope that causes it to react to an applied force as though the force were applied at a point 90° in the direction of rotation from the actual point of application. The rotor of a helicopter acts in much the same way as a gyroscope and is affected by gyroscopic precession
Halon 1211 A halogenated hydrocarbon fire-extinguishing agent used in many HRD fire-extinguishing systems for powerplant protection. The technical name for Halon 1211 is bromochlorodifluoromethane
Halon 1301 A halogenated hydrocarbon fire-extinguishing agent that is one of the best for extinguishing cabin and powerplant fires. It is highly effective and is the least toxic of the extinguishing agents available. The technical name for Halon 1301 is bromotrifluoromethane
Hangar rash Scrapes, bends, and dents in an aircraft structure caused by careless handling.
Hardwood Wood from a broadleaf tree that sheds its leaves each year.
Heat exchanger A device used to exchange heat from one medium to another. Radiators, condensers, and evaporators are all examples of heat exchangers. Heat always moves from the object or medium having the greatest level of heat energy to a medium or object having a lower level
Helix A screw-like, or spiral, curve.
Hertz One cycle per second.
Holding relay An electrical relay that is closed by sending a pulse of current through the coil. It remains closed until the current flowing through its contacts is interrupted
Homebuilt aircraft Aircraft that are built by individuals as a hobby rather than by factories as commercial products. Homebuilt, or amateur-built, aircraft are not required to meet the stringent requirements imposed on the manufacture of FAA-certified aircraft
Hot dimpling A process used to dimple, or indent, the hole into which a flush rivet is to be installed. Hot dimpling is done by clamping the metal between heating elements and forcing the dies through the holes in the softened metal. Hot dimpling prevents hard metal from cracking when it is dimpled
Hot-wire cutter A cutter used to shape blocks of Styrofoam. The wire is stretched tight between the arms of a frame and heated by electrical current. The hot wire melts its way through the foam
HRD High-rate-discharge.
HSI See Horizontal situation indicator.
Hydraulic actuator The component in a hydraulic system that converts hydraulic pressure into mechanical force. The two main types of hydraulic actuators are linear actuators (cylinders and pistons) and rotary actuators (hydraulic motors)
Hydraulic fuse A type of flow control valve that allows a normal flow of fluid in the system but, if the flow rate is excessive, or if too much fluid flows for normal operation, the fuse will shut off all further flow.
Hydraulic motor A hydraulic actuator that converts fluid pressure into rotary motion. Hydraulic motors have an advantage in aircraft installations over electric motors, because they can operate in a stalled condition without the danger of a fire
Hydraulic power pack A small, self-contained hydraulic system that consists of a reservoir, pump, selector valves, and relief valves. The power pack is removable from the aircraft as a unit to facilitate maintenance and service
Hydraulics The system of fluid power which transmits force through an incompressible fluid.
Hydrocarbon An organic compound that contains only carbon and hydrogen. The vast majority of fossil fuels, such as gasoline and turbine-engine fuel, are hydrocarbons
Hydrostatic test A pressure test used to determine the serviceability of high-pressure oxygen cylinders. The cylinders are filled with water and pressurized to 5/3 of their working pressure. Standard-weight cylinders (DOT 3AA) must by hydrostatically tested every five years, and lightweight cylinders (DOT 3HT) must be tested every three years
Hypersonic speed Speed of greater than Mach 5 (5 times the speed of sound).
Hyperbolic navigation Electronic navigation systems that determine aircraft location by the time difference between reception of two signals. Signals from two stations at different locations will be received in the aircraft at different times. A line plotted between two stations along which the time difference is the same forms a hyperbola
Hypoxia A physiological condition in which a person is deprived of the needed oxygen. The effects of hypoxia normally disappear as soon as the person is able to breathe air containing sufficient oxygen
Icebox rivet A solid rivet made of 20l7 or 2024 aluminum alloy. These rivets are too hard to drive in the condition they are received from the factory, and must be heat-treated to soften them. They are heated in a furnace and then quenched in cold water. Immediately after quenching they are soft, but within a few hours at room temperature they become quite hard. The hardening can be delayed for several days by storing them in a subfreezing icebox and holding them at this low temperature until they are to be used
Inch-pound A measure of work accomplished when a force of l pound moves an object a distance of l inch.
Induced current Electrical current produced in a conductor when it is moved through or crossed by a magnetic field.
Induced drag Aerodynamic drag produced by an airfoil when it is producing lift. Induced drag is affected by the same factors that affect induced lift
Induction time The time allowed an epoxy or polyurethane material between its initial mixing and its application. This time allows the materials to begin their cure
Infrared radiation Electromagnetic radiation whose wavelengths are longer than those of visible light.
Ingot A large block of metal that was molded as it was poured from the furnace. Ingots are further processed into sheets, bars, tubes, or structural beams
INS See Inertial Navigation System.
Inspection Authorization (IA) An authorization that may be issued to an experienced aviation maintenance technician who holds both an Airframe and Powerplant rating. It allows the holder to conduct annual inspections and to approve an aircraft or aircraft engine for return to service after a major repair or major alteration
Integral fuel tank A fuel tank which is formed by sealing off part of the aircraft structure and using it as a fuel tank. An integral wing tank is called a "wet wing." Integral tanks are used because of their large weight saving. The only way of repairing an integral fuel tank is by replacing damaged sealant and making riveted repairs, as is done with any other part of the aircraft structure
Interference drag Parasite drag caused by air flowing over one portion of the airframe interfering with the smooth flow of air over another portion.
Intermittent-duty solenoid A solenoid-type switch whose coil is designed for current to flow through it for only a short period of time. The coil will overheat if current flows through it too long
IRS Inertial Reference System.
IRU Inertial Reference Unit.
Iso-octane A hydrocarbon, C8Hl8, which has very high critical pressure and temperature. Iso-octane is used as the high reference for measuring the antidetonation characteristics of a fuel
Isobaric mode The mode of pressurization in which the cabin pressure is maintained at a constant value regardless of the outside air pressure.
Isogonic line A line drawn on an aeronautical chart along which the angular difference between the magnetic and geographic north poles is the same.
Isopropyl alcohol A colorless liquid used in the manufacture of acetone and its derivatives and as a solvent and anti-icing agent.
Jackscrew A hardened steel rod with strong threads cut into it. A jackscrew is rotated by hand or with a motor to apply a force or to lift an object
Jet pump A special venturi in a line carrying air from certain areas in an aircraft that need an augmented flow of air through them. High-velocity compressor bleed air is blown into the throat of a venturi where it produces a low pressure that pulls air from the area to which it is connected. Jet pumps are often used in the lines that pull air through galleys and toilet areas
Joggle A small offset near the edge of a piece of sheet metal. It allows one sheet of metal to overlap another sheet while maintaining a flush surface
Jointer A woodworking power tool used to smooth edges of a piece of wood.
K-factor A factor used in sheet metal work to determine the setback for other than a 90° bend. Setback = K • (bend radius + metal thickness). For bends of less than 90°, the value of K is less than 1; for bends greater than 90°, the value of K is greater than 1
Kevlar A patented synthetic aramid fiber noted for its flexibility and light weight. It is to a great extent replacing fiberglass as a reinforcing fabric for composite construction
Key (verb) To initiate an action by depressing a key or a button.
kHz (kilohertz) 1,000 cycles per second.
Kick-in pressure The pressure at which an unloading valve causes a hydraulic pump to direct its fluid into the system manifold.
Kick-out pressure The pressure at which an unloading valve shuts off the flow of fluid into the system pressure manifold and directs it back to the reservoir under a much reduced pressure.
Kilogram One thousand grams.
Kinetic energy Energy that exists because of motion.
Knot (wood defect) A hard, usually round section of a tree branch embedded in a board. The grain of the knot is perpendicular to the grain of the board. Knots decrease the strength of the board and should be avoided where strength is needed
Knot (measure of speed) A speed measurement that is equal to one nautical mile per hour. One knot is equal to l.l5 statute mile per hour
Koroseal lacing A plastic lacing material available in round or rectangular cross sections and used for holding wire bundles and tubing together. It holds tension on knots indefinitely and is impervious to petroleum products
Kraft paper A tough brown wrapping paper, like that used for paper bags.
Labyrinth seal A type of seal in a Roots blower cabin supercharger that is made in the form of knife edges riding in step-shaped grooves. Air pressure is dropped in each section of the seal, and any oil in the air is trapped in the grooves
Lacquer A finishing material made of a film base, solvents, plasticizers, and thinners. The film base forms a tough film over the surface when it dries. The solvents dissolve the film base so it can be applied as a liquid. The plasticizers give the film base the needed resilience, and the thinners dilute the lacquer so it can be applied with a spray gun. Lacquer is sprayed on the surface as a liquid, and when the solvents and thinners evaporate, the film base remains as a tough decorative and protective coating
Landing gear warning system A system of lights used to indicate the condition of the landing gear. A red light illuminates when any of the gears are in an unsafe condition; a green light shows when all of the gears are down and locked, and no light is lit when the gears are all up and locked. An aural warning system is installed that sounds a horn if any of the landing gears are not down and locked when the throttles are retarded for landing
Laminar flow Airflow in which the air passes over the surface in smooth layers with a minimum of turbulence.
Laminated wood A type of wood made by gluing several pieces of thin wood together. The grain of all pieces runs in the same direction
Latent heat Heat that is added to a material that causes a change in its state without changing its temperature.
Lay-up The placement of the various layers of resin- impregnated fabric in the mold for a piece of laminated composite material.
LID ratio A measure of efficiency of an airfoil. It is the ratio of the lift to the total drag at a specified angle of attack
Left-right indicator The course-deviation indicator used with a VOR navigation system.
Lightening hole A hole cut in a piece of structural material to get rid of weight without losing any strength. A hole several inches in diameter may be cut in a piece of metal at a point where the metal is not needed for strength, and the edges of the hole are flanged to give it rigidity. A piece of metal with properly flanged lightening holes is more rigid than the metal before the holes were cut
Linear actuator A fluid power actuator that uses a piston moving inside a cylinder to change pressure into linear, or straight-line, motion.
Linear change A change in which the output is directly proportional to the input.
Load meter A current meter used in some aircraft electrical systems to show the amount of current the generator or alternator is producing. Loadmeters are calibrated in percent of the generator rated output
Lodestone A magnetized piece of natural iron oxide.
Logic flow chart A type of graphic chart that can be made up for a specific process or procedure to help follow the process through all of its logical steps.
LORAN A Long Range Aid to Navigation. A hyperbolic navigation system that operates with frequencies of l,950 kHz, l,850 kHz, and l,900 kHz
LORAN C The LORAN system used in aircraft. It operates on a frequency of l00 kHz
LRU Line replaceable unit.
Lubber line A reference on a magnetic compass and directional gyro that represents the nose of the aircraft. The heading of the aircraft is shown on the compass card opposite the lubber line
Mach number A measurement of speed based on the ratio of the speed of the aircraft to the speed of sound under the same atmospheric conditions. An airplane flying at Mach l is flying at the speed of sound
Major alteration An alteration not listed in the aircraft, aircraft engine, or propeller specifications. It is one that might appreciably affect weight, balance, structural strength performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness, or that cannot be made with elementary operations
Major repair A repair to an aircraft structure or component that if improperly made might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness, or that is not done according to accepted practices, or cannot be made with elementary operation.
Manifold cross-feed fuel system A type of fuel system commonly used in large transport category aircraft. All fuel tanks feed into a common manifold, and the dump chutes and the single-point fueling valves are connected to the manifold. Fuel lines to each engine are taken from the manifold
Manifold pressure The absolute pressure of the air in the induction system of a reciprocating engine.
Manifold pressure gauge A pressure gauge that measures the absolute pressure inside the induction system of a reciprocating engine. When the engine is not operating, this instrument shows the existing atmospheric pressure
Master switch A switch in an aircraft electrical system that can disconnect the battery from the bus and open the generator or alternator field circuit.
Matrix The material used in composite construction to bond the fibers together and to transmit the forces into the fibers. Resins are the most widely used matrix materials
Mean camber A line that is drawn midway between the upper and lower camber of an airfoil section. The mean camber determines the aerodynamic characteristics of the airfoil
MEK Methyl-ethyl-ketone is an organic chemical solvent that is soluble in water and is used as a solvent for vinyl and nitrocellulose films. MEK is an efficient cleaner for preparing surfaces for priming or painting
Mercerize A treatment given to cotton thread to make it strong and lustrous. The thread is stretched while it is soaked in a solution of caustic soda
MHz (megahertz) 1,000,000 cycles per second.
Microballoons Tiny, hollow spheres of glass or phenolic material used to add body to a resin.
Microbial contaminants The scum that forms inside the fuel tanks of turbine-engine-powered aircraft that is caused by micro-organisms. These micro-organisms live in water that condenses from fuel, and they feed on the fuel. The scum they form clogs fuel filters, lines, and fuel controls and holds water in contact with the aluminum alloy structure, causing corrosion
Micro-Mesh A patented graduated series of cloth-backed cushioned seats that contain abrasive crystals. Micro-Mesh is used for polishing and restoring transparency to acrylic plastic windows and windshields
Micron ("micro meter") A unit of linear measurement equal to one millionth of a meter, one thousandth of a millimeter, or 0.000039 inch. A micron is also called a micrometer
Micronic filter The registered trade name of a type of fluid filter whose filtering element is a specially treated cellulose paper formed into vertical convolutions, or wrinkles. Micronic filters prevent the passage of solids larger than about l0 microns, and are normally replaced with new filters rather than cleaned
Micro-organism An organism, normally bacteria or fungus, or microscopic size.
Microswitch The registered trade name for a precision switch that uses a short throw of the control plunger to actuate the contacts. Microswitches are used primarily as limit switches to control electrical units automatically
MIG welding Metal inert gas welding is a form of electric arc welding in which the electrode is an expendable wire. MIG welding is now called GMA (gas metal arc) welding
Mil One thousandth of an inch (0.001 inch). Paint film thickness is usually measured in mils
Mildew A gray or white fungus growth that forms on organic materials. Mildew forms on cotton and linen aircraft fabric and destroys its strength
Millivoltmeter An electrical instrument that measures voltage in units of millivolts (thousandths of a volt).
Mist coat A very light coat of zinc chromate primer. It is so thin that the metal is still visible, but the primer makes pencil marks easy to see
Moisture separator A component in a high-pressure pneumatic system that removes most of the water vapor from the compressed air. When the compressed air is used, its pressure drops, and this pressure drop causes a drop in temperature. If any moisture were allowed to remain in the air, it would freeze and block the system
Mold line A line used in the development of a flat pattern for a formed piece of sheet metal. The mold line is an extension of the flat side of a part beyond the radius. The mold line dimension of a part is the dimension made to the intersection of mold lines and is the dimension the part would have if its corners had no radius
Mold point The intersection of two mold lines of a part. Mold line dimensions are made between mold points
Moment A force that causes or tries to cause an object to rotate. The value of a moment is the product of the weight of an object (or the force), multiplied by the distance between the center of gravity of the object (and the point of application of the force) and the fulcrum about which the object rotates
Monel An alloy of nickel, copper, and aluminum or silicon.
MSDS Material Safety Data Sheets. MSDS are required by the Federal Government to be available in workplaces to inform workers of the dangers that may exist from contact with certain materials
MTBF Mean time between failures.
Multimeter An electrical test instrument that consists of a single current-measuring meter and all of the needed components to allow the meter to be used to measure voltage, resistance, and current. Multimeters are available with either analog-or digital-type displays
Multiple-disk brakes Aircraft brakes in which one set of disks is keyed to the axle and remains stationary. Between each stationary disk there is a rotating disk that is keyed to the inside of the wheel. When the brakes are applied, the stationary disks are forced together, clamping the rotating disks between them. The friction between the disks slows the aircraft
Nailing strip A method of applying pressure to the glue in a scarf joint repair in a plywood skin. A strip of thin plywood is nailed over the glued scarf joint with the nails extending into a supporting structure beneath the skin. The strip is installed over vinyl sheeting to prevent it sticking to the skin. When the glue is thoroughly dry, the nailing strip is broken away and the nails removed
Nap of the fabric The ends of the fibers in a fabric. The first coat of dope on cotton or linen fabric raises the nap, and the fiber ends stick up. These ends must be carefully removed by sanding to get a smooth finish
Naphtha A volatile and flammable hydrocarbon liquid used chiefly as a solvent or as a cleaning fluid.
Negative pressure relief valve (pressurization component) A valve that opens anytime the outside air pressure is greater than the cabin pressure. It prevents the cabin altitude from ever becoming greater than the aircraft flight altitude
Neutral axis (neutral plane) A line through a piece of material that is bent. The material in the outside of the bend is stretched and that on the inside of the bend is shrunk. The material along the neutral plane is neither shrunk nor stretched
Neutral flame An oxyacetylene flame produced when the ratio of oxygen and acetylene is chemically correct and there is no excess of oxygen or carbon. A neutral flame has a rounded inner cone and no feather around it
Noise (electrical) An unwanted electrical signal within a piece of electronic equipment.
Nomex A patented nylon material used to make the honeycomb core for certain types of sandwich materials.
Nonenergizing brake A brake that does not use the momentum of the aircraft to increase the friction.
Nonvolatile memory Memory in a computer that is not lost when power to the computer is lost.
Normal heptane A hydrocarbon, C7Hl6, with a very low critical pressure and temperature. Normal heptane is used as the low reference in measuring the anti-detonation characteristics of a fuel
Normal shock wave A shock wave that forms ahead of a blunt object moving through the air at the speed of sound. The shock wave is normal (perpendicular) to the air approaching the object. Air passing through a normal shock wave is slowed to a subsonic speed and its static pressure is increased
Normalizing A process of strain-relieving steel that has been welded and left in a strained condition. The steel is heated to a specified temperature, usually red hot, and allowed to cool in still air to room temperature
Nose-gear centering cam A cam in the nose-gear shock strut that causes the piston to center when the strut fully extends. When the aircraft takes off and the strut extends, the wheel is straightened in its fore-and-aft position so it can be retracted into the wheel well
NPN transistor A bipolar transistor made of a thin base of P-type silicon or geranium sandwiched between a collector and an emitter, both of which are made of N-type material.
Null position The position of an ADF loop antenna when the signal being received is canceled in the two sides of the loop and the signal strength is the weakest.
Oblique shock wave A shock wave that forms on a sharp- pointed object moving through air at a speed greater than the speed of sound. Air passing through an oblique shock wave is slowed down, but not to a subsonic speed, and its static pressure is increased
Oleo shock absorber A shock absorber used on aircraft landing gear. The initial landing impact is absorbed by oil transferring from one compartment in the shock strut into another compartment through a metering orifice. The shocks of taxiing are taken up by a cushion of compressed air
Octane rating A rating of the anti-detonation characteristics of a reciprocating engine fuel. It is based on the performance of the fuel in a special test engine. When a fuel is given a dual rating such as 80/87, the first number is its anti-detonating rating with a lean fuel-air mixture, and the higher number is its rating with a rich mixture
Open angle An angle in which sheet metal is bent less than 90°.
Open assembly time The period of time between the application of the glue and the assembly of the joint components.
Open-hydraulic system A fluid power system in which the selector valves are arranged in series with each other. Fluid flows from the pump through the center of the selector valves, back into the reservoir when no unit is being actuated
Open-center selector valve A type of selector valve that functions as an unloading valve as well as a selector valve. Open-center selector valves are installed in series, and when no unit is actuated, fluid from the pump flows through the centers of all the valves and returns to the reservoir. When a unit is selected for actuation, the center of the selector valve is shut off and the fluid from the pump goes through the selector valve into one side of the actuator. Fluid from the other side of the actuator returns to the valve and goes back to the reservoir through the other selector valves. When the actuation is completed, the selector valve is placed in its neutral position. Its center opens, and fluid from the pump flows straight through the valve
Open wiring An electrical wiring installation in which the wires are tied together in bundles and clamped to the aircraft structure rather than being enclosed in conduit.
Orifice check valve A component in a hydraulic or pneumatic system that allows unrestricted flow in one direction, and restricted flow in the opposite direction.
O-ring A widely used type of seal made in the form of a rubber ring with a round cross section. An O-ring seals in both directions, and it can be used as a packing or a gasket
Ornithopter A heavier-than-air flying machine that produces lift by flapping its wings. No practical ornithopter has been built
Oscilloscope An electrical instrument that displays on the face of a cathode-ray tube the waveform of the electrical signal it is measuring.
Outflow valve (pressurization component) A valve in the cabin of a pressurized aircraft that controls the cabin pressure by opening to relieve all pressure above that for which the cabin pressure control is set.
Overvoltage protector A component in an aircraft electrical system that opens the alternator field circuit any time the alternator output voltage is too high.
Oxidizing flame An oxyacetylene flame in which there is an excess of oxygen. The inner cone is pointed and often a hissing sound is heard
Ozone An unstable form of oxygen produced when an electric spark passes through the air. Ozone is harmful to rubber products
Packing A seal between two parts where there is relative motion.
Paint A covering applied to an object or structure to protect it and improve its appearance. Paint consists of a pigment suspended in a vehicle such as oil or water. When the vehicle dries by evaporation or curing, the pigment is left as a film on the surface
Parabolic reflector A reflector whose surface is made in the form of a parabola.
Parallel circuit A method of connecting electrical components so that each component is in a path between the terminals of the source of electrical energy.
Paralleling circuit A circuit in a multi-engine aircraft electrical system that controls a flow of control current which is used to keep the generators or alternators sharing the electrical load equally. The relay opens automatically to shut off the flow of paralleling current any time the output of either alternator or generator drops to zero
Paralleling relay A relay in multi-engine aircraft electrical system that controls a flow of control current which is used to keep the generators or alternators sharing the electrical load equally. The relay opens automatically to shut off the flow of paralleling current any time the output of either alternator or generator drops to zero
Parent metal The metal being welded. This term is used to distinguish between the metal being welded and the welding rod
Partial pressure The percentage of the total pressure of a mixture of gases produced by each of the individual gases in the mixture.
Parting film A layer of thin plastic material placed between a composite lay-up and the heating blanket. It prevents the blanket from sticking to the fabric
Pascal's Law A basic law of fluid power which states that the pressure in an enclosed container is transmitted equally and undiminished to all points of the container, and the force acts at right angles to the enclosing walls.
Performance number The anti-detonation rating of a fuel that has a higher critical pressure and temperature than iso- octane (a rating of l00). Iso-octane that has been treated with varying amounts of tetraethyl lead is used as the reference fuel
Petrolatum-zinc dust compound A special abrasive compound used inside an aluminum wire terminal being swaged onto a piece of aluminum electrical wire. When the terminal is compressed, the zinc dust abrades the oxides from the wire, and the petrolatum prevents oxygen reaching the wire so no more oxides can form
Petroleum fractions The various components of a hydrocarbon fuel that are separated by boiling them off at different temperatures in the process of fractional distillation.
Phased array antenna A complex antenna which consists of a number of elements. A beam of energy is formed by the superimposition of the signals radiating from the elements. The direction of the beam can be changed by varying the relative phase of the signals applied to each of the elements
Phenolic plastic A plastic material made of a thermosetting phenol-formaldehyde resin, reinforced with cloth or paper. Phenolic plastic materials are used for electrical insulators and for chemical-resistant table tops
Pilot hole A small hole punched or drilled in a piece of sheet metal to locate a rivet hole.
Pin knot cluster A group of knots, all having a diameter of less than approximately 1/l6 inch.
Pinked-edge tape Cloth tape whose edges have small V-shaped notches cut along their length. The pinked edges prevent the tape from raveling
Pinking shears Shears used to cut aircraft fabric with a series of small notches along the cut edge.
Pinion A small gear that meshes with a larger gear, a sector of a gear, or a toothed rack.
Piston A sliding plug in an actuating cylinder used to convert pressure into force and then into work.
Pitch (aircraft maneuver) Rotation of an aircraft about its lateral axis.
Pitch (rivet) The distance between the centers of adjacent rivets installed in the small row.
Pitch pocket (wood defect) Pockets of pitch that appear in the growth rings of a piece of wood.
Pitot pressure Ram air pressure used to measure airspeed. The pitot tube faces directly into the air flowing around the aircraft. It stops the air and measures its pressure
Plain-weave fabric Fabric in which each warp thread passes over one fill thread and under the next. Plain-weave fabric typically has the same strength in both warp and fill directions
Plan position indicator (PPI) A type of radar scope that shows both the direction and distance of the target from the radar antenna. Some radar antenna rotate and their PPI scopes are circular. Other antenna oscillate and their PPI scopes are fan shaped
Planer A woodworking power tool used to smooth the surfaces of a piece of wood.
Plasticizer A constituent in dope or lacquer that gives its film flexibility and resilience.
Plastic media blasting (PMB) A method of removing paint from an aircraft surface by dry-blasting it with tiny plastic beads.
Plastics The generic name for any of the organic materials produced by polymerization. Plastics can be shaped by molding or drawing
Plenum An enclosed chamber in which air can be held at a pressure higher than that of the surrounding air.
Ply rating The rating of an aircraft tire that indicates its relative strength. The ply rating does not indicate the actual number of plies of fabric in the tire; it indicates the number of piles of cotton fabric needed to produce the same strength as the actual piles
Plywood A wood product made by gluing several pieces of thin wood veneer together. The grain of the wood in each layer runs at 90° or 45° to the grain of the layer next to it
Pneumatics The system of fluid power which transmits force by the use of a compressible fluid.
PNP transistor A bipolar transistor made of a thin base of N-type silicon or germanium sandwiched between a collector and an emitter, both of which are made of P-type material.
Polyester fibers A synthetic fiber made by the polymerization process in which tiny molecules are united to form a long chain of molecules. Polyester fibers are woven into fabrics that are known by their trade names of Dacron, Fortrel, and Kodel. Polyester film and sheet are known as Mylar and Celenar
Polyester resin A thermosetting resin used as a matrix for much of the fiberglass used in composite construction.
Polyurethane enamel A hard, chemically resistant finish used on aircraft. Polyurethane enamel is resistant to damage from all types of hydraulic fluid
Polyvinyl chloride A thermoplastic resin used in the manufacture of transparent tubing for electrical insulation and fluid lines which are subject to low pressures.
Potential energy Energy possessed in an object because of its position, chemical composition, shape, or configuration.
Potentiometer A variable resistor having connections to both ends of the resistance element and to the wiper that moves across the resistance.
Pot life The length of time a resin will remain workable after the catalyst has been added. If a catalyzed material is not used within its usable pot life, it must be discarded and a new batch mixed up
Power The time rate of doing work. Power is force multiplied by distance (work), divided by time
Power brakes Aircraft brakes that use the main hydraulic system to supply fluid for the brake actuation. Aircraft that require a large amount of fluid for their brake actuation normally use power brakes, and the volume of fluid sent to the brakes is increased by the use of deboosters
Power control valve A hand-operated hydraulic pump unloading valve. When the valve is open, fluid flows from the pump to the reservoir with little opposition. To actuate a unit, turn the selector valve, and manually close the power control valve. Pressurized fluid flows to the unit, and when it is completely actuated, the power control valve automatically opens
Preflight inspection A required inspection to determine the condition of the aircraft for the flight to be conducted. It is conducted by the pilot-in-command
Precipitation heat treatment A method of increasing the strength of heat-treated aluminum alloy. After the aluminum alloy has been solution-heat-treated by heating and quenching, it is returned to the oven and heated to a temperature lower than that used for the initial heat treatment. It is held at this temperature for a specified period of time, and then removed from the oven and allowed to cool slowly
Prepreg (preimpregnated fabric) A type of composite material in which the reinforcing fibers are encapsulated in an uncured resin. Prepreg materials must be kept refrigerated to prevent them from curing before they are used
Press-to-test light fixture An indicator light fixture whose lens can be pressed in to complete a circuit that tests the filament of the light bulb.
Pressure Force per unit area. Hydraulic and pneumatic pressure are normally given in units of pounds per square inch (psi)
Pressure altitude The altitude in standard air at which the pressure is the same as that of the existing air. Pressure altitude is read on an altimeter when the barometric scale is set to the standard sea level pressure of 29.92 inches of mercury
Pressure-demand oxygen system A type of oxygen system used by aircraft that fly at very high altitude. This system functions as a diluter-demand system until, at about 40,000 feet, the output to the mask is pressurized enough to force the needed oxygen into the lungs, rather than depending on the low pressure produced when the wearer of the mask inhales to pull in the oxygen. (See diluter-demand oxygen system.)
Pressure fueling The method of fueling used by almost all transport aircraft. The fuel is put into the aircraft through a single underwing fueling port. The fuel tanks are filled to the desired quantity and in the sequence selected by the person conducting the fueling operation. Pressure fueling saves servicing time by using a single point to fuel the entire aircraft, and it reduces the chances for fuel contamination
Pressure manifold (hydraulic system component) The portion of a fluid power system from which the selector valves receive their pressurized fluid.
Pressure plate (brake component) A strong, heavy plate used in a multiple-disk brake. The pressure plate receives the force from the brake cylinders and transmits this force to the disks
Pressure reducing valve (oxygen system component) A valve used in an oxygen system to change high cylinder pressure to low system pressure.
Pressure relief valve (oxygen system component) A valve in an oxygen system that relieves the pressure if the pressure reducing valve should fail.
Pressure vessel The strengthened portion of an aircraft structure that is sealed and pressurized in flight.
Primer (finishing system component) A component in a finishing system that provides a good bond between the surface and the material used for the topcoats.
Profile drag Aerodynamic drag produced by skin friction. Profile drag is a form of parasite drag
Progressive inspection An inspection that may be used in place of an annual or l00-hour inspection. It has the same scope as an annual inspection, but it may be performed in increments so the aircraft will not have to be out of service for a lengthy period of time
Pump control valve A control valve in a hydraulic system that allows the pilot to manually direct the output of the hydraulic pump back to the reservoir when no unit is being actuated.
Pureclad A registered trade name for clad aluminum alloy.
Purge (air conditioning system operation) To remove all of the moisture and air from a cooling system by flushing the system with a dry gaseous refrigerant.
Pusher powerplant A powerplant whose propeller is mounted at the rear of the airplane and pushes, rather than pulls, the airplane through the air.
PVC (Polyvinylchloride) A thermoplastic resin used to make transparent tubing for insulating electrical wires.
Quartersawed wood Wood sawed from a tree in such a way that the annual rings cross the plank at an angle greater than 45°.
Quick-disconnect fitting A hydraulic line fitting that seals the line when the fitting is disconnected. Quick-disconnect fittings are used on the lines connected to the engine-driven hydraulic pump. They allow the pump to be disconnected and an auxiliary hydraulic power system connected to perform checks requiring hydraulic power while the aircraft is in the hangar
Rack-and-pinion actuator A form of rotary actuator where the fluid acts on a piston on which a rack of gear teeth is cut. As the piston moves, it rotates a pinion gear which is mated with the teeth cut in the rack
Radial A directional line radiating outward from a radio facility, usually a VOR. When an aircraft is flying outbound on the 330° from the station
Radius dimpling A process of preparing a hole in sheet metal for flush riveting. A cone-shaped male die forces the edges of the rivet hole into the depression in a female die. Radius dimpling forms a round-edged depression into which the rivet head fits
Range markings Colored marks on an instrument dial that identify certain ranges of operation as specified in the aircraft maintenance or flight manual and listed in the appropriate aircraft Type Certificate Data Sheets or Aircraft Specifications. Color coding directs attention to approaching operating difficulties. Airspeed indicators and most pressure and temperature indicators are marked to show the various ranges of operation. These ranges and colors are the most generally used: Red radial line, do not exceed. Green arc, normal operating range. Yellow arc, caution range. Blue radial line, used on airspeed indicators to show best single- engine rate of climb speed. White arc, used on airspeed indicators to show flap operating range
RDF Radio direction finding.
Rebreather oxygen mask A type of oxygen mask used with a continuous flow oxygen system. Oxygen continuously flows into the bottom of the loose-fitting rebreather bag on the mask. The wearer of the mask exhales into the top of the bag. The first air exhaled contains some oxygen, and this air goes into the bag first. The last air to leave the lungs contains little oxygen, and it is forced out of the bag as the bag is filled with fresh oxygen. Each time the wearer of the mask inhales, the air first exhaled, along with fresh oxygen, is taken into the lungs
Receiver-dryer The component in a vapor-cycle cooling system that serves as a reservoir for the liquid refrigerant. The receiver-dryer contains a desiccant that absorbs any moisture that may be in the system
Rectangle A plane surface with four sides whose opposite sides are parallel and whose angles are all right angles.
Rectification (arc welding condition) A condition in AC- electric arc welding in which oxides on the surface of the metal act as a rectifier and prevent electrons flowing from the metal to the electrode during the half cycle when the electrode is positive.
Reducing flame See carburizing flame.
Reed valve A thin, leaf-type valve mounted in the valve plate of an air conditioning compressor to control the flow of refrigerant gases into and out of the compressor cylinders.
Reinforcing tape A narrow strip of woven fabric material placed over the fabric as it is being attached to the aircraft structure with rib lacing cord. This tape carries a large amount of the load and prevents the fabric tearing at the stitches
Rejuvenator A finishing material used to restore resilience to an old dope film. Rejuvenator contains strong solvents to open the dried-out film and plasticizers to restore resilience to the old dope
Relay An electrical component which uses a small amount of current flowing through a coil to produce a magnetic pull to close a set of contacts through which a large amount of current can flow. The core in a relay coil is fixed
Relief hole A hole drilled at the point at which two bend lines meet in a piece of sheet metal. This hole spreads the stresses caused by the bends and prevents the metal cracking
Relief valve A pressure-control valve that relieves any pressure over the amount for which it is set. They are damage- preventing units used in both hydraulic and pneumatic systems. In an aircraft hydraulic system, pressure relief valves prevent damaging high pressures that could be caused by a malfunctioning pressure regulator, or by thermal expansion of fluid trapped in portions of the system
Repair A maintenance procedure in which a damaged component is restored to its original condition, or at least to a condition that allows it to fulfill its design function.
Restrictor A fluid power system component that controls the rate of actuator movement by restricting the flow of fluid into or out of the actuator.
Retard breaker points A set of breaker points in certain aircraft magnetos that are used to provide a late (retarded) spark for starting the engine.
Retarder (finishing system component) Dope thinner that contains certain additives that slow its rate of evaporation enough to prevent dope blushing.
Retread The replacement of the tread rubber on an aircraft tire.
Retreating blade The blade on a helicopter rotor whose tip is moving in the direction opposite to that in which the helicopter is moving.
Retreating blade stall The stall of a helicopter rotor disc that occurs near the tip of the retreating blade. A retreating blade stall occurs when the flight airspeed is high and the retreating blade airspeed is low. This results in a high angle of attack, causing the stall
Return manifold The portion of a fluid power system through which the fluid is returned to the reservoir.
Reverse polarity welding DC-electric arc welding in which the electrode is positive with respect to the work.
Rib thread A series of circumferential grooves cut into the tread of a tire. This tread pattern provides superior traction and directional stability on hard-surfaced runways
Ribbon direction The direction in a piece of honeycomb material that is parallel to the length of the strips of material that make up the core.
Rigid conduit Aluminum alloy tubing used to house electrical wires in areas where they are subject to mechanical damage.
Rigidity in space The characteristic of a gyroscope that prevents its axis of rotation tilting as the earth rotates. This characteristic is used for attitude gyro instruments
Rime ice A rough ice that forms on aircraft flying through visible moisture, such as a cloud, when the temperature is below freezing. Rime ice disturbs the smooth airflow as well as adding weight
Rivet cutters Special cutting pliers that resemble diagonal cutters except that the jaws are ground in such a way that they cut the rivet shank, or stem, off square.
Rivet set A tool used to drive aircraft solid rivets. It is a piece of hardened steel with a recess the shape of the rivet head in one end. The other end fits into the rivet gun
Rocking shaft A shaft used in the mechanism of a pressure measuring instrument to change the direction of movement by 90° and to amplify the amount of movement.
Roll (aircraft maneuver) Rotation of an aircraft about its longitudinal axis.
Roots-type air compressor A positive-displacement air pump that uses two intermeshing figure-8-shaped rotors to move the air.
Rosette weld A method of securing one metal tube inside another by welding. Small holes are drilled in the outer tube and the inner tube is welded to it around the circumference of the holes
Rotary actuator A fluid power actuator whose output is rotational. A hydraulic motor is a rotary actuator
Roving A lightly twisted roll or strand of fibers.
RPM Revolutions per minute.
Ruddervator The two movable surfaces on a V-tail empennage. When these two surfaces are moved together with the in-and-out movement of the control yoke, they act as elevators, and when they are moved differentially with the rudder pedals, they act as the rudder
Saddle gusset A piece of plywood glued to an aircraft structural member. The saddle gusset has a cutout to hold a backing block or strip tightly against the skin to allow a nailing strip to be used to apply pressure to a glued joint in the skin
Sailplane A high-performance glider.
Sandwich material A type of composite structural material in which a core material is bonded between face sheets of metal or resin-impregnated fabric.
Satin-weave fabric Fabric in which the warp threads pass under one fill thread and over several others. Satin-weave fabrics are used when the lay-up must be made over complex shapes
Scarf joint A joint in a wood structure in which the ends to be joined are cut in a long taper, normally about l2:1, and fastened together by gluing. A glued scarf joint makes a strong splice because the joint is made along the side of the wood fibers rather than along their ends
Schematic diagram A diagram of an electrical system in which the system components are represented by symbols rather than drawings or pictures of the actual devices.
Schrader valve A type of service valve used in an air conditioning system. This is a spring-loaded valve much like the valve used to put air into a tire
Scissors A name commonly used for torque links. See torque links
Scupper A recess around the filler neck of an aircraft fuel tank. Any fuel spilled when the tank is being serviced collects in the scupper and drains to the ground through a drain line rather than flowing into the aircraft structure
Sector gear A part of a gear wheel containing the hub and a portion of the rim with teeth.
Series circuit A method of connecting electrical components in such a way that all the current flows through each of the components. There is only one path for current to flow
Series-parallel circuit An electrical circuit in which some of the components are connected in parallel and others are connected in series.
Selcal system Selective calling system. Each aircraft operated by an airline is assigned a particular four-tone audio combination for identification purposes. A ground station keys the signal whenever contact with that particular aircraft is desired. The signal is decoded by the airborne selcal decoder and the crew alerted by the selcal warning system
Selsyn system A DC synchro system used in remote indicating instruments. The rotor in the indicator is a permanent magnet and the stator is a tapped toroidal coil. The transmitter is a circular potentiometer with DC power fed into its wiper which is moved by the object being monitored. The transmitter is connected to the indicator in such a way that rotation of the transmitter shaft varies the current in the sections of the indicator toroidal coil. The magnet in the indicator on which the pointer is mounted locks with the magnetic field produced by the coils and follows the rotation of the transmitter shaft
Segmented-rotor brake A heavy-duty, multiple-disk brake used on large, high-speed aircraft. Stators that are surfaced with a material that retains its friction characteristics at high temperatures are keyed to the axle. Rotors which are keyed into the wheels mesh with the stators. The rotors are made in segments to allow for cooling and for their large amounts of expansion
Selector valve A flow control valve used in hydraulic systems that directs pressurized fluid into one side of an actuator, and at the same time directs return fluid from the other side of the actuator back to the reservoir. There are two basic types of selector valves: open-center valves and closed-center valves. The four-port closed-center valve is the most frequently used type. See closed-center selector valve and open-center selector valve
Selvage edge The woven edge of fabric used to prevent the material unraveling during normal handling. The selvage edge, which runs the length of the fabric parallel to the warp threads, is usually removed from materials used in composite construction
Semiconductor diode A two-element electrical component that allows current to pass through it in one direction, but blocks its passage in the opposite direction. A diode acts in an electrical system in the same way a check valve acts in a hydraulic system
Semimonocoque structure A form of aircraft stressed skin structure. Most of the strength of a semimonocoque structure is in the skin, but the skin is supported on a substructure of formers and stringers that give the skin its shape and increase its rigidity
Sensible heat Heat that is added to a liquid causing a change in its temperature but not its physical state.
Sensitivity A measure of the signal strength needed to produce a distortion-free output in a radio receiver.
Sequence valve A valve in a hydraulic system that requires a certain action to be completed before another action can begin. Sequence valves are used to assure that the hydraulically actuated wheel-well doors are completely open before pressure is directed to the landing gear to lower it
Servo An electrical or hydraulic actuator connected into a flight control system. A small force on the flight deck control is amplified by the servo and provides a large force to move the control surface
Servo amplifier An electronic amplifier in an autopilot system that increases the signal from the autopilot enough that it can operate the servos that move the control surfaces.
Servo tab A small movable tab built into the trailing edge of a primary control surface of an airplane. The flight deck controls move the tab in such a direction that it produces an aerodynamic force moving the surface on which it is mounted
Setback The distance the jaws of a brake must be set back from the mold line to form a bend. Setback for a 90° bend is equal to the inside radius of the bend plus the thickness of the metal being bent. For a bend other than 90°, a K-factor must be used. See also K-factor
Shake (wood defect) Longitudinal cracks in a piece of wood, usually between two annual rings.
SHF Super-high frequency.
Shear section A necked-down section of the drive shaft of a constant-displacement engine-driven fluid pump. If the pump should seize, the shear section will break and prevent the pump from being destroyed or the engine from being damaged. Some pumps use a shear pin rather than a shear section
Shear strength The strength of a riveted joint in a sheet metal structure in which the rivets shear before the metal tears at the rivet holes.
Shelf life The length of time a product is good when it remains in its original unopened container.
Shielded wire Electrical wire enclosed in a braided metal jacket. Electromagnetic energy radiated from the wire is trapped by the braid and is carried to ground
Shimmy Abnormal, and often violent, vibration of the nose wheel of an airplane. Shimmying is usually caused by looseness of the nose wheel support mechanism or an unbalanced wheel
Shimmy damper A small hydraulic shock absorber installed between the nose wheel fork and the nose wheel cylinder attached to the aircraft structure.
Shock mounts Resilient mounting pads used to protect electronic equipment by absorbing low-frequency, high amplitude vibrations.
Shock wave A pressure wave formed in the air by a flight vehicle moving at a speed greater than the speed of sound. As the vehicle passes through the air, it produces sound waves that spread out in all directions. But since the vehicle is flying faster than these waves are moving, they build up and form a pressure wave at the front and rear of the vehicle. As the air passes through a shock wave it slows down, its static pressure increases, and its total energy decreases
Shop head The head of a rivet which is formed when the shank is upset.
Show-type finish The type of finish put on fabric-covered aircraft intended for show. This finish is usually made up of many coats of dope, with much sanding and rubbing of the surface between coats
Shunt winding Field coils in an electric motor or generator that are connected in parallel with the armature.
Shuttle valve An automatic selector valve mounted on critical components such as landing gear actuation cylinders and brake cylinders. For normal operation, system fluid flows into the actuator through the shuttle valve, but if normal system pressure is lost, emergency system pressure forces the shuttle over and emergency fluid flows into the actuator
Sidestick controller A flight deck flight control used on some of the fly-by-wire equipped airplanes. The stick is mounted rigidly on the side console of the flight deck, and pressures exerted on the stick by the pilot produce electrical signals that are sent to the computer that flies the airplane
Sight glass (air conditioning system component) A small window in the high side of a vapor-cycle cooling system. Liquid refrigerant flows past the sight glass, and if the charge of refrigerant is low, bubbles will be seen. A fully charged system has no bubbles in the refrigerant
Sight line A line drawn on a sheet metal layout that is one bend radius from the bend-tangent line. The sight line is lined up directly below the nose of the radius bar in a cornice brake. When the metal is clamped in this position, the bend tangent line is in the correct position for the start of the bend
Silicon controlled rectifier (SCR) A semiconductor electron control device. An SCR blocks current flow in both directions until a pulse of positive voltage is applied to its gate. It then conducts in its forward direction, while continuing to block current in its reverse direction
Silicone rubber An elastomeric material made from silicone elastomers. Silicone rubber is compatible with fluids that attack other natural or synthetic rubbers
Single-acting actuator A linear hydraulic or pneumatic actuator that uses fluid power for movement in one direction and a spring force for its return.
Single-action hand pump A hand-operated fluid pump that moves fluid only during one stroke of the pump handle. One stroke pulls the fluid into the pump and the other forces the fluid out
Single-disk brakes Aircraft brakes in which a single steel disk rotates with the wheel between two brake-lining blocks. When the brake is applied, the disk is clamped tightly between the lining blocks, and the friction slows the aircraft
Single-servo brakes Brakes that uses the momentum of the aircraft rolling forward to help apply the brakes by wedging the brake shoe against the brake drum.
Sintered metal A porous material made by fusing powdered metal under heat and pressure.
Skydrol hydraulic fluid The registered trade name for a synthetic, nonflammable, phosphate ester-base hydraulic fluid used in modern high-temperature hydraulic systems.
Slat A secondary control on an aircraft that allows it to fly at a high angle of attack without stalling. A slat is a section of leading edge of wing mounted on curved tracks that move into and out of the wing on rollers
Slip roll former A shop tool used to form large radius curves on sheet metal.
Slippage mark A paint mark extending across the edge of an aircraft wheel onto a tube-type tire. When this mark is broken, it indicates the tire has slipped on the wheel, and there is a good reason to believe the tube has been damaged
Slipstream area For the purpose of rib stitch spacing, the slipstream area is considered to be the diameter of the propeller plus one wing rib on each side.
Slot (aerodynamic device) A fixed, nozzle-like opening near the leading edge of an airplane wing ahead of the aileron. A slot acts as a duct to force high-energy air down on the upper surface of the wing when the airplane is flying at a high angle of attack. The slot, which is located ahead of the aileron, causes the inboard portion of the wing to stall first, allowing the aileron to remain effective throughout the stall
Slow-blow fuse An electrical fuse that allows a large amount of current to flow for a short length of time but melts to open the circuit if more than its rated current flows for a longer period.
Smoke detector A device that warns the flight crew of the presence of smoke in cargo and/or baggage compartments. Some smoke detectors are of the visual type, others are photoelectric or ionization devices
Snubber A device in a hydraulic or pneumatic component that absorbs shock and/or vibration. A snubber is installed in the line to a hydraulic pressure gauge to prevent the pointer fluctuating
Softwood Wood from a tree that bears cones and has needles rather than leaves.
Soldering A method of thermally joining metal parts with a molten nonferrous alloy that melts at a temperature below 800 °F. The molten alloy is pulled up between close-fitting parts by capillary action. When the alloy cools and hardens, it forms a strong, leak-proof connection
Solenoid An electrical component using a small amount of current flowing through a coil to produce a magnetic force that pulls an iron core into the center of the coil. The core may be attached to a set of heavy-duty electrical contacts, or it may be used to move a valve or other mechanical device
Solidity (helicopter rotor characteristic) The solidity of a helicopter rotor system is the ratio of the total blade area to the disc area.
Solution heat treatment A type of heat treatment in which the metal is heated in a furnace until it has a uniform temperature throughout. It is then removed and quenched in cold water. When the metal is hot, the alloying elements enter into a solid solution with the base metal to become part of its basic structure. When the metal is quenched, these elements are locked into place
Sonic venture A venture in a line between a turbine engine or turbocharger and a pressurization system. When the air flowing through the venture reaches the speed of sound, a shock wave forms across the throat of the venture and limits the flow. A sonic venture is also called a flow limiter
Speciic heat The number of BTUs of heat energy needed to change the temperature of one pound of a substance 1 °F.
Speed brakes A secondary control of an airplane that produces drag without causing a change in the pitch attitude of the airplane. Speed brakes allow an airplane to make a steep descent without building up excessive forward airspeed
Spike knot A knot that runs through the depth of a beam perpendicular to the annual rings. Spike knots appear most frequently in quartersawed wood
Spin A flight maneuver in which an airplane descends in a corkscrew fashion. One wing is stalled and the other is producing lift
Spirit level A curved glass tube partially filled with a liquid, but with a bubble in it. When the device in which the tube is mounted is level, the bubble will be in the center of the tube
Splayed patch (wood structure repair) A type of patch made in an aircraft plywood structure in which the edges of the patch are tapered for approximately five times the thickness of the plywood. A splayed patch is not recommended for use on plywood less than 1/l0 inch thick
Split bus A type of electrical bus that allows all of the voltage-sensitive avionic equipment to be isolated from the rest of the aircraft electrical system when the engine is being started or when the ground-power unit is connected.
Split-rocker switch An electrical switch whose operating rocker is split so one half of the switch can be opened without affecting the other half. Split-rocker switches are used as aircraft master switches. The battery can be turned on without turning on the alternator, but the alternator cannot be turned on without also turning on the battery. The alternator can be turned off without turning off the battery, but the battery cannot be turned off without also turning off the alternator
Split (wood defect) A longitudinal crack in a piece of wood caused by externally induced stress.
Spoilers Flight controls that are raised up from the upper surface of a wing to destroy, or spoil, lift. Flight spoilers are used in conjunction with the ailerons to decrease lift and increase drag on the descending wing. Ground spoilers are used to produce a great amount of drag to slow the airplane on its landing roll
Spongy brakes Hydraulic brakes whose pedal has a spongy feel because of air trapped in the fluid.
Spontaneous combustion Self-ignition of a material caused by heat produced in the material as it combines with oxygen from the air.
Springwood The portion of an annual ring in a piece of wood formed principally during the first part of the growing season, the spring of the year. Springwood is softer, more porous, and lighter than the summerwood
Square A four-sided plane figure whose sides are all the same length, whose opposite sides are parallel, and whose angles are all right angles.
Squat switch An electrical switch actuated by the landing gear scissors on the oleo strut. When no weight is on the landing gear, the oleo piston is extended and the switch is in one position, but when weight is on the gear, the oleo strut compresses and the switch changes its position. Squat switches are used in antiskid brake systems, landing gear safety circuits, and cabin pressurization systems
Squib An explosive device in the discharge valve of a high-rate-discharge container of fire-extinguishing agent. The squib drives a cutter into the seal in the container to discharge the agent
SRM Structural Repair Manual.
Stabilator A flight control on the empennage of an airplane that acts as both a stabilizer and an elevator. The entire horizontal tail surface pivots and is moved as a unit
Stabilons Small wing-like horizontal surfaces mounted on the aft fuselage to improve longitudinal stability of airplanes that have an exceptionally wide center of gravity range.
Stagnation point The point on the leading edge of a wing at which the airflow separates, with some flowing over the top of the wing and the rest below the wing.
Stall strip A small triangular metal strip installed along the leading edge of an airplane wing near the wing root. Stall strips cause the root section of the wing to stall before the portion of the wing ahead of the ailerons
Standpipe A pipe sticking up in a tank or reservoir that allows part of the tank to be used as a reserve, or standby, source of fluid.
Starter-generator A single-component starter and generator used on many of the smaller gas-turbine engines. It is used as a starter, and when the engine is running, its circuitry is shifted so that it acts as a generator
Static Still, not moving.
Static air pressure Pressure of the ambient air surrounding the aircraft. Static pressure does not take into consideration any air movement
Static dischargers Devices connected to the trailing edges of control surfaces to discharge static electricity harmlessly into the air. They discharge the static charges before they can build up high enough to cause radio receiver interference
Stoddard solvent A petroleum product, similar to naphtha, used as a solvent and a cleaning fluid.
STOL Short takeoff and landing.
Stop drilling A method of stopping the growth of a crack in a piece of metal or transparent plastic by drilling a small hole at the end of the crack. The stresses are spread out all around the circumference of the hole rather than concentrated at the end of the crack
Straight polarity welding DC-electric arc welding in which the electrode is negative with respect to the work.
Strain A deformation or physical change in a material caused by a stress.
Stress A force set up within an object that tries to prevent an outside force from changing its shape.
Stressed skin structure A type of aircraft structure in which all or most of the stresses are carried in the outside skin. A stressed skin structure has a minimum of internal structure
Stress riser A location where the cross-sectional area of the part changes abruptly. Stresses concentrate at such a location and failure is likely. A scratch, gouge, or tool mark in the surface of a highly stressed part can change the area enough to concentrate the stresses and become a stress riser
Stringer A part of an aircraft structure used to give the fuselage its shape and, in some types of structure, to provide a small part of fuselage strength. Formers give the fuselage its cross-sectional shape and stringers fill in the shape between the formers
Stroboscopic tachometer A tachometer used to measure the speed of any rotating device without physical contact. A highly accurate variable-frequency oscillator triggers a high-intensity strobe light
Sublimation A process in which a solid material changes directly into a vapor without passing through the liquid stage.
Subsonic flight Flight at an airspeed in which all air flowing over the aircraft is moving at a speed below the speed of sound.
Summerwood The less porous, usually harder portion of an annual ring that forms in the latter part of the growing season, the summer of the year.
Sump A low point in an aircraft fuel tank in which water and other contaminants can collect and be held until they can be drained out.
Supercooled water Water in its liquid form at a temperature well below its natural freezing temperature. When supercooled water is disturbed, it immediately freezes
Superheat Heat energy that is added to a refrigerant after it changes from a liquid to a vapor.
Super heterodyne circuit A sensitive radio receiver circuit in which a local oscillator produces a frequency that is a specific difference from the received signal frequency. The desired signal and the output from the oscillator are mixed, and they produce a single, constant intermediate frequency. This IF is amplified, demodulated, and detected to produce the audio frequency that is used to drive the speaker
Supersonic flight Flight at an airspeed in which all air flowing over the aircraft is moving at a speed greater than the speed of sound.
Supplemental TC Certificate (STC) An approval issued by the TC for a modification to a type certificated airframe, engine, or component. More than one STC can be issued for the same basic alteration, but each holder must prove to the FAA that the alteration meets all the requirements of the original type certificate
Surface tape Strips of aircraft fabric that are doped over all seams and places where the fabric is stitched to the aircraft structure. Surface tape is also doped over the wing leading edges where abrasive wear occurs. The edges of surface tape are pink, or notched, to keep them from raveling before the dope is applied
Surfactant A surface active agent, or partially soluble contaminant, which is a by-product of fuel processing or of fuel additives. Surfactants adhere to other contaminants and cause them to drop out of the fuel and settle to the bottom of the fuel tank as sludge
Surveyor's transit An instrument consisting of a telescope mounted on a flat, graduated, circular plate on a tripod. The plate can be adjusted so it is level, and its graduations oriented to magnetic north. When an object is viewed through the telescope, its azimuth and elevation may be determined
Swashplate The component in a helicopter control system that consists basically of two bearing races with ball bearings between them. The lower, or nonrotating, race is tilted by the cyclic control, and the upper, or rotating, race has arms which connect to the control horns on the rotor blades. Movement of the cyclic pitch control is transmitted to the rotor blades through the swashplate. Movement of the collective pitch control raises or lowers the entire swashplate assembly to change the pitch of all the blades at the same time
Synchro system A remote instrument indicating system. A synchro transmitter is actuated by the device whose movement is to be measured, and it is connected electrically with wires to a synchro indicator whose pointer follows the movement of the shaft of the transmitter
Symmetrical airfoil An airfoil that has the same shape on both sides of its chord line, or center line.
Symmetry check A check of an airframe to determine that the wings and tail are symmetrical about the longitudinal axis.
System-pressure regulator (hydraulic system component) A type of hydraulic system-pressure control valve. When the system pressure is low, as it is when some unit is actuated, the output of the constant-delivery pump is directed into the system. When the actuation is completed and the pressure builds up to a specified kick-out pressure, the pressure regulator shifts. A check valve seals the system off and the pressure is maintained by the accumulator. The pump is unloaded and its output is directed back into the reservoir with very little opposition. The pump output pressure drops, but the volume of flow remains the same. When the system pressure drops to the specified kick-in pressure, the regulator again shifts and directs fluid into the system. Spool-type and balanced-pressure-type system pressure regulators are completely automatic in their operation and require no attention on the part of the flight crew
Tack coat A coat of finishing material sprayed on the surface and allowed to dry until the solvents evaporate. As soon as the solvents evaporate, a wet full-bodied coat of material is sprayed over it
Tack rag A clean, lintless rag, slightly damp with thinner. A tack rag is used to wipe a surface to prepare it to receive a coat of finishing material
Tack weld A method of holding parts together before they are permanently welded. The parts are assembled, and small spots of weld are placed at strategic locations to hold them in position
Tacky Slightly sticky to the touch.
Tailets Small vertical surfaces mounted underside of the horizontal stabilizer of some airplanes to increase the directional stability.
Takeoff warning system An aural warning system that provides audio warning signals when the thrust levers are advanced for takeoff if the stabilizer, flaps, or speed brakes are in an unsafe condition for takeoff.
Tang A tapered shank sticking out from the blade of a knife or a file. The handle of a knife or file is mounted on the tang
Teflon The registered trade name for a fluorocarbon resin used to make hydraulic and pneumatic seals, hoses, and backup rings.
Tempered glass Glass that has been heat-treated to increase its strength. Tempered glass is used in bird-proof, heated windshields for high-speed aircraft
Terminal strips A group of threaded studs mounted in a strip of insulating plastic. Electrical wires with crimped-on terminals are placed over the studs and secured with nuts
Terminal VOR A low-powered VOR that is normally located on an airport.
Tetraethyl lead (TEL) A heavy, oily, poisonous liquid, Pb(C2H5)4, that is mixed into aviation gasoline to increase its critical pressure and temperature.
Therapeutic mask adapter A calibrated orifice in the mask adapter for a continuous-flow oxygen system that increases the flow of oxygen to a mask being used by a passenger who is known to have a heart or respiratory problem.
Thermal dimpling See hot dimpling.
Thermal relief valve A relief valve in a hydraulic system that relieves pressure that builds up in an isolated part of the system because of heat. Thermal relief valves are set at a higher pressure than the system pressure relief valve
Thermistor A special form of electrical resistor whose resistance varies with its temperature.
Thermistor material A material with a negative temperature coefficient that causes its resistance to decrease as its temperature increases.
Thermocouple A loop consisting of two kinds of wire, joined at the hot, or measuring, junction and at the cold junction in the instrument. The voltage difference between the two junctions is proportional to the temperature difference between the junctions. In order for the current to be meaningful, the resistance of the thermocouple is critical, and the leads are designed for a specific installation. Their length should not be altered. Thermocouples used to measure cylinder head temperature are usually made of iron and constantan, and thermocouples that measure exhaust gas temperature for turbine engines are made of chromel and alumel
Thermocouple fire-detection system A fire-detection system that works on the principle of the rate-of-temperature rise. Thermocouples are installed around the area to be protected, and one thermocouple is surrounded by thermal insulation that prevents its temperature changing rapidly. In the event of a fire, the temperature of all the thermocouples except the protected one will rise immediately and a fire warning will be initiated. In the case of a general overheat condition, the temperature of all the thermocouples will rise uniformly and there will be no fire warning
Thermoplastic resin A type of plastic material that becomes soft when heated and hardens when cooled.
Thermosetting resin A type of plastic material that, when once hardened by heat, cannot be softened by being heated again.
Thermostatic expansion valve (TEV) The component in a vapor-cycle cooling system that meters the refrigerant into the evaporator. The amount of refrigerant metered by the TEV is determined by the temperature and pressure of the refrigerant as it leaves the evaporator coils. The TEV changes the refrigerant from a high-pressure liquid into a low-pressure liquid
Thixotropic agents Materials, such as microballoons, added to a resin to give it body and increase its workability.
TIG welding Tungsten inert welding is a form of electric arc welding in which the electrode is a nonconsumable tungsten wire. TIG welding is now called GTA (gas tungsten arc) welding
Toe-in A condition of landing gear alignment in which the front of the tires are closer together than the rear. When the aircraft rolls forward, the wheels try to move closer together
Toe-out A condition of landing gear alignment in which the front of the tires are further apart than the rear. When the aircraft rolls forward, the wheels try to move farther apart
Torque links The hinged link between the piston and cylinder of an oleo-type landing gear shock absorber. The torque links allow the piston to move freely in and out of the landing gear cylinder, but prevent it rotating. The torque links can be adjusted to achieve and maintain the correct wheel alignment. Torque links are also called scissors and nutcrackers
Torque tube A tube in an aircraft control system that transmits a torsional force from the operating control to the control surface.
Torsion rod A device in a spring tab to which the control horn is attached. For normal operation, the torsion rod acts as a fixed attachment point, but when the control surface loads are high, the torsion rod twists and allows the control horn to deflect the spring tab
Total air pressure The pressure a column of moving air will have if it is stopped.
TMC Thrust management computer.
Toroidal coil An electrical coil wound around a ring-shaped core of highly permeable material.
Total air temperature The temperature a column of moving air will have if it is stopped.
TR unit A transformer-rectifier unit. A TR unit reduces the voltage of AC and changes it into DC
Tractor powerplant An airplane powerplant in which the propeller is mounted in the front, and its thrust pulls the airplane rather than pushes it.
Trammel (verb) To square up the Pratt truss used in an airplane wing. Trammel points are set on the trammel bar so they measure the distance between the center of the front spar, at the inboard compression strut, and at the center of the rear spar at the next compression strut outboard. The drag and antidrug wires are adjusted until the distance between the center of the rear spar at the inboard compression strut and the center of the front spar at the next outboard compression strut is exactly the same as that between the first points measured
Trammel bar A wood or metal bar on which trammel points are mounted to compare distances.
Trammel points A set of sharp-pointed pins that protrude from the sides of a trammel bar.
Transducer A device that changes energy from one form to another. Commonly used transducers change mechanical movement or pressures into electrical signals
Transformer rectifier A component in a large aircraft electrical system used to reduce the AC voltage and change it into DC for charging the battery and for operating DC equipment in the aircraft.
Translational lift The additional lift produced by a helicopter rotor as the helicopter changes from hovering to forward flight.
Transonic flight Flight at an airspeed in which some air flowing over the aircraft is moving at a speed below the speed of sound, and other air is moving at a speed greater than the speed of sound.
Transverse pitch See gauge.
Triangle A three-sided, closed plane figure. The sum of the three angles in a triangle is always equal to l80°
Tricresyl phosphate (TCP) A chemical compound, (CH3C6H4O) 3PO, used in aviation gasoline to assist in scavenging the lead deposits left from the tetraethyl lead.
Trim tab A small control tab mounted on the trailing edge of a movable control surface. The tab may be adjusted to provide an aerodynamic force to hold the surface on which it is mounted deflected in order to trim the airplane for hands- off flight at a specified airspeed
Trimmed flight A flight condition in which the aerodynamic forces acting on the control surfaces are balanced and the aircraft is able to fly straight and level with no control input.
Trip-free circuit breaker A circuit breaker that opens a circuit any time an excessive amount of current flows, regardless of the position of the circuit breaker's operating handle.
Troubleshooting A procedure used in aircraft maintenance in which the operation of a malfunctioning system is analyzed to find the reason for the malfunction and to find a method for returning the system to its condition of normal operation.
True airspeed (TAS) Airspeed shown on the airspeed indicator (indicated airspeed) corrected for position error and nonstandard air temperature and pressure.
Trunnion Projections from the cylinder of a retractable landing gear strut about which the strut pivots retract.
Truss-type structure A type of structure made up of longitudinal beams and cross braces. Compression loads between the main beams are carried by rigid cross braces. Tension loads are carried by stays, or wires, that go from one main beam to the other and cross between the cross braces
Turbine A rotary device actuated by impulse or reaction of a fluid flowing through vanes or blades that are arranges around a central shaft.
Turn and slip indicator A rate gyroscopic flight instrument that gives the pilot an indication of the rate of rotation of the aircraft about its vertical axis. A ball in a curved glass tube shows the pilot the relationship between the centrifugal force and the force of gravity. This indicates whether or not the angle of bank is proper for the rate of turn. The turn and slip indicator shows the trim condition of the aircraft and serves as an emergency source of bank information in case the attitude gyro fails. Turn and slip indicators were formerly called needle and ball and turn and bank indicators
Turnbuckle A component in an aircraft control system used to adjust cable tension. A turnbuckle consists of a brass tubular barrel with right-hand threads in one end and left-hand in the other end. Control cable terminals screw into the two ends of the barrel, and turning the barrel pulls the terminals together, shortening the cable
Twist drill A metal cutting tool turned in a drill press or handheld drill motor. A twist drill has a straight shank and spiraled flutes. The cutting edge is ground on the end of the spiraled flutes
Twist rope A stripe of paint on flexible hose that runs the length of the hose. If this stripe spirals around the hose after it is installed, it indicates the hose was twisted when it was installed. Twist stripes are also called lay lines
Two-terminal spot-type fire detection system A fire detection system that uses individual thermoswitches installed around the inside of the area to be protected. These thermoswitches are wired in parallel between two separate circuits. A short or an open circuit can exist in either circuit without causing a fire warning
Type Certificate Data Sheets (TCDS) The official specifications of an aircraft, engine, or propeller issued by the Federal Aviation Administration. The TCDS lists pertinent specifications for the device, and it is the responsibility of the mechanic and/or inspector to ensure, on each inspection, that the device meets these specifications
Ultimate tensile strength The tensile strength required to cause a material to break or to continue to deform under a decreasing load.
Ultraviolet-blocking dope Dope that contains aluminum powder or some other pigment that blocks the passage of ultraviolet rays of the sun. The coat of dope protects the organic fabrics and clear dope from deterioration by these rays
Undamped oscillation Oscillation that continues with an unchanging amplitude once it has started.
Underslung rotor A helicopter rotor whose center of gravity is below the point at which it is attached to the mast.
Unidirectional fabric Fabric in which all the threads run in the same direction. These threads are often bound with a few fibers run at right angles, just enough to hold the yarns together and prevent their bunching
Unloading valve This is another name for system pressure regulator. See system pressure regulator
Utility finish The finish of an aircraft that gives the necessary tautness and fill to the fabric and the necessary protection to the metal, but does not have the glossy appearance of a show-type finish.
Vapor pressure The pressure of the vapor above a liquid needed to prevent the liquid evaporating. Vapor pressure is always specified at a specific temperature
Variable displacement pump A fluid pump whose output is controlled by the demands of the system. These pumps normally have a built-in system pressure regulator. When the demands of the system are low, the pump moves very little fluid, but when the demands are high, the pump moves a lot of fluid. Most variable displacement pumps used in aircraft hydraulic systems are piston-type pumps
Varnish (aircraft finishing material) A material used to produce an attractive and protective coating on wood or metal. Varnish is made of a resin dissolved in a solvent and thinned until it has the proper viscosity to spray or brush. The varnish is spread evenly over the surface to be coated, and when the solvents evaporate, a tough film is left
Varsol A petroleum product similar to naphtha used as a solvent and cleaning fluid.
Veneer Thin sheets of wood "peeled" from a log. A wide- blade knife held against the surface of the log peels away the veneer as the log is rotated in the cutter. Veneer is used for making plywood. Several sheets of veneer are glued together, with the grain of each sheet placed at 45° or 90° to the grain of the sheets next to it
Vertical fin The fixed vertical surface in the empennage of an airplane. The vertical fin acts as a weathervane to give the airplane directional stability
VHF Very high frequency.
Vibrator-type voltage regulator A type of voltage regulator used with a generator or alternator that intermittently places a resistance in the field circuit to control the voltage. A set of vibrating contacts puts the resistor in the circuit and takes it out several times a second
Viscosity The resistance of a fluid to flow. Viscosity refers to the "stiffness" of the fluid, or its internal friction
Viscosity cup A specially shaped cup with an accurately sized hole in its bottom. The cup is submerged in the liquid to completely fill it. It is then lifted from the liquid and the time in seconds is measured from the beginning of the flow through the hole until the first break in this flow. The viscosity of the liquid relates to this time
Vixen file A metal-cutting hand file that has curved teeth across its faces. Vixen files are used to remove large amounts of soft metal
Volatile liquid A liquid that easily changes into a vapor.
Voltmeter multiplier A precision resistor in series with a voltmeter mechanism used to extend the range of the basic meter or to allow a single meter to measure several ranges of voltage.
Vortex (plural vortices) A whirling motion in a fluid.
Vortex generator Small, low-aspect-ratio airfoils installed in pairs on the upper surface of a wing, on both sides of the vertical fin just ahead of the rudder, and on the underside of the vertical stabilizers of some airplanes. Their function is to pull high-energy air down to the surface to energize the boundary layer and prevent airflow separation until the surface reaches a higher angle of attack
Warp clock An alignment indicator included in a structural repair manual to show the orientation of the piles of a composite material. The ply direction is shown in relation to a reference direction
Warp threads Threads that run the length of the roll of fabric, parallel to the selvage edge. Warp threads are often stronger than fill threads
Warp tracers Threads of a different color from the warp threads that are woven into a material to identify the direction of the warp threads.
Wash in A twist in an airplane wing that increases its angle of incidence near the tip.
Wash out A twist in an airplane wing that decreases its angle of incidence near the tip.
Watt The basic unit of electrical power. One watt is equal to 1/746 horsepower
Web of a spar The part of a spar between the caps.
Weft threads See fill threads.
Wet-type vacuum pump An engine-driven air pump that uses steel vanes. These pumps are lubricated by engine oil drawn in through holes in the pump base. The oil passes through the pump and is exhausted with the air. Wet-type pumps must have oil separators in their discharge line to trap the oil and return it to the engine crankcase
Wing fences Vertical vanes that extend chordwise across the upper surface of an airplane wing to prevent spanwise airflow.
Wing heavy An out-of-trim flight condition in which an airplane flies hands off, with one wing low.
Wire bundle A compact group of electrical wires held together with special wrapping devices or with waxed string. These bundles are secured to the aircraft structure with special clamps
Woof threads See fill threads.
Work The product of force times distance.
Yaw Rotation of an aircraft about its vertical axis.
Yaw damper An automatic flight control system that counteracts the rolling and yawing produced by Dutch roll. See Dutch roll. A yaw damper senses yaw with a rate gyro and moves the rudder an amount proportional to the rate of yaw, but in the opposite direction
Yield strength The amount of stress needed to permanently deform a material.
Zener diode A special type of solid-state diode designed to have a specific breakdown voltage and to operate with current flowing through it in its reverse direction.
Zeppelin The name of large, rigid, lighter-than-air ships built by the Zeppelin Company in Germany prior to and during World War I.
Zero-center ammeter An ammeter in a light aircraft electrical system located between the battery and the main bus. This ammeter shows the current flowing into or out of the battery
100-hour inspection An inspection identical in scope to an annual inspection. Conducted every 100 hours of flight on aircraft of under 12,500 pounds that are used to carry passengers for hire
Absolute accuracy The ability to determine present position in space independently, and is most often used by pilots.
Absolute altitude The actual distance between an aircraft and the terrain over which it is flying.
Absolute pressure Pressure measured from the reference of zero pressure, or a vacuum.
AC Alternating current.
Acceleration Force involved in overcoming inertia, and which may be defined as a change in velocity per unit of time.
Acceleration error A magnetic compass error apparent when the aircraft accelerates while flying on an easterly or westerly heading, causing the compass card to rotate toward North.
Accelerate-go distance The distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and continue the takeoff on the remaining engine(s). The runway required includes the distance required to climb to 35 feet by which time V2 speed must be attained
Accelerate-stop distance The distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and abort the takeoff and bring the airplane to a stop using braking action only (use of thrust reversing is not considered).
Accelerometer A part of an inertial navigation system (INS) that accurately measures the force of acceleration in one direction.
ADC See air data computer.
ADF See automatic direction finder.
ADI See attitude director indicator.
Adiabatic cooling A process of cooling the air through expansion. For example, as air moves up slope it expands with the reduction of atmospheric pressure and cools as it expands
Adiabatic heating A process of heating dry air through compression. For example, as air moves down a slope it is compressed, which results in an increase in temperature
Adjustable-pitch propeller A propeller with blades whose pitch can be adjusted on the ground with the engine not running, but which cannot be adjusted in flight. Also referred to as a ground adjustable propeller. Sometimes also used to refer to constant-speed propellers that are adjustable in flight
Adjustable stabilizer A stabilizer that can be adjusted in flight to trim the airplane, thereby allowing the airplane to fly hands-off at any given airspeed.
ADM See aeronautical decision-making.
ADS-B See automatic dependent surveillance-broadcast.
Advection fog Fog resulting from the movement of warm, humid air over a cold surface.
Adverse yaw A condition of flight in which the nose of an airplane tends to yaw toward the outside of the turn. This is caused by the higher induced drag on the outside wing, which is also producing more lift. Induced drag is a by-product of the lift associated with the outside wing
Aerodynamics The science of the action of air on an object, and with the motion of air on other gases. Aerodynamics deals with the production of lift by the aircraft, the relative wind, and the atmosphere
Aeronautical chart A map used in air navigation containing all or part of the following: topographic features, hazards and obstructions, navigation aids, navigation routes, designated airspace, and airports.
Aeronautical decision-making (ADM) A systematic approach to the mental process used by pilots to consistently determine the best course of action in response to a given set of circumstances.
A/FD See Airport/Facility Directory.
Agonic line An irregular imaginary line across the surface of the Earth along which the magnetic and geographic poles are in alignment, and along which there is no magnetic variation.
Ailerons Primary flight control surfaces mounted on the trailing edge of an airplane wing, near the tip. Ailerons control roll about the longitudinal axis
Aircraft A device that is used, or intended to be used, for flight.
Aircraft altitude The actual height above sea level at which the aircraft is flying.
Aircraft approach category A performance grouping of aircraft based on a speed of 1.3 times the stall speed in the landing configuration at maximum gross landing weight
Air data computer (ADC) An aircraft computer that receives and processes pitot pressure, static pressure, and temperature to calculate very precise altitude, indicated airspeed, true airspeed, and air temperature.
Airfoil Any surface, such as a wing, propeller, rudder, or even a trim tab, which provides aerodynamic force when it interacts with a moving stream of air.
Air mass An extensive body of air having fairly uniform properties of temperature and moisture.
AIRMET Inflight weather advisory issued as an amendment to the area forecast, concerning weather phenomena of operational interest to all aircraft and that is potentially hazardous to aircraft with limited capability due to lack of equipment, instrumentation, or pilot qualifications.
Airplane An engine-driven, fixed-wing aircraft heavier than air that is supported in flight by the dynamic reaction of air against its wings.
Airplane Flight Manual (AFM) A document developed by the airplane manufacturer and approved by Transport Canada (TC). It is specific to a particular make and model airplane by serial number and it contains operating procedures and limitations
Airplane Owner/Information Manual A document developed by the airplane manufacturer containing general information about the make and model of an airplane. The airplane owner’s manual is not Transport Canada (TC) approved and is not specific to a particular serial numbered airplane. This manual is not kept current, and therefore cannot be substituted for the AFM/POH
Airport diagram The section of an instrument approach procedure chart that shows a detailed diagram of the airport. This diagram includes surface features and airport configuration information
Airport/Facility Directory (A/FD) An FAA publication containing information on all airports, communications, and NAVAIDs.
Airport surface detection equipment (ASDE) Radar equipment specifically designed to detect all principal features and traffic on the surface of an airport, presenting the entire image on the control tower console; used to augment visual observation by tower personnel of aircraft and/or vehicular movements on runways and taxiways.
Airport surveillance radar (ASR) Approach control radar used to detect and display an aircraft’s position in the terminal area.
Airport surveillance radar approach An instrument approach in which ATC issues instructions for pilot compliance based on aircraft position in relation to the final approach course and the distance from the end of the runway as displayed on the controller’s radar scope.
Air route surveillance radar (ARSR) Air route traffic control center (ARTCC) radar used primarily to detect and display an aircraft’s position while en route between terminal areas.
Air route traffic control center (ARTCC) Provides ATC service to aircraft operating on IFR flight plans within controlled airspace and principally during the en route phase of flight.
Airspeed Rate of the aircraft’s progress through the air.
Airspeed indicator A differential pressure gauge that measures the dynamic pressure of the air through which the aircraft is flying. Displays the craft’s airspeed, typically in knots, to the pilot
Air traffic control radar beacon system (ATCRBS) Sometimes called secondary surveillance radar (SSR), which utilizes a transponder in the aircraft. The ground equipment is an interrogating unit, in which the beacon antenna is mounted so it rotates with the surveillance antenna. The interrogating unit transmits a coded pulse sequence that actuates the aircraft transponder. The transponder answers the coded sequence by transmitting a preselected coded sequence back to the ground equipment, providing a strong return signal and positive aircraft identification, as well as other special data
Airway An airway is based on a centerline that extends from one navigation aid or intersection to another navigation aid (or through several navigation aids or intersections); used to establish a known route for en route procedures between terminal areas.
Certificate of Airworthiness (C of A) A certificate issued by the Transport Canada to all aircraft that have been proven to meet the minimum standards set down by the type certificate and CARS.
Airworthiness Directive A regulatory notice sent out by the FAA to the registered owner of an aircraft informing the owner of a condition that prevents the aircraft from continuing to meet its conditions for airworthiness. Airworthiness Directives (AD notes) are to be complied with within the required time limit, and the fact of compliance, the date of compliance, and the method of compliance are recorded in the aircraft’s maintenance records
Alert area An area in which there is a high volume of pilot training or an unusual type of aeronautical activity.
Almanac data Information the global positioning system (GPS) receiver can obtain from one satellite which describes the approximate orbital positioning of all satellites in the constellation. This information is necessary for the GPS receiver to know what satellites to look for in the sky at a given time
ALS See approach lighting system.
Alternate airport An airport designated in an IFR flight plan, providing a suitable destination if a landing at the intended airport becomes inadvisable.
Alternate static source valve A valve in the instrument static air system that supplies reference air pressure to the altimeter, airspeed indicator, and vertical speed indicator if the normal static pickup should become clogged or iced over.
Altimeter A flight instrument that indicates altitude by sensing pressure changes.
Altimeter setting Station pressure (the barometric pressure at the location the reading is taken) which has been corrected for the height of the station above sea level.
Altitude engine A reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.
Ambient pressure The pressure in the area immediately surrounding the aircraft.
Ambient temperature The temperature in the area immediately surrounding the aircraft.
AME See aviation medical examiner.
Amendment status The circulation date and revision number of an instrument approach procedure, printed above the procedure identification.
Ammeter An instrument installed in series with an electrical load used to measure the amount of current flowing through the load.
Aneroid barometer An instrument that measures the absolute pressure of the atmosphere by balancing the weight of the air above it against the spring action of the aneroid.
Anhedral A downward slant from root to tip of an aircraft’s wing or horizontal tail surface.
Annual inspection A complete inspection of an aircraft and engine, required by the Code of Federal Regulations, to be accomplished every 12 calendar months on all certificated aircraft. Only an A&P technician holding an Inspection Authorization can conduct an annual inspection
Anti-ice Preventing the accumulation of ice on an aircraft structure via a system designed for that purpose.
Approach lighting system (ALS) Provides lights that will penetrate the atmosphere far enough from touchdown to give directional, distance, and glidepath information for safe transition from instrument to visual flight.
Area chart Part of the low-altitude en route chart series, this chart furnishes terminal data at a larger scale for congested areas.
Area forecast (FA) A report that gives a picture of clouds, general weather conditions, and visual meteorological conditions (VMC) expected over a large area encompassing several states.
Area navigation (RNAV) Allows a pilot to fly a selected course to a predetermined point without the need to overfly ground-based navigation facilities, by using waypoints.
Arm See moment arm.
ARSR See Air route surveillance radar.
ASOS See Automated Surface Observing System. Aspect ratio. Span of a wing divided by its average chord. ASR. See airport surveillance radar
Asymmetric thrust ;Also known as P-factor. A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft’s longitudinal axis is in a climbing attitude in relation to the relative wind. The P-factor would be to the right if the aircraft had a counterclockwise rotating propeller.
ATC Air Traffic Control.
ATCRBS See air traffic control radar beacon system.
ATIS See automatic terminal information service.
Atmospheric propagation delay A bending of the electromagnetic (EM) wave from the satellite that creates an error in the GPS system.
Attitude A personal motivational predisposition to respond to persons, situations, or events in a given manner that can, nevertheless, be changed or modified through training as sort of a mental shortcut to decision-making.
Attitude and heading reference system (AHRS) A system composed of three-axis sensors that provide heading, attitude, and yaw information for aircraft. AHRS are designed to replace traditional mechanical gyroscopic flight instruments and provide superior reliability and accuracy
Attitude director indicator (ADI) An aircraft attitude indicator that incorporates flight command bars to provide pitch and roll commands.
Attitude instrument flying Controlling the aircraft by reference to the instruments rather than by outside visual cues.
Attitude management The ability to recognize hazardous attitudes in oneself and the willingness to modify them as necessary through the application of an appropriate antidote thought.
Autokinesis Nighttime visual illusion that a stationary light is moving, which becomes apparent after several seconds of staring at the light.
Automated Surface Observing System (ASOS) Weather reporting system which provides surface observations every minute via digitized voice broadcasts and printed reports.
Automated Weather Observing System (AWOS) Automated weather reporting system consisting of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast weather data.
Automatic dependent surveillance—broadcast (ADS-B) A device used in aircraft that repeatedly broadcasts a message that includes position (such as latitude, longitude, and altitude), velocity, and possibly other information.
Automatic direction finder (ADF) Electronic navigation equipment that operates in the low- and medium-frequency bands. Used in conjunction with the ground-based nondirectional beacon (NDB), the instrument displays the number of degrees clockwise from the nose of the aircraft to the station being received
Automatic terminal information service (ATIS) The continuous broadcast of recorded non-control information in selected terminal areas. Its purpose is to improve controller effectiveness and relieve frequency congestion by automating repetitive transmission of essential but routine information
Autopilot An automatic flight control system which keeps an aircraft in level flight or on a set course. Automatic pilots can be directed by the pilot, or they may be coupled to a radio navigation signal
Aviation medical examiner (AME) A physician with training in aviation medicine designated by the Civil Aerospace Medical Institute (CAMI).
Aviation Routine Weather Report (METAR) Observation of current surface weather reported in a standard international format.
AWOS See Automated Weather Observing System.
Axes of an aircraft Three imaginary lines that pass through an aircraft’s center of gravity. The axes can be considered as imaginary axles around which the aircraft rotates. The three axes pass through the center of gravity at 90° angles to each other. The axis from nose to tail is the longitudinal axis (pitch), the axis that passes from wingtip to wingtip is the lateral axis (roll), and the axis that passes vertically through the center of gravity is the vertical axis (yaw)
Axial flow compressor A type of compressor used in a turbine engine in which the airflow through the compressor is essentially linear. An axial-flow compressor is made up of several stages of alternate rotors and stators. The compressor ratio is determined by the decrease in area of the succeeding stages
Azimuth card A card that may be set, gyroscopically controlled, or driven by a remote compass.
Back course (BC) The reciprocal of the localizer course for an ILS. When flying a back-course approach, an aircraft approaches the instrument runway from the end at which the localizer antennas are installed
Baro-aiding A method of augmenting the GPS integrity solution by using a nonsatellite input source. To ensure that baro-aiding is available, the current altimeter setting must be entered as described in the operating manual
Basic empty weight (GAMA) Basic empty weight includes the standard empty weight plus optional and special equipment that has been installed.
BC See back course.
Biplanes Airplanes with two sets of wings.
Block altitude A block of altitudes assigned by ATC to allow altitude deviations; for example, “Maintain block altitude 9 to 11 thousand.”
Bypass ratio The ratio of the mass airflow in pounds per second through the fan section of a turbofan engine to the mass airflow that passes through the gas generator portion of the engine.
Cabin altitude Cabin pressure in terms of equivalent altitude above sea level.
Cage The black markings on the ball instrument indicating its neutral position.
Calibrated The instrument indication compared with a standard value to determine the accuracy of the instrument.
Calibrated orifice A hole of specific diameter used to delay the pressure change in the case of a vertical speed indicator.
Calibrated airspeed (CAS) The speed at which the aircraft is moving through the air, found by correcting IAS for instrument and position errors.
Camber The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing
Canard A horizontal surface mounted ahead of the main wing to provide longitudinal stability and control. It may be a fixed, movable, or variable geometry surface, with or without control surfaces
Canard configuration A configuration in which the span of the forward wings is substantially less than that of the main wing.
CAS See Calibrated airspeed.
Ceiling The height above the earth’s surface of the lowest layer of clouds, which is reported as broken or overcast, or the vertical visibility into an obscuration.
Center of gravity (CG) The point at which an airplane would balance if it were possible to suspend it at that point. It is the mass center of the airplane, or the theoretical point at which the entire weight of the airplane is assumed to be concentrated. It may be expressed in inches from the reference datum, or in percentage of mean aerodynamic chord (MAC). The location depends on the distribution of weight in the airplane
Center of gravity limits The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications
Center of gravity range The distance between the forward and aft CG limits indicated on pertinent airplane specifications.
Center of pressure A point along the wing chord line where lift is considered to be concentrated. For this reason, the center of pressure is commonly referred to as the center of lift
Centrifugal flow compressor An impeller-shaped device that receives air at its center and slings the air outward at high velocity into a diffuser for increased pressure. Also referred to as a radial outflow compressor
Centrifugal force An outward force that opposes centripetal force, resulting from the effect of inertia during a turn.
Centripetal force A center-seeking force directed inward toward the center of rotation created by the horizontal component of lift in turning flight.
CG See Center of gravity.
Changeover point (COP) A point along the route or airway segment between two adjacent navigation facilities or waypoints where changeover in navigation guidance should occur.
Checklist A tool that is used as a human factors aid in aviation safety. It is a systematic and sequential list of all operations that must be performed to properly accomplish a task
Chord line An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.
Circling approach A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straight- in landing from an instrument approach is not possible or is not desirable.
Class A airspace Airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 NM of the coast of the 48 contiguous states and Alaska; and designated international airspace beyond 12 NM of the coast of the 48 contiguous states and Alaska within areas of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied.
Class B airspace Airspace from the surface to 10,000 feet MSL surrounding the nation’s busiest airports in terms of IFR operations or passenger numbers. The configuration of each Class B airspace is individually tailored and consists of a surface area and two or more layers, and is designed to contain all published instrument procedures once an aircraft enters the airspace. For all aircraft, an ATC clearance is required to operate in the area, and aircraft so cleared receive separation services within the airspace
Class C airspace Airspace from the surface to 4,000 feet above the airport elevation (charted in MSL) surrounding those airports having an operational control tower, serviced by radar approach control, and having a certain number of IFR operations or passenger numbers. Although the configuration of each Class C airspace area is individually tailored, the airspace usually consists of a 5 NM radius core surface area that extends from the surface up to 4,000 feet above the airport elevation, and a 10 NM radius shelf area that extends from 1,200 feet to 4,000 feet above the airport elevation
Class D airspace Airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower. The configuration of each Class D airspace area is individually tailored, and when instrument procedures are published, the airspace is normally designed to contain the procedures
Class E airspace Airspace that is not Class A, Class B, Class C, or Class D, and is controlled airspace.
Class G airspace Airspace that is uncontrolled, except when associated with a temporary control tower, and has not been designated as Class A, Class B, Class C, Class D, or Class E airspace.
Clean configuration A configuration in which all flight control surfaces have been placed to create minimum drag. In most aircraft this means flaps and gear retracted
Clearance ATC permission for an aircraft to proceed under specified traffic conditions within controlled airspace, for the purpose of providing separation between known aircraft.
Clearance delivery Control tower position responsible for transmitting departure clearances to IFR flights.
Clearance limit The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance.
Clearance on request An IFR clearance not yet received after filing a flight plan.
Clearance void time Used by ATC, the time at which the departure clearance is automatically canceled if takeoff has not been made. The pilot must obtain a new clearance or cancel the IFR flight plan if not off by the specified time
Clear ice Glossy, clear, or translucent ice formed by the relatively slow freezing of large, supercooled water droplets.
Cold front The boundary between two air masses where cold air is replacing warm air.
Compass course A true course corrected for variation and deviation errors.
Compass locator A low-power, low- or medium-frequency (L/MF) radio beacon installed at the site of the outer or middle marker of an ILS.
Complex aircraft An aircraft with retractable landing gear, flaps, and a controllable pitch propeller.
Compressor pressure ratio The ratio of compressor discharge pressure to compressor inlet pressure.
Compressor stall In gas turbine engines, a condition in an axial-flow compressor in which one or more stages of rotor blades fail to pass air smoothly to the succeeding stages. A stall condition is caused by a pressure ratio that is incompatible with the engine rpm. Compressor stall will be indicated by a rise in exhaust temperature or rpm fluctuation, and if allowed to continue, may result in flameout and physical damage to the engine
Computer navigation fix A point used to define a navigation track for an airborne computer system such as GPS or FMS.
Concentric rings Dashed-line circles depicted in the plan view of IAP charts, outside of the reference circle, that show en route and feeder facilities.
Condensation A change of state of water from a gas (water vapor) to a liquid.
Condensation nuclei Small particles of solid matter in the air on which water vapor condenses.
Cone of confusion A cone-shaped volume of airspace directly above a VOR station where no signal is received, causing the CDI to fluctuate.
Configuration This is a general term, which normally refers to the position of the landing gear and flaps.
Constant-speed propeller A controllable-pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant rpm in spite of varying air loads.
Continuous flow oxygen system System that supplies a constant supply of pure oxygen to a rebreather bag that dilutes the pure oxygen with exhaled gases and thus supplies a healthy mix of oxygen and ambient air to the mask. Primarily used in passenger cabins of commercial airliners
Control and performance A method of attitude instrument flying in which one instrument is used for making attitude changes, and the other instruments are used to monitor the progress of the change.
Control display unit A display interfaced with the master computer, providing the pilot with a single control point for all navigations systems, thereby reducing the number of required flight deck panels.
Controllability A measure of the response of an aircraft relative to the pilot’s flight control inputs.
Controlled airspace An airspace of defined dimensions within which ATC service is provided to IFR and VFR flights in accordance with the airspace classification. It includes Class A, Class B, Class C, Class D, and Class E airspace
Control pressures The amount of physical exertion on the control column necessary to achieve the desired attitude.
Convective weather Unstable, rising air found in cumiliform clouds.
Convective SIGMET Weather advisory concerning convective weather significant to the safety of all aircraft, including thunderstorms, hail, and tornadoes.
Conventional landing gear Landing gear employing a third rear-mounted wheel. These airplanes are also sometimes referred to as tailwheel airplanes
Coordinated flight Flight with a minimum disturbance of the forces maintaining equilibrium, established via effective control use.
COP See changeover point.
Coriolis illusion The illusion of rotation or movement in an entirely different axis, caused by an abrupt head movement, while in a prolonged constant-rate turn that has ceased to stimulate the brain’s motion sensing system.
Coupled ailerons and rudder Rudder and ailerons are connected with interconnected springs in order to counteract adverse yaw. Can be overridden if it becomes necessary to slip the aircraft
Course The intended direction of flight in the horizontal plane measured in degrees from north.
Cowl flaps Shutter-like devices arranged around certain air-cooled engine cowlings, which may be opened or closed to regulate the flow of air around the engine.
Crew resource management (CRM) The application of team management concepts in the flight deck environment. It was initially known as cockpit resource management, but as CRM programs evolved to include cabin crews, maintenance personnel, and others, the phrase “crew resource management” was adopted. This includes single pilots, as in most general aviation aircraft. Pilots of small aircraft, as well as crews of larger aircraft, must make effective use of all available resources; human resources, hardware, and information. A current definition includes all groups routinely working with the flight crew who are involved in decisions required to operate a flight safely. These groups include, but are not limited to pilots, dispatchers, cabin crewmembers, maintenance personnel, and air traffic controllers. CRM is one way of addressing the challenge of optimizing the human/machine interface and accompanying interpersonal activities
Critical altitude The maximum altitude under standard atmospheric conditions at which a turbocharged engine can produce its rated horsepower.
Critical angle of attack The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight.
Critical areas Areas where disturbances to the ILS localizer and glideslope courses may occur when surface vehicles or aircraft operate near the localizer or glideslope antennas.
CRM See crew resource management.
Cross-check The first fundamental skill of instrument flight, also known as “scan,” the continuous and logical observation of instruments for attitude and performance information.
Cruise clearance An ATC clearance issued to allow a pilot to conduct flight at any altitude from the minimum IFR altitude up to and including the altitude specified in the clearance. Also authorizes a pilot to proceed to and make an approach at the destination airport
Current induction An electrical current being induced into, or generated in, any conductor that is crossed by lines of flux from any magnet.
DA See Decision altitude.
Datum (Reference Datum) An imaginary vertical plane or line from which all measurements of arm are taken. The datum is established by the manufacturer. Once the datum has been selected, all moment arms and the location of CG range are measured from this point
DC See Direct current
Dark adaptation Physical and chemical adjustments of the eye that make vision possible in relative darkness.
Dead reckoning Navigation of an airplane solely by means of computations based on airspeed, course, heading, wind direction and speed, groundspeed, and elapsed time.
Deceleration error A magnetic compass error that occurs when the aircraft decelerates while flying on an easterly or westerly heading, causing the compass card to rotate toward South.
Decision altitude (DA) A specified altitude in the precision approach, charted in feet MSL, at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.
Decision height (DH) A specified altitude in the precision approach, charted in height above threshold elevation, at which a decision must be made either to continue the approach or to execute a missed approach.
Deice The act of removing ice accumulation from an aircraft structure.
Delta A Greek letter expressed by the symbol ? to indicate a change of values. As an example, ?CG indicates a change (or movement) of the CG
Density altitude Pressure altitude corrected for nonstandard temperature. Density altitude is used in computing the performance of an aircraft and its engines
Departure procedure (DP) Preplanned IFR ATC departure, published for pilot use, in textual and graphic format.
Deposition The direct transformation of a gas to a solid state, in which the liquid state is bypassed. Some sources use sublimation to describe this process instead of deposition
Deviation A magnetic compass error caused by local magnetic fields within the aircraft. Deviation error is different on each heading
Dew Moisture that has condensed from water vapor. Usually found on cooler objects near the ground, such as grass, as the near-surface layer of air cools faster than the layers of air above it
Dewpoint The temperature at which air reaches a state where it can hold no more water.
DGPS Differential global positioning system.
DH See Decision height.
Differential ailerons Control surface rigged such that the aileron moving up moves a greater distance than the aileron moving down. The up aileron produces extra parasite drag to compensate for the additional induced drag caused by the down aileron. This balancing of the drag forces helps minimize adverse yaw
Differential Global Positioning System (DGPS) A system that improves the accuracy of Global Navigation Satellite Systems (GNSS) by measuring changes in variables to provide satellite positioning corrections.
Direct indication The true and instantaneous reflection of aircraft pitch-and-bank attitude by the miniature aircraft, relative to the horizon bar of the attitude indicator.
Direct User Access Terminal System (DUATS) A system that provides current FAA weather and flight plan filing services to certified civil pilots, via personal computer, modem, or telephone access to the system. Pilots can request specific types of weather briefings and other pertinent data for planned flights
Directional stability Stability about the vertical axis of an aircraft, whereby an aircraft tends to return, on its own, to flight aligned with the relative wind when disturbed from that equilibrium state. The vertical tail is the primary contributor to directional stability, causing an airplane in flight to align with the relative wind
Distance circle See Reference circle.
Distance measuring equipment (DME) A pulse-type electronic navigation system that shows the pilot, by an instrument-panel indication, the number of nautical miles between the aircraft and a ground station or waypoint.
DME arc A flight track that is a constant distance from the station or waypoint.
DOD Department of Defense.
Doghouse A turn-and-slip indicator dial mark in the shape of a doghouse.
Domestic Reduced Vertical Separation Minimum (DRVSM) Additional flight levels between FL 290 and FL 410 to provide operational, traffic, and airspace efficiency.
Double gimbal A type of mount used for the gyro in an attitude instrument. The axes of the two gimbals are at right angles to the spin axis of the gyro, allowing free motion in two planes around the gyro
DP See departure procedure.
Drag The net aerodynamic force parallel to the relative wind, usually the sum of two components: induced drag and parasite drag.
Drag curve The curve created when plotting induced drag and parasite drag.
Drift angle Angle between heading and track.
DRVSM See Domestic Reduced Vertical Separation Minimum.
DUATS See direct user access terminal system.
Duplex Transmitting on one frequency and receiving on a separate frequency.
Dynamic hydroplaning A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective anti-skid system can minimize the effects of hydroplaning
Eddy currents Current induced in a metal cup or disc when it is crossed by lines of flux from a moving magnet.
EFAS See En Route Flight Advisory Service.
EFC See expect-further-clearance. EFD. See electronic flight display. EGT. See exhaust gas temperature
Electronic flight display (EFD) For the purpose of standardization, any flight instrument display that uses LCD or other image-producing system (cathode ray tube (CRT), etc.)
Elevator The horizontal, movable primary control surface in the tail section, or empennage, of an airplane. The elevator is hinged to the trailing edge of the fixed horizontal stabilizer
Elevator illusion The sensation of being in a climb or descent, caused by the kind of abrupt vertical accelerations that result from up- or downdrafts.
Emergency A distress or urgent condition.
Empennage The section of the airplane that consists of the vertical stabilizer, the horizontal stabilizer, and the associated control surfaces.
Emphasis error The result of giving too much attention to a particular instrument during the cross-check, instead of relying on a combination of instruments necessary for attitude and performance information.
Empty-field myopia Induced nearsightedness that is associated with flying at night, in instrument meteorological conditions and/or reduced visibility. With nothing to focus on, the eyes automatically focus on a point just slightly ahead of the airplane
EM wave Electromagnetic wave.
Encoding altimeter A special type of pressure altimeter used to send a signal to the air traffic controller on the ground, showing the pressure altitude the aircraft is flying.
Engine pressure ratio (EPR) The ratio of turbine discharge pressure divided by compressor inlet pressure, which is used as an indication of the amount of thrust being developed by a turbine engine.
En route facilities ring Depicted in the plan view of IAP charts, a circle which designates NAVAIDs, fixes, and intersections that are part of the en route low altitude airway structure.
En Route Flight Advisory Service (EFAS) An en route weather-only AFSS service.
En route high-altitude charts Aeronautical charts for en route instrument navigation at or above 18,000 feet MSL.
En route low-altitude charts Aeronautical charts for en route IFR navigation below 18,000 feet MSL.
EPR See engine pressure ratio.
Equilibrium A condition that exists within a body when the sum of the moments of all of the forces acting on the body is equal to zero. In aerodynamics, equilibrium is when all opposing forces acting on an aircraft are balanced (steady, unaccelerated flight conditions)
Equivalent airspeed Airspeed equivalent to CAS in standard atmosphere at sea level. As the airspeed and pressure altitude increase, the CAS becomes higher than it should be, and a correction for compression must be subtracted from the CAS
Evaporation The transformation of a liquid to a gaseous state, such as the change of water to water vapor.
Exhaust gas temperature (EGT) The temperature of the exhaust gases as they leave the cylinders of a reciprocating engine or the turbine section of a turbine engine.
Expect-further-clearance (EFC) The time a pilot can expect to receive clearance beyond a clearance limit.
Explosive decompression A change in cabin pressure faster than the lungs can decompress. Lung damage is possible
FA See area forecast.
CARS See Canadian Aviation Regulations
FAF See final approach fix.
False horizon Inaccurate visual information for aligning the aircraft, caused by various natural and geometric formations that disorient the pilot from the actual horizon.
FDI See flight director indicator.
Federal airways Class E airspace areas that extend upward from 1,200 feet to, but not including, 18,000 feet MSL, unless otherwise specified.
Feeder facilities Used by ATC to direct aircraft to intervening fixes between the en route structure and the initial approach fix.
Final approach Part of an instrument approach procedure in which alignment and descent for landing are accomplished.
Final approach fix (FAF) The fix from which the IFR final approach to an airport is executed, and which identifies the beginning of the final approach segment. An FAF is designated on government charts by a Maltese cross symbol for nonprecision approaches, and a lightning bolt symbol for precision approaches
Fixating Staring at a single instrument, thereby interrupting the cross-check process.
Fixed-pitch propellers Propellers with fixed blade angles. Fixed-pitch propellers are designed as climb propellers, cruise propellers, or standard propellers
Fixed slot A fixed, nozzle shaped opening near the leading edge of a wing that ducts air onto the top surface of the wing. Its purpose is to increase lift at higher angles of attack
FL See flight level.
Flameout A condition in the operation of a gas turbine engine in which the fire in the engine goes out due to either too much or too little fuel sprayed into the combustors.
Flaps Hinged portion of the trailing edge between the ailerons and fuselage. In some aircraft ailerons and flaps are interconnected to produce full-span “flaperons.” In either case, flaps change the lift and drag on the wing
Floor load limit The maximum weight the floor can sustain per square inch/foot as provided by the manufacturer.
Flight configurations Adjusting the aircraft control surfaces (including flaps and landing gear) in a manner that will achieve a specified attitude.
Flight director indicator (FDI) One of the major components of a flight director system, it provides steering commands that the pilot (or the autopilot, if coupled) follows.
Flight level (FL) A measure of altitude (in hundreds of feet) used by aircraft flying above 18,000 feet with the altimeter set at 29.92 "Hg
Flight management system (FMS) Provides pilot and crew with highly accurate and automatic long-range navigation capability, blending available inputs from long- and short- range sensors.
Flight path The line, course, or track along which an aircraft is flying or is intended to be flown.
Flight patterns Basic maneuvers, flown by reference to the instruments rather than outside visual cues, for the purpose of practicing basic attitude flying. The patterns simulate maneuvers encountered on instrument flights such as holding patterns, procedure turns, and approaches
Flight strips Paper strips containing instrument flight information, used by ATC when processing flight plans.
FMS See flight management system.
FOD See foreign object damage.
Fog Cloud consisting of numerous minute water droplets and based at the surface; droplets are small enough to be suspended in the earth’s atmosphere indefinitely. (Unlike drizzle, it does not fall to the surface. Fog differs from a cloud only in that a cloud is not based at the surface, and is distinguished from haze by its wetness and gray color.)
Force (F) The energy applied to an object that attempts to cause the object to change its direction, speed, or motion. In aerodynamics, it is expressed as F, T (thrust), L (lift), W (weight), or D (drag), usually in pounds
Foreign object damage (FOD) Damage to a gas turbine engine caused by some object being sucked into the engine while it is running. Debris from runways or taxiways can cause foreign object damage during ground operations, and the ingestion of ice and birds can cause FOD in flight
Form drag The drag created because of the shape of a component or the aircraft.
Frise-type aileron Aileron having the nose portion projecting ahead of the hinge line. When the trailing edge of the aileron moves up, the nose projects below the wing’s lower surface and produces some parasite drag, decreasing the amount of adverse yaw
Front The boundary between two different air masses.
Fuel load The expendable part of the load of the airplane. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps
Fundamental skills Pilot skills of instrument cross-check, instrument interpretation, and aircraft control.
Fuselage The section of the airplane that consists of the cabin and/or cockpit, containing seats for the occupants and the controls for the airplane.
GAMA General Aviation Manufacturers Association.
Gimbal ring A type of support that allows an object, such as a gyroscope, to remain in an upright condition when its base is tilted.
Glideslope (GS) Part of the ILS that projects a radio beam upward at an angle of approximately 3° from the approach end of an instrument runway. The glideslope provides vertical guidance to aircraft on the final approach course for the aircraft to follow when making an ILS approach along the localizer path
Glideslope intercept altitude The minimum altitude of an intermediate approach segment prescribed for a precision approach that ensures obstacle clearance.
Global landing system (GLS) An instrument approach with lateral and vertical guidance with integrity limits (similar to barometric vertical navigation (BARO VNAV).
Global navigation satellite system (GNSS) Satellite navigation system that provides autonomous geospatial positioning with global coverage. It allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few meters using time signals transmitted along a line of sight by radio from satellites
Global positioning system (GPS) Navigation system that uses satellite rather than ground-based transmitters for location information.
GLS See global landing system.
GNSS See global navigation satellite system.
Goniometer As used in radio frequency (RF) antenna systems, a direction-sensing device consisting of two fixed loops of wire oriented 90° from each other, which separately sense received signal strength and send those signals to two rotors (also oriented 90°) in the sealed direction-indicating instrument. The rotors are attached to the direction-indicating needle of the instrument and rotated by a small motor until minimum magnetic field is sensed near the rotors
GPS See global positioning system.
GPS Approach Overlay Program An authorization for pilots to use GPS avionics under IFR for flying designated existing nonprecision instrument approach procedures, with the exception of LOC, LDA, and SDF procedures.
GPWS See ground proximity warning system.
Graveyard spiral The illusion of the cessation of a turn while still in a prolonged, coordinated, constant rate turn, which can lead a disoriented pilot to a loss of control of the aircraft.
Great circle route The shortest distance across the surface of a sphere (the Earth) between two points on the surface.
Ground adjustable trim tab Non-movable metal trim tab on a control surface. Bent in one direction or another while on the ground to apply trim forces to the control surface
Ground effect The condition of slightly increased air pressure below an airplane wing or helicopter rotor system that increases the amount of lift produced. It exists within approximately one wing span or one rotor diameter from the ground. It results from a reduction in upwash, downwash, and wingtip vortices, and provides a corresponding decrease in induced drag
Ground proximity warning system (GPWS) A system designed to determine an aircraft’s clearance above the Earth and provides limited predictability about aircraft position relative to rising terrain.
Groundspeed Speed over the ground, either closing speed to the station or waypoint, or speed over the ground in whatever direction the aircraft is going at the moment, depending upon the navigation system used.
GS See glideslope.
GWPS See ground proximity warning system.
HAA See height above airport.
HAL See height above landing.
HAT See height above touchdown elevation.
Hazardous attitudes Five aeronautical decision-making attitudes that may contribute to poor pilot judgment: anti- authority, impulsivity, invulnerability, machismo, and resignation.
Hazardous Inflight Weather Advisory Service (HIWAS) Service providing recorded weather forecasts broadcast to airborne pilots over selected VORs.
Head-up display (HUD) A special type of flight viewing screen that allows the pilot to watch the flight instruments and other data while looking through the windshield of the aircraft for other traffic, the approach lights, or the runway.
Heading The direction in which the nose of the aircraft is pointing during flight.
Heading indicator An instrument which senses airplane movement and displays heading based on a 360° azimuth, with the final zero omitted. The heading indicator, also called a directional gyro (DG), is fundamentally a mechanical instrument designed to facilitate the use of the magnetic compass. The heading indicator is not affected by the forces that make the magnetic compass difficult to interpret
Headwork Required to accomplish a conscious, rational thought process when making decisions. Good decision- making involves risk identification and assessment, information processing, and problem solving
Height above airport (HAA) The height of the MDA above the published airport elevation.
Height above landing (HAL) The height above a designated helicopter landing area used for helicopter instrument approach procedures.
Height above touchdown elevation (HAT) The DA/DH or MDA above the highest runway elevation in the touchdown zone (first 3,000 feet of the runway).
HF High frequency.
Hg Abbreviation for mercury, from the Latin hydrargyrum.
High performance aircraft An aircraft with an engine of more than 200 horsepower.
Histotoxic hypoxia The inability of cells to effectively use oxygen. Plenty of oxygen is being transported to the cells that need it, but they are unable to use it
HIWAS See Hazardous Inflight Weather Advisory Service.
Holding A predetermined maneuver that keeps aircraft within a specified airspace while awaiting further clearance from ATC.
Holding pattern A racetrack pattern, involving two turns and two legs, used to keep an aircraft within a prescribed airspace with respect to a geographic fix. A standard pattern uses right turns; nonstandard patterns use left turns
Homing Flying the aircraft on any heading required to keep the needle pointing to the 0° relative bearing position.
Horizontal situation indicator (HSI) A flight navigation instrument that combines the heading indicator with a CDI, in order to provide the pilot with better situational awareness of location with respect to the courseline.
Horsepower The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute
Hot start In gas turbine engines, a start which occurs with normal engine rotation, but exhaust temperature exceeds prescribed limits. This is usually caused by an excessively rich mixture in the combustor. The fuel to the engine must be terminated immediately to prevent engine damage
HUD See head-up display.
Human factors A multidisciplinary field encompassing the behavioral and social sciences, engineering, and physiology, to consider the variables that influence individual and crew performance for the purpose of optimizing human performance and reducing errors.
Hung start In gas turbine engines, a condition of normal light off but with rpm remaining at some low value rather than increasing to the normal idle rpm. This is often the result of insufficient power to the engine from the starter. In the event of a hung start, the engine should be shut down
Hydroplaning A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective anti-skid system can minimize the effects of hydroplaning
Hypemic hypoxia A type of hypoxia that is a result of oxygen deficiency in the blood, rather than a lack of inhaled oxygen. It can be caused by a variety of factors. Hypemic means “not enough blood.”
Hyperventilation Occurs when an individual is experiencing emotional stress, fright, or pain, and the breathing rate and depth increase, although the carbon dioxide level in the blood is already at a reduced level. The result is an excessive loss of carbon dioxide from the body, which can lead to unconsciousness due to the respiratory system’s overriding mechanism to regain control of breathing
Hypoxic hypoxia This type of hypoxia is a result of insufficient oxygen available to the lungs. A decrease of oxygen molecules at sufficient pressure can lead to hypoxic hypoxia
IAF See initial approach fix.
IAP See instrument approach procedures.
IAS See indicated airspeed.
ICAO See International Civil Aviation Organization.
Ident Air Traffic Control request for a pilot to push the button on the transponder to identify return on the controller’s scope.
IFR See Instrument flight rules.
ILS See instrument landing system.
IMC See instrument meteorological conditions.
Inclinometer An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn
Indicated airspeed (IAS) Shown on the dial of the instrument airspeed indicator on an aircraft. Indicated airspeed (IAS) is the airspeed indicator reading uncorrected for instrument, position, and other errors. Indicated airspeed means the speed of an aircraft as shown on its pitot static airspeed indicator calibrated to reflect standard atmosphere adiabatic compressible flow at sea level uncorrected for airspeed system errors. Calibrated airspeed (CAS) is IAS corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors
Indicated altitude The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
Indirect indication A reflection of aircraft pitch-and-bank attitude by instruments other than the attitude indicator.
Induction icing A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing
Inertial navigation system (INS) Inertial navigation system (INS). A computer-based navigation system that tracks the movement of an aircraft via signals produced by onboard accelerometers. The initial location of the aircraft is entered into the computer, and all subsequent movement of the aircraft is sensed and used to keep the position updated. An INS does not require any inputs from outside signals.
Initial approach fix (IAF) The fix depicted on IAP charts where the instrument approach procedure (IAP) begins unless otherwise authorized by ATC.
Inoperative components Higher minimums are prescribed when the specified visual aids are not functioning; this information is listed in the Inoperative Components Table found in the United States Terminal Procedures Publications.
Instantaneous vertical speed indicator (IVSI) Assists in interpretation by instantaneously indicating the rate of climb or descent at a given moment with little or no lag as displayed in a vertical speed indicator (VSI).
Instrument approach procedures (IAP) A series of predetermined maneuvers for the orderly transfer of an aircraft under IFR from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.
Instrument flight rules (IFR) Rules and regulations established by the Federal Aviation Administration to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals
Instrument landing system (ILS) An electronic system that provides both horizontal and vertical guidance to a specific runway, used to execute a precision instrument approach procedure.
Instrument meteorological conditions (IMC) Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums specified for visual meteorological conditions, requiring operations to be conducted under IFR.
Instrument takeoff Using the instruments rather than outside visual cues to maintain runway heading and execute a safe takeoff.
Intercooler A device used to reduce the temperatures of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting
International Civil Aviation Organization (ICAO) The United Nations agency for developing the principles and techniques of international air navigation, and fostering planning and development of international civil air transport.
International standard atmosphere (IAS) A model of standard variation of pressure and temperature.
Interpolation The estimation of an intermediate value of a quantity that falls between marked values in a series. Example: In a measurement of length, with a rule that is marked in eighths of an inch, the value falls between 3/8 inch and 1/2 inch. The estimated (interpolated) value might then be said to be 7/16 inch
Inversion An increase in temperature with altitude.
Inversion illusion The feeling that the aircraft is tumbling backwards, caused by an abrupt change from climb to straight- and-level flight while in situations lacking visual reference.
Inverter A solid-state electronic device that converts D.C. into A.C. current of the proper voltage and frequency to operate A.C. gyro instruments
Isobars Lines which connect points of equal barometric pressure.
IVSI See instantaneous vertical speed indicator.
Jet route A route designated to serve flight operations from 18,000 feet MSL up to and including FL 450.
Jet stream A high-velocity narrow stream of winds, usually found near the upper limit of the troposphere, which flows generally from west to east.
Judgment The mental process of recognizing and analyzing all pertinent information in a particular situation, a rational evaluation of alternative actions in response to it, and a timely decision on which action to take.
KIAS Knots indicated airspeed.
Kollsman window A barometric scale window of a sensitive altimeter used to adjust the altitude for the altimeter setting.
LAAS See local area augmentation system.
Lag The delay that occurs before an instrument needle attains a stable indication.
Land breeze A coastal breeze flowing from land to sea caused by temperature differences when the sea surface is warmer than the adjacent land. The land breeze usually occurs at night and alternates with the sea breeze that blows in the opposite direction by day
Land as soon as possible Land without delay at the nearest suitable area, such as an open field, at which a safe approach and landing is assured.
Land as soon as practical The landing site and duration of flight are at the discretion of the pilot. Extended flight beyond the nearest approved landing area is not recommended
Land immediately The urgency of the landing is paramount. The primary consideration is to ensure the survival of the occupants. Landing in trees, water, or other unsafe areas should be considered only as a last resort
Lateral axis An imaginary line passing through the center of gravity of an airplane and extending across the airplane from wingtip to wingtip.
Lateral stability (rolling) The stability about the longitudinal axis of an aircraft. Rolling stability or the ability of an airplane to return to level flight due to a disturbance that causes one of the wings to drop
Latitude Measurement north or south of the equator in degrees, minutes, and seconds. Lines of latitude are also referred to as parallels
LDA See localizer-type directional aid.
Lead radial The radial at which the turn from the DME arc to the inbound course is started.
Leading edge The part of an airfoil that meets the airflow first.
Leading edge devices High lift devices which are found on the leading edge of the airfoil. The most common types are fixed slots, movable slats, and leading edge flaps
Leading-edge flap A portion of the leading edge of an airplane wing that folds downward to increase the camber, lift, and drag of the wing. The leading-edge flaps are extended for takeoffs and landings to increase the amount of aerodynamic lift that is produced at any given airspeed
Leans, the A physical sensation caused by an abrupt correction of a banked attitude entered too slowly to stimulate the motion sensing system in the inner ear. The abrupt correction can create the illusion of banking in the opposite direction
Licensed empty weight The empty weight that consists of the airframe, engine(s), unusable fuel, and undrainable oil plus standard and optional equipment as specified in the equipment list. Some manufacturers used this term prior to GAMA standardization
Lift A component of the total aerodynamic force on an airfoil and acts perpendicular to the relative wind.
Limit load factor Amount of stress, or load factor, that an aircraft can withstand before structural damage or failure occurs.
Lines of flux Invisible lines of magnetic force passing between the poles of a magnet.
L/MF See low or medium frequency.
LMM See locator middle marker.
Load factor The ratio of a specified load to the total weight of the aircraft. The specified load is expressed in terms of any of the following: aerodynamic forces, inertial forces, or ground or water reactions
LOC See localizer.
Local area augmentation system (LAAS) A differential global positioning system (DGPS) that improves the accuracy of the system by determining position error from the GPS satellites, then transmitting the error, or corrective factors, to the airborne GPS receiver.
Localizer (LOC) The portion of an ILS that gives left/right guidance information down the centerline of the instrument runway for final approach.
Localizer-type directional aid (LDA) A NAVAID used for nonprecision instrument approaches with utility and accuracy comparable to a localizer but which is not a part of a complete ILS and is not aligned with the runway. Some LDAs are equipped with a glideslope
Locator middle marker (LMM) Nondirectional radio beacon (NDB) compass locator, collocated with a middle marker (MM).
Locator outer marker (LOM) NDB compass locator, collocated with an outer marker (OM).
LOM See locator outer marker.
Longitude Measurement east or west of the Prime Meridian in degrees, minutes, and seconds. The Prime Meridian is 0° longitude and runs through Greenwich, England. Lines of longitude are also referred to as meridians
Longitudinal axis An imaginary line through an aircraft from nose to tail, passing through its center of gravity. The longitudinal axis is also called the roll axis of the aircraft. Movement of the ailerons rotates an airplane about its longitudinal axis
Longitudinal stability (pitching) Stability about the lateral axis. A desirable characteristic of an airplane whereby it tends to return to its trimmed angle of attack after displacement
Long range navigation (LORAN) An electronic navigational system by which hyperbolic lines of position are determined by measuring the difference in the time of reception of synchronized pulse signals from two fixed transmitters. LORAN-A operates in the 1750–1950 kHz frequency band. LORAN-C and -D operate in the 100–110 kHz frequency band
LORAN See long range navigation.
Low or medium frequency A frequency range between 190 and 535 kHz with the medium frequency above 300 kHz. Generally associated with nondirectional beacons transmitting a continuous carrier with either a 400 or 1,020 Hz modulation
MAA See maximum authorized altitude.
MAC See mean aerodynamic chord.
Mach meter The instrument that displays the ratio of the speed of sound to the true airspeed an aircraft is flying.
Magnetic bearing (MB) The direction to or from a radio transmitting station measured relative to magnetic north.
Magnetic compass A device for determining direction measured from magnetic north.
Magnetic dip A vertical attraction between a compass needle and the magnetic poles. The closer the aircraft is to a pole, the more severe the effect
Magnetic heading (MH) The direction an aircraft is pointed with respect to magnetic north.
Magneto A self-contained, engine-driven unit that supplies electrical current to the spark plugs; completely independent of the airplane’s electrical system. Normally there are two magnetos per engine
Magnus effect Lifting force produced when a rotating cylinder produces a pressure differential. This is the same effect that makes a baseball curve or a golf ball slice
Mandatory altitude An altitude depicted on an instrument approach chart with the altitude value both underscored and overscored. Aircraft are required to maintain altitude at the depicted value
Mandatory block altitude An altitude depicted on an instrument approach chart with two underscored and overscored altitude values between which aircraft are required to maintain altitude.
Maneuverability Ability of an aircraft to change directions along a flightpath and withstand the stresses imposed upon it.
Maneuvering speed (VA) The maximum speed at which full, abrupt control movement can be used without overstressing the airframe.
Manifold absolute pressure The absolute pressure of the fuel/air mixture within the intake manifold, usually indicated in inches of mercury.
MAP See missed approach point.
Margin identification The top and bottom areas on an instrument approach chart that depict information about the procedure, including airport location and procedure identification.
Marker beacon A low-powered transmitter that directs its signal upward in a small, fan-shaped pattern. Used along the flight path when approaching an airport for landing, marker beacons indicate both aurally and visually when the aircraft is directly over the facility
Mass The amount of matter in a body.
Maximum altitude An altitude depicted on an instrument approach chart with overscored altitude value at which or below aircraft are required to maintain altitude.
Maximum authorized altitude (MAA) A published altitude representing the maximum usable altitude or flight level for an airspace structure or route segment.
Maximum landing weight The greatest weight that an airplane normally is allowed to have at landing.
Maximum ramp weight The total weight of a loaded aircraft, including all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and runup operations. Ramp weight may also be referred to as taxi weight
Maximum takeoff weight The maximum allowable weight for takeoff.
Maximum weight The maximum authorized weight of the aircraft and all of its equipment as specified in the Type Certificate Data Sheets (TCDS) for the aircraft.
Maximum zero fuel weight (GAMA) The maximum weight, exclusive of usable fuel.
MB See magnetic bearing.
MCA See minimum crossing altitude. MDA. See minimum descent altitude. MEA. See minimum en route altitude
Mean aerodynamic chord (MAC) The average distance from the leading edge to the trailing edge of the wing.
Mean sea level The average height of the surface of the sea at a particular location for all stages of the tide over a 19-year period.
MEL See minimum equipment list.
Meridians Lines of longitude.
Mesophere A layer of the atmosphere directly above the stratosphere.
METAR See Aviation Routine Weather Report.
MFD See Multi-function display.
MH See magnetic heading.
Microburts A strong downdraft which normally occurs over horizontal distances of 1 NM or less and vertical distances of less than 1,000 feet. In spite of its small horizontal scale, an intense microburst could induce windspeeds greater than 100 knots and downdrafts as strong as 6,000 feet per minute
Microwave landing system (MLS) A precision instrument approach system operating in the microwave spectrum which normally consists of an azimuth station, elevation station, and precision distance measuring equipment.
Mileage breakdown A fix indicating a course change that appears on the chart as an “x” at a break between two segments of a federal airway.
Military operations area (MOA) Airspace established for the purpose of separating certain military training activities from IFR traffic.
Military training route (MTR) Airspace of defined vertical and lateral dimensions established for the conduct of military training at airspeeds in excess of 250 knots indicated airspeed (KIAS).
Minimum altitude An altitude depicted on an instrument approach chart with the altitude value underscored. Aircraft are required to maintain altitude at or above the depicted value
Minimum crossing altitude (MCA) The lowest allowed altitude at certain fixes an aircraft must cross when proceeding in the direction of a higher minimum en route altitude (MEA).
Minimum descent altitude (MDA) The lowest altitude (in feet MSL) to which descent is authorized on final approach, or during circle-to-land maneuvering in execution of a nonprecision approach.
Minimum drag The point on the total drag curve where the lift-to-drag ratio is the greatest. At this speed, total drag is minimized
Minimum en route altitude (MEA) The lowest published altitude between radio fixes that ensures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes.
Minimum equipment list (MEL) A list developed for larger aircraft that outlines equipment that can be inoperative for various types of flight including IFR and icing conditions. This list is based on the master minimum equipment list (MMEL) developed by the FAA and must be approved by the FAA for use. It is specific to an individual aircraft make and model
Minimum obstruction clearance altitude (MOCA) The lowest published altitude in effect between radio fixes on VOR airways, off-airway routes, or route segments, which meets obstacle clearance requirements for the entire route segment and which ensures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR.
Minimum reception altitude (MRA) The lowest altitude at which an airway intersection can be determined.
Minimum safe altitude (MSA) The minimum altitude depicted on approach charts which provides at least 1,000 feet of obstacle clearance for emergency use within a specified distance from the listed navigation facility.
Minimum vectoring altitude (MVA) An IFR altitude lower than the minimum en route altitude (MEA) that provides terrain and obstacle clearance.
Minimums section The area on an IAP chart that displays the lowest altitude and visibility requirements for the approach.
Missed approach A maneuver conducted by a pilot when an instrument approach cannot be completed to a landing.
Missed approach point (MAP) A point prescribed in each instrument approach at which a missed approach procedure shall be executed if the required visual reference has not been established.
Mixed ice A mixture of clear ice and rime ice.
MLS See microwave landing system.
MM Middle marker.
MOA See military operations area.
MOCA See minimum obstruction clearance altitude.
Mode C Altitude reporting transponder mode.
Moment arm The distance from a datum to the applied force.
Moment index (or index) A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of airplanes where heavy items and long arms result in large, unmanageable numbers
Monocoque A shell-like fuselage design in which the stressed outer skin is used to support the majority of imposed stresses. Monocoque fuselage design may include bulkheads but not stringers
Monoplanes Airplanes with a single set of wings.
Movable slat A movable auxiliary airfoil on the leading edge of a wing. It is closed in normal flight but extends at high angles of attack. This allows air to continue flowing over the top of the wing and delays airflow separation
MRA See minimum reception altitude.
MSA See minimum safe altitude.
MSL See Mean sea level.
MTR See military training route.
Multi-function display (MFD) Small screen (CRT or LCD) in an aircraft that can be used to display information to the pilot in numerous configurable ways. Often an MFD will be used in concert with a primary flight display
MVA See minimum vectoring altitude.
N1 Rotational speed of the low pressure compressor in a turbine engine.
N2 Rotational speed of the high pressure compressor in a turbine engine.
Nacelle A streamlined enclosure on an aircraft in which an engine is mounted. On multiengine propeller-driven airplanes, the nacelle is normally mounted on the leading edge of the wing
NACG See National Aeronautical Charting Group.
NAS See National Airspace System.
National Airspace System (NAS) The common network of United States airspace—air navigation facilities, equipment and services, airports or landing areas; aeronautical charts, information and services; rules, regulations and procedures, technical information; and manpower and material.
National Aeronautical Charting Group (NACG) A Federal agency operating under the FAA, responsible for publishing charts such as the terminal procedures and en route charts.
National Route Program (NRP) A set of rules and procedures designed to increase the flexibility of user flight planning within published guidelines.
National Security Area (NSA) Areas consisting of airspace of defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities. Pilots are requested to voluntarily avoid flying through the depicted NSA. When it is necessary to provide a greater level of security and safety, flight in NSAs may be temporarily prohibited. Regulatory prohibitions are disseminated via NOTAMs
Transportation Safety Board (TSB) The TSB is an independent agency, created by an Act of Parliament that came into force on 29 March 1990. The Canadian Transportation Accident Investigation and Safety Board Act provides the legal framework that governs TSB activities. Their mandate is to advance transportation safety in the marine, pipeline, rail and air modes of transportation by conducting independent investigations, including public inquiries when necessary, into selected transportation occurrences in order to make findings as to their causes and contributing factors, identifying safety deficiencies, as evidenced by transportation occurrences, making recommendations designed to eliminate or reduce any such safety deficiencies and reporting publicly on our investigations and on the findings in relation thereto. As part of its ongoing investigations, the TSB also reviews developments in transportation safety and identifies safety risks that it believes government and the transportation industry should address to reduce injury and loss.
NAVAID Naviagtional aid.
NAV/COM Navigation and communication radio.
NDB See Nondirectional radio beacon.
Negative static stability The initial tendency of an aircraft to continue away from the original state of equilibrium after being disturbed.
Neutral static stability The initial tendency of an aircraft to remain in a new condition after its equilibrium has been disturbed.
NM Nautical mile.
NOAA National Oceanic and Atmospheric Administration.
No-gyro approach A radar approach that may be used in case of a malfunctioning gyro-compass or directional gyro. Instead of providing the pilot with headings to be flown, the controller observes the radar track and issues control instructions “turn right/left” or “stop turn,” as appropriate
Nondirectional radio beacon (NDB) A ground-based radio transmitter that transmits radio energy in all directions.
Nonprecision approach A standard instrument approach procedure in which only horizontal guidance is provided.
No procedure turn (NoPT) Term used with the appropriate course and altitude to denote that the procedure turn is not required.
NoPT See no procedure turn.
NOTAM See Notice to Airmen.
Notice to Airmen (NOTAM) A notice filed with an aviation authority to alert aircraft pilots of any hazards en route or at a specific location. The authority in turn provides means of disseminating relevant NOTAMs to pilots
NRP See National Route Program.
NSA See National Security Area.
TSB See Transportation Safety Board.
NWS National Weather Service.
Obstacle departure procedures (ODP) A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC
Obstruction lights Lights that can be found both on and off an airport to identify obstructions.
Occluded front A frontal occlusion occurs when a fast- moving cold front catches up with a slow moving warm front. The difference in temperature within each frontal system is a major factor in determining whether a cold or warm front occlusion occurs
ODP See obstacle departure procedures.
OM Outer marker.
Omission error The failure to anticipate significant instrument indications following attitude changes; for example, concentrating on pitch control while forgetting about heading or roll information, resulting in erratic control of heading and bank.
Optical illusion A misleading visual image. For the purpose of this handbook, the term refers to the brain’s misinterpretation of features on the ground associated with landing, which causes a pilot to misread the spatial relationships between the aircraft and the runway
Orientation Awareness of the position of the aircraft and of oneself in relation to a specific reference point.
Otolith organ An inner ear organ that detects linear acceleration and gravity orientation.
Outer marker A marker beacon at or near the glideslope intercept altitude of an ILS approach. It is normally located four to seven miles from the runway threshold on the extended centerline of the runway
Outside air temperature (OAT) The measured or indicated air temperature (IAT) corrected for compression and friction heating. Also referred to as true air temperature
Overcontrolling Using more movement in the control column than is necessary to achieve the desired pitch-and- bank condition.
Overboost A condition in which a reciprocating engine has exceeded the maximum manifold pressure allowed by the manufacturer. Can cause damage to engine components
Overpower To use more power than required for the purpose of achieving a faster rate of airspeed change.
P-static See precipitation static.
PAPI See precision approach path indicator.
PAR See precision approach radar.
Parallels Lines of latitude.
Parasite drag Drag caused by the friction of air moving over the aircraft structure; its amount varies directly with the airspeed.
Payload (GAMA) The weight of occupants, cargo, and baggage.
Personality The embodiment of personal traits and characteristics of an individual that are set at a very early age and extremely resistant to change.
P-factor A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft’s longitudinal axis is in a climbing attitude in relation to the relative wind. The P-factor would be to the right if the aircraft had a counterclockwise rotating propeller
PFD See primary flight display.
Phugoid oscillations Long-period oscillations of an aircraft around its lateral axis. It is a slow change in pitch accompanied by equally slow changes in airspeed. Angle of attack remains constant, and the pilot often corrects for phugoid oscillations without even being aware of them
PIC See pilot in command.
Pilotage Navigation by visual reference to landmarks.
Pilot in command (PIC) The pilot responsible for the operation and safety of an aircraft.
Pilot report (PIREP) Report of meteorological phenomena encountered by aircraft.
Pilot’s Operating Handbook/Airplane Flight Manual (POH/AFM) FAA-approved documents published by the airframe manufacturer that list the operating conditions for a particular model of aircraft.
PIREP See pilot report.
Pitot-static head A combination pickup used to sample pitot pressure and static air pressure.
Plan view The overhead view of an approach procedure on an instrument approach chart. The plan view depicts the routes that guide the pilot from the en route segments to the IAF
Planform The shape or form of a wing as viewed from above. It may be long and tapered, short and rectangular, or various other shapes
Pneumatic Operation by the use of compressed air.
POH/AFM See Pilot’s Operating Handbook/Airplane Flight Manual.
Point-in-space approach A type of helicopter instrument approach procedure to a missed approach point more than 2,600 feet from an associated helicopter landing area.
Poor judgment chain A series of mistakes that may lead to an accident or incident. Two basic principles generally associated with the creation of a poor judgment chain are: One bad decision often leads to another; and (2) as a string of bad decisions grows, it reduces the number of subsequent alternatives for continued safe flight. ADM is intended to break the poor judgment chain before it can cause an accident or incident.
Position error Error in the indication of the altimeter, ASI, and VSI caused by the air at the static system entrance not being absolutely still.
Position report A report over a known location as transmitted by an aircraft to ATC.
Positive static stability The initial tendency to return to a state of equilibrium when disturbed from that state.
Powerplant A complete engine and propeller combination with accessories.
Precession The characteristic of a gyroscope that causes an applied force to be felt, not at the point of application, but 90° from that point in the direction of rotation.
Precipitation Any or all forms of water particles (rain, sleet, hail, or snow) that fall from the atmosphere and reach the surface.
Precipitation static (P-static) A form of radio interference caused by rain, snow, or dust particles hitting the antenna and inducing a small radio-frequency voltage into it.
Precision approach A standard instrument approach procedure in which both vertical and horizontal guidance is provided.
Precision approach path indicator (PAPI) A system of lights similar to the VASI, but consisting of one row of lights in two- or four-light systems. A pilot on the correct glideslope will see two white lights and two red lights. See VASI
Precision approach radar (PAR) A type of radar used at an airport to guide an aircraft through the final stages of landing, providing horizontal and vertical guidance. The radar operator directs the pilot to change heading or adjust the descent rate to keep the aircraft on a path that allows it to touch down at the correct spot on the runway
Precision runway monitor (PRM) System allows simultaneous, independent instrument flight rules (IFR) approaches at airports with closely spaced parallel runways.
Preferred IFR routes Routes established in the major terminal and en route environments to increase system efficiency and capacity. IFR clearances are issued based on these routes, listed in the A/FD except when severe weather avoidance procedures or other factors dictate otherwise
Preignition Ignition occurring in the cylinder before the time of normal ignition. Preignition is often caused by a local hot spot in the combustion chamber igniting the fuel- air mixture
Pressure demand oxygen system A demand oxygen system that supplies 100 percent oxygen at sufficient pressure above the altitude where normal breathing is adequate. Also referred to as a pressure breathing system
Prevailing visibility The greatest horizontal visibility equaled or exceeded throughout at least half the horizon circle (which is not necessarily continuous).
Preventive maintenance Simple or minor preservative operations and the replacement of small standard parts not involving complex assembly operation as listed in 14 CFR part 43, appendix A. Certificated pilots may perform preventive maintenance on any aircraft that is owned or operated by them provided that the aircraft is not used in air carrier service
Primary and supporting A method of attitude instrument flying using the instrument that provides the most direct indication of attitude and performance.
Primary flight display (PFD) A display that provides increased situational awareness to the pilot by replacing the traditional six instruments used for instrument flight with an easy-to-scan display that provides the horizon, airspeed, altitude, vertical speed, trend, trim, and rate of turn among other key relevant indications.
PRM See precision runway monitor.
Procedure turn A maneuver prescribed when it is necessary to reverse direction to establish an aircraft on the intermediate approach segment or final approach course.
Profile view Side view of an IAP chart illustrating the vertical approach path altitudes, headings, distances, and fixes.
Prohibited area Designated airspace within which flight of aircraft is prohibited.
Propeller A device for propelling an aircraft that, when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane of rotation. It includes the control components normally supplied by its manufacturer
Propeller/rotor modulation error Certain propeller rpm settings or helicopter rotor speeds can cause the VOR course deviation indicator (CDI) to fluctuate as much as ± 6°. Slight changes to the rpm setting will normally smooth out this roughness.
Rabbit, the High-intensity flasher system installed at many large airports. The flashers consist of a series of brilliant blue-white bursts of light flashing in sequence along the approach lights, giving the effect of a ball of light traveling toward the runway
Radar A system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for Radio Detection and Ranging. The term has since entered the English language as a standard word, radar, losing the capitalization in the process
Radar approach The controller provides vectors while monitoring the progress of the flight with radar, guiding the pilot through the descent to the airport/heliport or to a specific runway.
Radar services Radar is a method whereby radio waves are transmitted into the air and are then received when they have been reflected by an object in the path of the beam. Range is determined by measuring the time it takes (at the speed of light) for the radio wave to go out to the object and then return to the receiving antenna. The direction of a detected object from a radar site is determined by the position of the rotating antenna when the reflected portion of the radio wave is received
Radar summary chart A weather product derived from the national radar network that graphically displays a summary of radar weather reports.
Radar weather report (SD) A report issued by radar stations at 35 minutes after the hour, and special reports as needed. Provides information on the type, intensity, and location of the echo tops of the precipitation
Radials The courses oriented from a station.
Radio or radar altimeter An electronic altimeter that determines the height of an aircraft above the terrain by measuring the time needed for a pulse of radio-frequency energy to travel from the aircraft to the ground and return.
Radio frequency (RF) A term that refers to alternating current (AC) having characteristics such that, if the current is input to antenna, an electromagnetic (EM) field is generated suitable for wireless broadcasting and/or communications.
Radio magnetic indicator (RMI) An electronic navigation instrument that combines a magnetic compass with an ADF or VOR. The card of the RMI acts as a gyro-stabilized magnetic compass, and shows the magnetic heading the aircraft is flying
Radiosonde A weather instrument that observes and reports meteorological conditions from the upper atmosphere. This instrument is typically carried into the atmosphere by some form of weather balloon
Radio wave An electromagnetic (EM) wave with frequency characteristics useful for radio transmission.
RAIM See receiver autonomous integrity monitoring.
RAM recovery The increase in thrust as a result of ram air pressures and density on the front of the engine caused by air velocity.
Random RNAV routes Direct routes, based on area navigation capability, between waypoints defined in terms of latitude/longitude coordinates, degree-distance fixes, or offsets from established routes/airways at a specified distance and direction.
Ranging signals Transmitted from the GPS satellite, signals allowing the aircraft’s receiver to determine range (distance) from each satellite.
Rapid decompression The almost instantaneous loss of cabin pressure in aircraft with a pressurized cockpit or cabin.
RB See relative bearing.
RBI See relative bearing indicator.
RCO See remote communications outlet.
Receiver autonomous integrity monitoring (RAIM) A system used to verify the usability of the received GPS signals and warns the pilot of any malfunction in the navigation system. This system is required for IFR-certified GPS units
Recommended altitude An altitude depicted on an instrument approach chart with the altitude value neither underscored nor overscored. The depicted value is an advisory value
Receiver-transmitter (RT) A system that receives and transmits a signal and an indicator.
Reduced vertical separation minimum (RVSM) Reduces the vertical separation between flight levels (FL) 290 and 410 from 2,000 feet to 1,000 feet, and makes six additional FLs available for operation. Also see DRVSM
Reference circle (also, distance circle) The circle depicted in the plan view of an IAP chart that typically has a 10 NM radius, within which chart the elements are drawn to scale.
Regions of command The “regions of normal and reversed command” refers to the relationship between speed and the power required to maintain or change that speed in flight.
Region of reverse command Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting in order to maintain altitude.
REIL See runway end identifier lights.
Relative bearing (RB) The angular difference between the aircraft heading and the direction to the station, measured clockwise from the nose of the aircraft.
Relative bearing indicator (RBI) Also known as the fixed- card ADF, zero is always indicated at the top of the instrument and the needle indicates the relative bearing to the station.
Relative humidity The ratio of the existing amount of water vapor in the air at a given temperature to the maximum amount that could exist at that temperature; usually expressed in percent.
Relative wind Direction of the airflow produced by an object moving through the air. The relative wind for an airplane in flight flows in a direction parallel with and opposite to the direction of flight; therefore, the actual flight path of the airplane determines the direction of the relative wind
Remote communications outlet (RCO) An unmanned communications facility that is remotely controlled by air traffic personnel.
Required navigation performance (RNP) A specified level of accuracy defined by a lateral area of confined airspace in which an RNP-certified aircraft operates.
Restricted area Airspace designated under 14 CFR part 73 within which the flight of aircraft, while not wholly prohibited, is subject to restriction.
Reverse sensing The VOR needle appearing to indicate the reverse of normal operation.
RF Radio frequency.
Rhodopsin The photosensitive pigments that initiate the visual response in the rods of the eye.
Rigging The final adjustment and alignment of an aircraft and its flight control system that provides the proper aerodynamic characteristics.
Rigidity The characteristic of a gyroscope that prevents its axis of rotation tilting as the Earth rotates.
Risk The future impact of a hazard that is not eliminated or controlled.
Risk elements There are four fundamental risk elements in aviation: the pilot, the aircraft, the environment, and the type of operation that comprise any given aviation situation.
Risk management The part of the decision-making process which relies on situational awareness, problem recognition, and good judgment to reduce risks associated with each flight.
RMI See Radio magnetic indicator.
RNAV See area navigation.
RNP See required navigation performance.
RT See receiver-transmitter.
Rudder The movable primary control surface mounted on the trailing edge of the vertical fin of an airplane. Movement of the rudder rotates the airplane about its vertical axis
Runway centerline lights Runway lighting which consists of flush centerline lights spaced at 50-foot intervals beginning 75 feet from the landing threshold.
Runway edge lights A component of the runway lighting system that is used to outline the edges of runways at night or during low visibility conditions. These lights are classified according to the intensity they are capable of producing
Runway end identifier lights (REIL) A pair of synchronized flashing lights, located laterally on each side of the runway threshold, providing rapid and positive identification of the approach end of a runway.
Runway visibility value (RVV) The visibility determined for a particular runway by a transmissometer.
Runway visual range (RVR) The instrumentally derived horizontal distance a pilot should be able to see down the runway from the approach end, based on either the sighting of high-intensity runway lights, or the visual contrast of other objects.
RVR See runway visual range. RVV. See runway visibility value. SA. See selective availability
St Elmo’s Fire. A corona discharge which lights up the aircraft surface areas where maximum static discharge occurs
Satellite ephemeris data Data broadcast by the GPS satellite containing very accurate orbital data for that satellite, atmospheric propagation data, and satellite clock error data.
Sea breeze A coastal breeze blowing from sea to land caused by the temperature difference when the land surface is warmer than the sea surface. The sea breeze usually occurs during the day and alternates with the land breeze that blows in the opposite direction at night
Sea level engine A reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.
Scan The first fundamental skill of instrument flight, also known as “cross-check;” the continuous and logical observation of instruments for attitude and performance information.
Sectional aeronautical charts Designed for visual navigation of slow- or medium-speed aircraft. Topographic information on these charts features the portrayal of relief, and a judicious selection of visual check points for VFR flight. Aeronautical information includes visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions and related data
SDF See simplified directional facility.
Selective availability (SA) A satellite technology permitting the Department of Defense (DOD) to create, in the interest of national security, a significant clock and ephemeris error in the satellites, resulting in a navigation error.
Semicircular canal An inner ear organ that detects angular acceleration of the body.
Sensitive altimeter A form of multipointer pneumatic altimeter with an adjustable barometric scale that allows the reference pressure to be set to any desired level.
Service ceiling The maximum density altitude where the best rate-of-climb airspeed will produce a 100-feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.
SIDS See standard instrument departure procedures.
SIGMET The acronym for Significant Meteorological information. A weather advisory issued concerning weather significant to the safety of all aircraft
Signal-to-noise ratio An indication of signal strength received compared to background noise, which is a measure of the adequacy of the received signal.
Significant weather prognostic Presents four panels showing forecast significant weather.
Simplex Transmission and reception on the same frequency.
Simplified directional facility (SDF) A NAVAID used for nonprecision instrument approaches. The final approach course is similar to that of an ILS localizer; however, the SDF course may be offset from the runway, generally not more than 3°, and the course may be wider than the localizer, resulting in a lower degree of accuracy
Single-pilot resource management (SRM) The ability for a pilot to manage all resources effectively to ensure the outcome of the flight is successful.
Situational awareness Pilot knowledge of where the aircraft is in regard to location, air traffic control, weather, regulations, aircraft status, and other factors that may affect flight.
Skidding turn An uncoordinated turn in which the rate of turn is too great for the angle of bank, pulling the aircraft to the outside of the turn.
Skills and procedures The procedural, psychomotor, and perceptual skills used to control a specific aircraft or its systems. They are the airmanship abilities that are gained through conventional training, are perfected, and become almost automatic through experience
Skin friction drag Drag generated between air molecules and the solid surface of the aircraft.
Slant range The horizontal distance from the aircraft antenna to the ground station, due to line-of-sight transmission of the DME signal.
Slaved compass A system whereby the heading gyro is “slaved to,” or continuously corrected to bring its direction readings into agreement with a remotely located magnetic direction sensing device (usually a flux valve or flux gate compass).
Slipping turn An uncoordinated turn in which the aircraft is banked too much for the rate of turn, so the horizontal lift component is greater than the centrifugal force, pulling the aircraft toward the inside of the turn.
Small airplane An airplane of 12,500 pounds or less maximum certificated takeoff weight.
Somatogravic illusion The misperception of being in a nose-up or nose-down attitude, caused by a rapid acceleration or deceleration while in flight situations that lack visual reference.
Spatial disorientation The state of confusion due to misleading information being sent to the brain from various sensory organs, resulting in a lack of awareness of the aircraft position in relation to a specific reference point.
Special flight permit A flight permit issued to an aircraft that does not meet airworthiness requirements but is capable of safe flight. A special flight permit can be issued to move an aircraft for the purposes of maintenance or repair, buyer delivery, manufacturer flight tests, evacuation from danger, or customer demonstration. Also referred to as a ferry permit
Special use airspace Airspace in which flight activities are subject to restrictions that can create limitations on the mixed use of airspace. Consists of prohibited, restricted, warning, military operations, and alert areas
Special fuel consumption The amount of fuel in pounds per hour consumed or required by an engine per brake horsepower or per pound of thrust.
Speed The distance traveled in a given time.
Spiral instability A condition that exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.
Spiraling slipstream The slipstream of a propeller-driven airplane rotates around the airplane. This slipstream strikes the left side of the vertical fin, causing the aircraft to yaw slightly. Rudder offset is sometimes used by aircraft designers to counteract this tendency
SRM See single-pilot resource management.
SSR See secondary surveillance radar.
SSV See standard service volume.
Stability The inherent quality of an airplane to correct for conditions that may disturb its equilibrium, and to return or to continue on the original flightpath. It is primarily an airplane design characteristic
Stagnant hypoxia A type of hypoxia that results when the oxygen-rich blood in the lungs is not moving to the tissues that need it.
Stall A rapid decrease in lift caused by the separation of airflow from the wing’s surface, brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed
Standard atmosphere At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury ("Hg) or 1013.2 millibars, and a temperature of 15 °C (59 °F). Pressure and temperature normally decrease as altitude increases. The standard lapse rate in the lower atmosphere for each 1,000 feet of altitude is approximately 1 "Hg and 2 °C (3.5 °F). For example, the standard pressure and temperature at 3,000 feet mean sea level (MSL) are 26.92 "Hg (29.92 "Hg – 3 "Hg) and 9 °C (15 °C – 6 °C).
Standard empty weight (GAMA) This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.
Standard holding pattern A holding pattern in which all turns are made to the right.
Standard instrument departure procedures (SIDS) Published procedures to expedite clearance delivery and to facilitate transition between takeoff and en route operations.
Standard rate turn A turn in which an aircraft changes its direction at a rate of 3° per second (360° in 2 minutes) for low- or medium-speed aircraft. For high-speed aircraft, the standard rate turn is 1½° per second (360° in 4 minutes)
Standard service volume (SSV) Defines the limits of the volume of airspace which the VOR serves.
Standard terminal arrival route (STAR) A preplanned IFR ATC arrival procedure published for pilot use in graphic and/or textual form.
Standard weights Weights established for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available
STAR See standard terminal arrival route.
Static longitudinal stability The aerodynamic pitching moments required to return the aircraft to the equilibrium angle of attack.
Static pressure Pressure of air that is still or not moving, measured perpendicular to the surface of the aircraft.
Static stability The initial tendency an aircraft displays when disturbed from a state of equilibrium.
Station A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches
Stationary front A front that is moving at a speed of less than 5 knots.
Steep turns In instrument flight, any turn greater than standard rate; in visual flight, anything greater than a 45° bank.
Stepdown fix The point after which additional descent is permitted within a segment of an IAP.
Strapdown system An INS in which the accelerometers and gyros are permanently “strapped down” or aligned with the three axes of the aircraft.
Stratoshere A layer of the atmosphere above the tropopause extending to a height of approximately 160,000 feet.
Stress management The personal analysis of the kinds of stress experienced while flying, the application of appropriate stress assessment tools, and other coping mechanisms.
Structural icing The accumulation of ice on the exterior of the aircraft.
Suction relief valve A relief valve in an instrument vacuum system required to maintain the correct low pressure inside the instrument case for the proper operation of the gyros.
Supercharger An engine- or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power.
Supercooled water droplets Water droplets that have been cooled below the freezing point, but are still in a liquid state.
Surface analysis chart A report that depicts an analysis of the current surface weather. Shows the areas of high and low pressure, fronts, temperatures, dewpoints, wind directions and speeds, local weather, and visual obstructions
Synchro A device used to transmit indications of angular movement or position from one location to another.
Synthetic vision A realistic display depiction of the aircraft in relation to terrain and flight path.
TAA See terminal arrival area.
TACAN See tactical air navigation.
Tactical air navigation (TACAN) An electronic navigation system used by military aircraft, providing both distance and direction information.
Takeoff decision speed (V1) Per 14 CFR section 23.51: “the calibrated airspeed on the ground at which, as a result of engine failure or other reasons, the pilot assumed to have made a decision to continue or discontinue the takeoff.”
Takeoff distance The distance required to complete an all-engines operative takeoff to the 35-foot height. It must be at least 15 percent less than the distance required for a one-engine inoperative engine takeoff. This distance is not normally a limiting factor as it is usually less than the one- engine inoperative takeoff distance
Takeoff safety speed (V2) Per 14 CFR part 1: “A referenced airspeed obtained after lift-off at which the required one- engine-inoperative climb performance can be achieved?”.
TAWS See terrain awareness and warning system.
Taxiway lights Omnidirectional lights that outline the edges of the taxiway and are blue in color.
Taxiway turnoff lights Lights that are flush with the runway which emit a steady green color.
TCAS See Traffic alert collision avoidance system.
TCH See threshold crossing height. TDZE. See touchdown zone elevation. TEC. See Tower En Route Control
Technique The manner in which procedures are executed.
Telephone information briefing service (TIBS) Telephone recording of area and/or route meteorological briefings, airspace procedures, and special aviation-oriented announcements.
Temporary flight restriction (TFR) Restriction to flight imposed in order to: (update).
Tension Maintaining an excessively strong grip on the control column, usually resulting in an overcontrolled situation.
Terminal aerodrome forecast (TAF) A report established for the 5 statute mile radius around an airport. Utilizes the same descriptors and abbreviations as the METAR report
Terminal arrival area (TAA) A procedure to provide a new transition method for arriving aircraft equipped with FMS and/or GPS navigational equipment. The TAA contains a “T” structure that normally provides a NoPT for aircraft using the approach
Terminal instrument approach procedure (TERP) Prescribes standardized methods for use in designing instrument flight procedures.
TERP See terminal instrument approach procedure.
Terminal radar service areas (TRSA) Areas where participating pilots can receive additional radar services. The purpose of the service is to provide separation between all IFR operations and participating VFR aircraft
Terrain awareness and warning system (TAWS) A timed-based system that provides information concerning potential hazards with fixed objects by using GPS positioning and a database of terrain and obstructions to provide true predictability of the upcoming terrain and obstacles.
TFR See temporary flight restriction.
Thermosphere The last layer of the atmosphere that begins above the mesosphere and gradually fades away into space.
Threshold crossing height (TCH) The theoretical height above the runway threshold at which the aircraft’s glideslope antenna would be if the aircraft maintained the trajectory established by the mean ILS glideslope or MLS glidepath.
Thrust The force which imparts a change in the velocity of a mass. This force is measured in pounds but has no element of time or rate. The term “thrust required” is generally associated with jet engines. A forward force which propels the airplane through the air
Thrust (aerodynamic force) The forward aerodynamic force produced by a propeller, fan, or turbojet engine as it forces a mass of air to the rear, behind the aircraft.
Thrust line An imaginary line passing through the center of the propeller hub, perpendicular to the plane of the propeller rotation.
Time and speed table A table depicted on an instrument approach procedure chart that identifies the distance from the FAF to the MAP, and provides the time required to transit that distance based on various groundspeeds.
Timed turn A turn in which the clock and the turn coordinator are used to change heading a definite number of degrees in a given time.
TIS See traffic information service.
Title 14 of the Code of Federal Regulations (14 CFR) Includes the federal aviation regulations governing the operation of aircraft, airways, and airmen.
Torque (1) A resistance to turning or twisting. (2) Forces that produce a twisting or rotating motion. (3) In an airplane, the tendency of the aircraft to turn (roll) in the opposite direction of rotation of the engine and propeller. (4) In helicopters with a single, main rotor system, the tendency of the helicopter to turn in the opposite direction of the main rotor rotation
Torquemeter An instrument used with some of the larger reciprocating engines and turboprop or turboshaft engines to measure the reaction between the propeller reduction gears and the engine case.
Total drag The sum of the parasite drag and induced drag.
Touchdown zone elevation (TDZE) The highest elevation in the first 3,000 feet of the landing surface, TDZE is indicated on the instrument approach procedure chart when straight-in landing minimums are authorized.
Touchdown zone lights Two rows of transverse light bars disposed symmetrically about the runway centerline in the runway touchdown zone.
Tower En Route Control (TEC) The control of IFR en route traffic within delegated airspace between two or more adjacent approach control facilities, designed to expedite traffic and reduce control and pilot communication requirements.
TPP See United States Terminal Procedures Publication.
Track The actual path made over the ground in flight.
Tracking Flying a heading that will maintain the desired track to or from the station regardless of crosswind conditions.
Traffic Alert Collision Avoidance System (TCAS) An airborne system developed by the FAA that operates independently from the ground-based Air Traffic Control system. Designed to increase flight deck awareness of proximate aircraft and to serve as a “last line of defense” for the prevention of midair collisions
Traffic information service (TIS) A ground-based service providing information to the flight deck via data link using the S-mode transponder and altitude encoder to improve the safety and efficiency of “see and avoid” flight through an automatic display that informs the pilot of nearby traffic.
Trailing edge The portion of the airfoil where the airflow over the upper surface rejoins the lower surface airflow.
Transcribed Weather Broadcast (TWEB) Meteorological and aeronautical data recorded on tapes and broadcast over selected NAVAIDs. Generally, the broadcast contains route- oriented data with specially prepared NWS forecasts, inflight advisories, and winds aloft. It also includes selected current information such as weather reports (METAR/SPECI), NOTAMs, and special notices
Transponder The airborne portion of the ATC radar beacon system.
Transponder code One of 4,096 four-digit discrete codes ATC assigns to distinguish between aircraft.
Trend Immediate indication of the direction of aircraft movement, as shown on instruments.
Tricycle gear Landing gear employing a third wheel located on the nose of the aircraft.
Trim To adjust the aerodynamic forces on the control surfaces so that the aircraft maintains the set attitude without any control input.
Tropopause The boundary layer between the troposphere and the mesosphere which acts as a lid to confine most of the water vapor, and the associated weather, to the troposphere.
Troposphere The layer of the atmosphere extending from the surface to a height of 20,000 to 60,000 feet, depending on latitude.
True altitude The vertical distance of the airplane above sea level—the actual altitude. It is often expressed as feet above mean sea level (MSL). Airport, terrain, and obstacle elevations on aeronautical charts are true altitudes
Truss A fuselage design made up of supporting structural members that resist deformation by applied loads. The truss- type fuselage is constructed of steel or aluminum tubing. Strength and rigidity is achieved by welding the tubing together into a series of triangular shapes, called trusses
T-tail An aircraft with the horizontal stabilizer mounted on the top of the vertical stabilizer, forming a T.
Turbine discharge pressure The total pressure at the discharge of the low-pressure turbine in a dual-turbine axial- flow engine.
Turbine engine An aircraft engine which consists of an air compressor, a combustion section, and a turbine. Thrust is produced by increasing the velocity of the air flowing through the engine
Turbocharger An air compressor driven by exhaust gases, which increases the pressure of the air going into the engine through the carburetor or fuel injection system.
Turbofan engine A fanlike turbojet engine designed to create additional thrust by diverting a secondary airflow around the combustion chamber.
Turbojet engine A turbine engine which produces its thrust entirely by accelerating the air through the engine.
Turboprop engine A turbine engine which drives a propeller through a reduction gearing arrangement. Most of the energy in the exhaust gases is converted into torque, rather than using its acceleration to drive the aircraft
Turboshaft engine A gas turbine engine that delivers power through a shaft to operate something other than a propeller.
Turn-and-slip indicator A flight instrument consisting of a rate gyro to indicate the rate of yaw and a curved glass inclinometer to indicate the relationship between gravity and centrifugal force. The turn-and-slip indicator indicates the relationship between angle of bank and rate of yaw. Also called a turn-and-bank indicator
Turn coordinator A rate gyro that senses both roll and yaw due to the gimbal being canted. Has largely replaced the turn-and-slip indicator in modern aircraft
TWEB See Transcribed Weather Broadcast.
UHF See Ultra-high frequency.
Ultra-high frequency (UHF) The range of electromagnetic frequencies between 962 MHz and 1213 MHz.
Ultimate load factor In stress analysis, the load that causes physical breakdown in an aircraft or aircraft component during a strength test, or the load that according to computations, should cause such a breakdown.
Uncaging Unlocking the gimbals of a gyroscopic instrument, making it susceptible to damage by abrupt flight maneuvers or rough handling.
Uncontrolled airspace Class G airspace that has not been designated as Class A, B, C, D, or E. It is airspace in which air traffic control has no authority or responsibility to control air traffic; however, pilots should remember there are VFR minimums which apply to this airspace
Underpower Using less power than required for the purpose of achieving a faster rate of airspeed change.
United States Terminal Procedures Publication (TPP) Booklets published in regional format by the NACO that include DPs, STARs, IAPs, and other information pertinent to IFR flight.
Unusual attitude An unintentional, unanticipated, or extreme aircraft attitude.
Useful load The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only
User-defined waypoints Waypoint location and other data which may be input by the user, this is the only GPS database information that may be altered (edited) by the user.
V1 See takeoff decision speed.
V2 See takeoff safety speed.
VA The design maneuvering speed. The maximum speed at which full, abrupt control movement can be used without overstressing the airframe
Vapor lock A problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporise due to being heated by the engine, by the local climate or due to a lower boiling point at high altitude
Variation Compass error caused by the difference in the physical locations of the magnetic north pole and the geographic North Pole.
VASI See visual approach slope indicator.
VDP See visual descent point.
Vector A force vector is a graphic representation of a force and shows both the magnitude and direction of the force.
Vectoring Navigational guidance by assigning headings.
Velocity The speed or rate of movement in a certain direction.
Venturi tube A specially shaped tube attached to the outside of an aircraft to produce suction to allow proper operation of gyro instruments.
Vertical axis An imaginary line passing vertically through the center of gravity of an aircraft. The vertical axis is called the z-axis or the yaw axis
Vertical card compass A magnetic compass that consists of an azimuth on a vertical card, resembling a heading indicator with a fixed miniature airplane to accurately present the heading of the aircraft. The design uses eddy current damping to minimize lead and lag during turns
Vertical speed indicator (VSI) A rate-of-pressure change instrument that gives an indication of any deviation from a constant pressure level.
Vertical stability Stability about an aircraft’s vertical axis. Also called yawing or directional stability
Very-high frequency (VHF) A band of radio frequencies falling between 30 and 300 MHz.
Very-high frequency omnidirectional range (VOR) Electronic navigation equipment in which the flight deck instrument identifies the radial or line from the VOR station, measured in degrees clockwise from magnetic north, along which the aircraft is located.
Vestibule The central cavity of the bony labyrinth of the ear, or the parts of the membranous labyrinth that it contains.
VFE The maximum speed with the flaps extended. The upper limit of the white arc
VFR See visual flight rules.
VFR on top ATC authorization for an IFR aircraft to operate in VFR conditions at any appropriate VFR altitude.
VFR over the top A VFR operation in which an aircraft operates in VFR conditions on top of an undercast.
VFR terminal area chart At a scale of 1:250,000, a chart that depicts Class B airspace, which provides for the control or segregation of all the aircraft within the Class B airspace. The chart depicts topographic information and aeronautical information including visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions, and related data
V-G diagram A chart that relates velocity to load factor. It is valid only for a specific weight, configuration and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed. Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds
Victor airways Airways based on a centerline that extends from one VOR or VORTAC navigation aid or intersection, to another navigation aid (or through several navigation aids or intersections); used to establish a known route for en route procedures between terminal areas.
Visual approach slope indicator (VASI) A visual aid of lights arranged to provide descent guidance information during the approach to the runway. A pilot on the correct glideslope will see red lights over white lights
Visual descent point (VDP) A defined point on the final approach course of a nonprecision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided the runway environment is clearly visible to the pilot.
Visual flight rules (VFR) Flight rules adopted by the FAA governing aircraft flight using visual references. VFR operations specify the amount of ceiling and the visibility the pilot must have in order to operate according to these rules. When the weather conditions are such that the pilot cannot operate according to VFR, he or she must use instrument flight rules (IFR)
Visual meteorological conditions (VMC) Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling meeting or exceeding the minimums specified for VFR.
VLE Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended
VLO Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear
VMC Minimum control airspeed. This is the minimum flight speed at which a light, twin-engine airplane can be satisfactorily controlled when an engine suddenly becomes inoperative and the remaining engine is at takeoff power
VMC See visual meteorological conditions.
VNE The never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure. The red line on the airspeed indicator
VNO The maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc
VOR See very-high frequency omnidirectional range.
VORTAC A facility consisting of two components, VOR and TACAN, which provides three individual services: VOR azimuth, TACAN azimuth, and TACAN distance (DME) at one site.
VOR test facility (VOT) A ground facility which emits a test signal to check VOR receiver accuracy. Some VOTs are available to the user while airborne, while others are limited to ground use only
VOT See VOR test facility.
VSI See vertical speed indicator.
VS0 The stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down). The lower limit of the white arc
VS1 The stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up). The lower limit of the green arc
V-tail A design which utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers
VX Best angle-of-climb speed. The airspeed at which an airplane gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle
VY Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time
VYSE Best rate-of-climb speed with one engine inoperative. This airspeed provides the most altitude gain in a given period of time in a light, twin-engine airplane following an engine failure
WAAS See wide area augmentation system.
Wake turbulence Wingtip vortices that are created when an airplane generates lift. When an airplane generates lift, air spills over the wingtips from the high pressure areas below the wings to the low pressure areas above them. This flow causes rapidly rotating whirlpools of air called wingtip vortices or wake turbulence
Warm front The boundary area formed when a warm air mass contacts and flows over a colder air mass. Warm fronts cause low ceilings and rain
Warning area An area containing hazards to any aircraft not participating in the activities being conducted in the area. Warning areas may contain intensive military training, gunnery exercises, or special weapons testing
WARP See weather and radar processing.
Waste gate A controllable valve in the tailpipe of an aircraft reciprocating engine equipped with a turbocharger. The valve is controlled to vary the amount of exhaust gases forced through the turbocharger turbine
Waypoint A designated geographical location used for route definition or progress-reporting purposes and is defined in terms of latitude/longitude coordinates.
WCA See wind correction angle.
Weather and radar processor (WARP) A device that provides real-time, accurate, predictive, and strategic weather information presented in an integrated manner in the National Airspace System (NAS).
Weather depiction chart Details surface conditions as derived from METAR and other surface observations.
Weight The force exerted by an aircraft from the pull of gravity.
Wide area augmentation system (WAAS) A differential global positioning system (DGPS) that improves the accuracy of the system by determining position error from the GPS satellites, then transmitting the error, or corrective factors, to the airborne GPS receiver.
Wind correction angle (WCA) The angle between the desired track and the heading of the aircraft necessary to keep the aircraft tracking over the desired track.
Wind direction indicators Indicators that include a wind sock, wind tee, or tetrahedron. Visual reference will determine wind direction and runway in use
Wind shear A sudden, drastic shift in windspeed, direction, or both that may occur in the horizontal or vertical plane.
Winds and temperature aloft forecast (FD) A twice daily forecast that provides wind and temperature forecasts for specific locations in the contiguous United States.
Wing area The total surface of the wing (in square feet), which includes control surfaces and may include wing area covered by the fuselage (main body of the airplane), and engine nacelles.
Wings Airfoils attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight.
Wing span The maximum distance from wingtip to wingtip.
Wingtip vortices The rapidly rotating air that spills over an airplane’s wings during flight. The intensity of the turbulence depends on the airplane’s weight, speed, and configuration. Also referred to as wake turbulence. Vortices from heavy aircraft may be extremely hazardous to small aircraft
Wing twist A design feature incorporated into some wings to improve aileron control effectiveness at high angles of attack during an approach to a stall.
World Aeronautical Charts (WAC) A standard series of aeronautical charts covering land areas of the world at a size and scale convenient for navigation (1:1,000,000) by moderate speed aircraft. Topographic information includes cities and towns, principal roads, railroads, distinctive landmarks, drainage, and relief. Aeronautical information includes visual and radio aids to navigation, airports, airways, restricted areas, obstructions and other pertinent data
Zone of confusion Volume of space above the station where a lack of adequate navigation signal directly above the VOR station causes the needle to deviate.
Zulu time A term used in aviation for coordinated universal time (UTC) which places the entire world on one time standard.
Course Deviation Indicator (CDI) A flight navigation instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a course. If the location of the aircraft is to the left of course, the needle deflects to the right, and vice versa.
ARTCC See Air route traffic control center.
ASDE See Airport surface detection equipment.
C of R See Certificate of Registration
Certificate of Registration (C of R) A certificate issued by Transport Canada to the individual or entity that has legal custody and control of an aircraft. This certificate details the custodian, the manufacturer, model & the serial number of the aircraft and the Nationality & Registration marks issued the aircraft.
C of A See Certificate of Airworthiness
TCCA See Transport Canada
Transport Canada (TCCA) The Civil Aviation Directorate, also known as Transport Canada Civil Aviation (TCCA), promotes the safety of the national air transportation system through its regulatory framework and oversight activities. They are responsible for advancing the safety of all aspects of civil aviation in Canada. (Civil aviation is distinguished from military aviation.) As part of the regulatory framework, they develop policies, guidelines, regulations, standards and educational materials to advance civil aviation safety in Canada. As part of our oversight activities, they verify that the aviation industry complies with the regulatory framework through certifications, assessments, validations, inspections and enforcement.
Canadian Aviation Regulations (CARS) Are the rules that govern civil aviation in Canada. The CARs became law on October 10, 1996 replacing the former Air Regulations and Air Navigation Orders. The authority for the establishment of the CARs is the Aeronautics Act. Both the Act and the CARs are the responsibility of the Minister of Transport and her department, Transport Canada. The CARs consist of regulations, standards and advisory material. Compliance with the regulations and standards is mandatory, while complying with the advisory material is not mandatory. Standards tell how to comply with the corresponding regulation.