Aviation Maintenance Terms beginning with A
Aborted takeoff
A takeoff that is terminated prematurely when it is determined that some condition exists that makes takeoff or further flight dangerous.
Abradable strip
A strip of material in the compressor housing of some axial-flow gas turbine engines. The tip of the compressor blade touches the abradable strip, and wears, or abrades a groove in it. This groove ensures the minimum tip clearance.
Abradable tip (compressor blade tip)
The tip of some axial-flow compressor blades constructed so that it will abrade, or wear away, upon contact with the compressor housing, which ensures the minimum tip clearance between the blade and the housing.
Abrasion resistant PTFE
A solid insulation wall of PTFE with hard, nonconductive grit positioned midway in the wall thickness, and significantly improves the resistance of the PTFE material to damage from wear.
Absolute humidity
The actual amount of the water vapor in a mixture of air and water.
Absolute pressure
Equal to gauge pressure plus atmospheric pressure.Also known as psia.
Absolute pressure
Pressure referenced from zero pressure or a vacuum.
Absolute pressure
Pressure measured from zero pressure or a vacuum.
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 temperature
Temperature measured relative to absolute zero. Absolute temperature scales include Kelvin and Rankine.
Absolute zero
The point at which all molecular motion ceases. Absolute zero is –460 °F and –273 °C.
Acceleration
The amount the velocity of an object is increased by a force during each second it is acted upon by that force. Acceleration is usually measured and expressed in terms of feet per second, per second (fps²).
Acceleration due to gravity
The acceleration of an object caused by gravity. On earth, it is measured as 32.2 feet per second per second (32.2 fps/s).
Accessory end
The end of a reciprocating engine on which many of the accessories are mounted. Also, called the anti- propeller end.
Accumulator
A hydraulic component that stores a non-compressible fluid, such as oil, under pressure. An accumulator has two compartments separated by a flexible or movable partition with one compartment containing compressed air. When oil is pumped into the other compartment, the partition moves over, further compressing the air which holds pressure on the oil.
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.
Acetylene
Gas composed of two parts of carbon and two parts of hydrogen. When burned in the atmosphere of oxygen, it produces one of the highest flame temperatures obtainable.
Acetylene regulator
Manually adjustable device used to reduce cylinder pressure to torch pressure and to keep the pressure constant. They are never to be used as oxygen regulators.
Actuator
A fluid power device that changes fluid pressure into mechanical motion.
Addition
The process in which the value of one number is added to the value of another.
Adherend
One of the members being bonded together by adhesive.
Adiabatic change
A physical change that takes place within a material in which heat energy is neither added to the material, nor taken away. If a container of gas is compressed, with no heat energy added to or taken from it, the gas will become hotter; its temperature will rise.
Administrator
The Federal Aviation Administrator or any person to whom he has delegated his authority in the matter concerned.
ADS-B Traffic Advisory System (ATAS)
An ADS-B In application that augments flight crew traffic situation awareness in support of the see-and-avoid responsibility by providing alerts of traffic that are detected in conflict with ownship. This application is named Traffic Situation Awareness with Alerts (TSAA) in RTCA DO-317B.
Advancing blade
The blade on a helicopter rotor whose tip is moving in the same direction the helicopter is moving.
Adverse yaw
A condition of flight at the beginning of a turn in which the nose of an airplane momentarily yaws in the opposite direction from the direction in which the turn is to be made.
Advisory
The level or category of alert for conditions that require flight crew awareness and may require subsequent flight crew response.
Advisory Circulars (AC)
Issued to inform the aviation public in a systematic way of nonregulatory material. An AC is issued to provide guidance and information in a designated subject area or to show a method acceptable to the Administrator for complying with a related 14 CFR part.
Aerodynamic coefficients
Non-dimensional coefficients for aerodynamic forces and moments.
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.
Aeromatic propeller
A patented variable-pitch propeller that has flyweights around the blade shanks and the blades angled back from the hub to increase the effects of aerodynamic and centrifugal twisting forces. This propeller automatically maintains a relatively constant rpm for any throttle setting.
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.
Aft-fan engine
A turbofan engine with the fan mounted behind the compressor section. The blades of an aft-fan are normally extensions of the free turbine blades.
Afterburner
A component in the exhaust system of a turbojet or turbofan engine used to increase the thrust for takeoff and for special flight conditions. Since much of the air passing through a gas turbine engine is used only for cooling, it still contains a great deal of oxygen. Fuel is sprayed into the hot, oxygen-rich exhaust in the afterburner, where it is ignited and burned to produce additional thrust.
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.
Agonic line
A line drawn on an aeronautical chart along which there is no angular difference between the magnetic and geographic north poles.
Air bleed (carburetor component)
A small hole in the fuel passage between the float bowl and the discharge nozzle of a float carburetor. Air drawn into the liquid fuel through the air bleed breaks the fuel up into an emulsion, making it easy to atomize and vaporize.
Air carrier
An organization or person involved in the business of transporting people or cargo by air for compensation or hire.
Air cooling
The removal of unwanted heat from an aircraft engine by transferring the heat directly into the air flowing over the engine components.
Air impingement starter
A turbine engine starter that basically consists of a nozzle that blows a stream of compressed air against the turbine blades to rotate the compressor for starting the engine.
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.
Air-oil separator
A component in a turbine engine lubrication system that removes the air from the scavenged oil before it is returned to the oil tank.
Air/fuel mixture ratio
The ratio of the weight of the air to that of the fuel in the mixture fed into the cylinders of an engine.
Aircraft
A device that is used or intended to be used for flight in the air.
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.
Aircraft engine
An engine that is used or intended to be used for propelling aircraft. It includes turbosuperchargers, appurtenances, and accessories necessary for its functioning, but does not include propellers.
Aircraft Specifications
FAA recordkeeping documents issued for both type-certificated and non-typecertificated products which have been found eligible for U.S. airworthiness certification.
Aircraft Surveillance Application (ASA)
An application that uses aircraft surveillance data to provide benefits to the flight crew (refer to Table 1).
Aircraft Surveillance Applications System (ASAS)
An aircraft system based on airborne surveillance that provides assistance to the flight crew in operating their aircraft relative to other aircraft. Airborne Surveillance and Separation Assurance Processing (ASSAP). The processing subsystem that accepts surveillance inputs (e.g., ADS-B reports), performs surveillance processing to provide reports and tracks, and performs application-specific processing. Surveillance reports, tracks, and any application-specific alerts or guidance are output by ASSAP to the CDTI function. ASSAP surveillance processing consists of track processing and correlation of ADS-B, TIS-B, ADS-R and TCAS reports.
Airfoil
Any device that creates a force, or lift, based on Bernoulli’s principles or Newton’s laws, when air is caused to flow over the surface of the device.
Airfoil
Any surface designed to obtain a useful reaction, or lift, from air passing over it.
Airframe
The fuselage, booms, nacelles, cowlings, fairings, airfoil surfaces (including rotors but excluding propellers and rotating airfoils of engines), and landing gear of an aircraft and their accessories and controls.
Airplane
An engine-driven fixed-wing aircraft heavier than air, that is supported in flight by the dynamic reaction of the air against its wings.
Airship
An engine-driven lighter-than-air aircraft that can be steered.
Airspeed indicator
A flight instrument that measures the pressure differential between the pitot, or ram, air pressure, and the static pressure of the air surrounding the aircraft. This differential pressure is shown in units of miles per hour, knots, or kilometers per hour.
Airworthiness certificate
A document required to be onboard an aircraft that indicates the aircraft conforms to type design and is in condition for safe operation.
Airworthiness Directive
Airworthiness Directives (ADs) are legally enforceable regulations issued by the FAA in accordance with 14 CFR part 39 to correct an unsafe condition in a product. Part 39 defines a product as an aircraft, engine, propeller, or appliance.
Airworthiness directive
A regulation issued by the FAA that applies to aircraft, aircraft engines, propellers, or appliances, when an unsafe condition exists and that condition is likely to exist or develop in other products of the same type design.
Airworthiness Directive (AD note)
Airworthiness Directives (ADs) are legally enforceable rules issued by the FAA in accordance with 14 CFR part 39 to correct an unsafe condition in a product. 14 CFR part 39 defines a product as an aircraft, aircraft engine, propeller, or appliance.
Airworthiness directive (AD)
Issued by the FAA in response to deficiencies and/or unsafe conditions found in aircraft, engines, propellers, or other aircraft parts. Compliance with an AD is mandatory.
Airworthy
When an aircraft or one of its component parts meets its type design and is in a condition for safe operation.
Alclad
A registered trade name for clad aluminum alloy.
Alclad aluminum
Used to designate sheets that consist of an aluminum alloy core coated with a layer of pure aluminum to a depth of approximately 51⁄2 percent on each side.
Alert
A general term that applies to all advisories, cautions, and warning information; can include visual, aural, tactile, or other attention-getting methods.
Algebra
The branch of mathematics that uses letters or symbols to represent numbers in formulas and equations.
All-weather spark plug
A shielded spark plug designed for high altitude operation. The ceramic insulator is recessed into the shell to allow a resilient grommet on the ignition harness to provide a watertight seal. All weather spark plugs, also called high-altitude spark plugs, are identified by their 3/4-20 shielding threads.
Allowance
The difference of the upper and lower variation of a part.
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.
Alodizing
A simple chemical treatment for all aluminum alloys to increase their corrosion resistance and to improve their paint bonding qualities.
Alpha control range (alpha mode)
The flight operating mode from takeoff through landing for a turbo-prop engine. Alpha mode includes operations from 95% to 100% of the engine’s rated rpm.
Alphanumeric symbols
Symbols made up of all of the letters in our alphabet, numerals, punctuation marks, and certain other special symbols.
Alteration
A change or modification to an aircraft from its previous state Alternating current. An electric current that reverses direction in a circuit at regular intervals.
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.
Altimeter setting
The barometric pressure at a given location corrected to mean (average) sea level.
Altitude engine
A reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.
Altitude engine
An aircraft reciprocating engine equipped with a supercharger that allows it to maintain its rated sea- level horsepower to an established higher altitude.
Altitude engine
A reciprocating engine whose rated sea-level takeoff power can be produced to an established higher altitude.
Alumel
An alloy of nickel, aluminum, manganese, and silicon that is the negative element in a thermocouple used to measure exhaust gas temperature.
Amateur-built aircraft
Aircraft built by individuals as a hobby rather than by factories as commercial products. Amateur-built or home-built aircraft do not fall under the stringent requirements imposed by the FAA on commercially built aircraft.
Ambient air pressure
The pressure of the air that surrounds an object.
Ambient light
The visible light level measured at the surface of the part.
Ambient pressure
The pressure of the air surrounding a person or an object.
Ambient temperature
The temperature of the air surrounding a person or an object.
American wire gauge
The system of measurement of wire size used in aircraft electrical systems.
Ammeter
An instrument for measuring electric current in amperes.
Ampere
A unit of measure of the rate of electron flow or current in an electrical conductor. One ampere of current represents one coulomb of electrical charge (6.24 × 1018 charge carriers) moving past a specific point in one second.
Ampere (A)
The basic unit of current flow. One A is the amount of current that flows when a difference of potential of 1 V is applied to a circuit with a resistance of 1 Ω. One coulomb per second.
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.
An airspeed indicator is a differential-pressure gauge
It measures the difference between static air pressure and pitot air pressure.
Analog electronics
Electronics in which values change in a linear fashion. Output values vary in direct relationship to changes of input values.
Analog indicator
An indicator that shows the value of the parameter being measured by a number marked on a graduated dial aligned with a movable pointer.
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 discs 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 between the chordline of a propeller blade and the relative wind. The angle of attack is affected by both the engine rpm and the forward speed of the aircraft.
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.
Annealing
The process of heating a metal to a prescribed temperature, holding it there for a specified length of time, and then cooling the metal back to room temperature.
Annual inspection
An inspection required by the FAA once every 12 calendar months if other suitable inspections do not occur within that timeframe. An A&P technician with inspection authorization must perform this inspection.
Annual inspection
A complete inspection of the airframe and powerplant required for FAA-certificated aircraft operating under 14 CFR part 91 General Operating and Flight Rules, and not on one of the authorized special inspection programs. An annual inspection must be conducted every 12 calendar months, and it must be conducted by an aviation maintenance technician who holds an Airframe and Powerplant rating and an Inspection Authorization. The scope of an annual inspection is the same as that of a 100-hour inspection.
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.
Annular duct
A duct, or passage, that surrounds an object. The annular fan-discharge duct surrounds the core engine.
Annular orifice
A ring-shaped orifice, normally one that surrounds another orifice.
Annulus
A ring or groove around the outside of a circular body or shaft, or around the inside of a cylindrical hole.
Annunciator panel
A panel of warning lights visible to the flight crew. The lights are identified by the name of the system they represent and are often covered with colored lenses. Red lights indicate a dangerous condition and green indicate a safe condition.
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 most common surface treatment of nonclad aluminum alloy surfaces. The aluminum alloy sheet or casting is the positive pole in an electrolytic bath in which chromic acid or other oxidizing agent produces an aluminum oxide film on the metal surface. Aluminum oxide is naturally protective, and anodizing merely increases the thickness and density of the natural oxide film.
Anodizing
A hard, airtight, unbroken oxide film electrolytically deposited on an aluminum alloy surface to protect it from corrosion.
Anodizing
The electrolytic process in which a hard, airtight, oxide film is deposited on aluminum alloy for corrosion protection.
Antenna
A device designed to radiate or intercept electromagnetic waves.
Antenna
Aspecial device used with electronic communication and navigation systems to radiate and receive electromagnetic energy.
Antenna Offset Parameter
The distance from the nose of the aircraft to the GPS antenna. For large aircraft, this offset is important in accurately placing the aircraft symbol on the airport map.
Anti-ice system
A system that prevents the formation of ice on an aircraft structure.
Anti-icing
Prevention of the formation of ice on a surface.
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.
Anti-propeller end
The end of a reciprocating engine that does not attach to the propeller. Also called the accessory end.
Anti-tear strips
Strips of fabric of the same material as the airplane is covered with, laid over the wing rib under the reinforcing tape.
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 brake 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.
Apparent power
That power apparently available for use in an AC circuit containing a reactive component. It is the product of effective voltage times the effective current, expressed in volt-amperes.
Apparent power
The product of volts and amperes in AC circuits where the current and voltage are out of phase.
Appliance
Any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory, including communications equipment, that is used or intended to be used in operating or controlling an aircraft in flight, is installed in or attached to the aircraft, and is not part of an airframe, engine, or propeller.
Appliance
Any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory, including communications equipment, that is used or intended to be used in operating or controlling an aircraft in flight, is installed in or attached to the aircraft, and is not part of an airframe, engine or propeller.
Application
The function(s) for which the ASA system is used.
Approved
Approved by the FAA or any person to whom the FAA has delegated its authority in the matter concerned, or approved under the provisions of a bilateral agreement between the United States and a foreign country or jurisdiction.
Aramid fiber
Fiber made from an organic compound of carbon, hydrogen, oxygen, and nitrogen. It has high strength and low density. It is flexible under load and is able to withstand impact, shock, and vibration. Kevlar is a well- known aramid fiber.
Arbor press
A press with either a mechanically or hydraulically operated ram used in a maintenance shop for a variety of pressing functions.
Archimedes’ principle
The buoyant force that a fluid exerts upon a submerged body is equal to the weight of the fluid the body displaces.
Arcing
Sparking between a commutator and brush or between switch contacts that is caused by induced current when a circuit is broken.
Area
A measurement of the amount of surface inside a two- dimensional object.
Area
The number of square units in a surface.
Area Navigation (RNAV)
A method of navigation that permits aircraft operation on any desired flight path within the coverage of station-referenced navigation aids or within the limits of the capability of self-contained aids, or a combination of these.
Arm
The horizontal distance that a part of the aircraft or a piece of equipment is located from the datum.
Arm
A measurement of distance, in inches, feet, etc., used in weight and balance calculations. Normally only the longitudinal arm is of practical importance. The three axial arms are longitudinal arm, lateral arm, and vertical arm.
Armature
The rotating part of an electric generator or motor.
Aromatic compound
A chemical compound such as toluene, xylene, and benzene that is blended with gasoline to improve its anti-detonation characteristics.
Articulating rod
See link rod.
Aspect ratio
The relationship of the length (wingtip to wingtip), or span, of an airfoil to its width, or chord.
Aspect ratio
The ratio of the length of an airfoil, such as a compressor blade, to its width.
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.
Assembly drawing
A description of an object made up of two or more parts.
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.
Asymmetrical loading
The loading of a propeller disc that causes one side to produce more thrust than the other side.
Atom
The smallest particle composed of a nucleus that contains protons, neutrons, and electrons, which revolve around the nucleus
Atomize
The process of breaking a liquid down into tiny droplets or a fine spray. Atomized liquids vaporize easily.
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.
Augmentor tube
A long, specially shaped stainless steel tube mounted around the exhaust tail pipe of a reciprocating engine. As exhaust gases flow through the augmentor tube, they produce a low pressure in the engine compartment that draws in cooling air through the cylinder fins.
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.
Autogyro
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 Autogyro 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 disc brake that compensates for disc 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 discs or the disc and lining is returned to a preset value. A malfunctioning automatic adjuster in a multiple-disc brake can cause sluggish and jerky operation.
Automatic Dependent Surveillance - Rebroadcast (ADS-R)
Retransmission of UAT ADS-B messages from aircraft on the 1090ES link and 1090ES messages on the UAT link. ADS-R ensures aircraft equipped with different links can receive messages from one another when equipped with ADS-B IN.
Automatic Dependent Surveillance Broadcast (ADS-B)
An advanced surveillance technology where ADS-B OUT equipped aircraft share position, altitude, velocity, and other information with ATC and other appropriately equipped aircraft.
Automatic Dependent Surveillance-Broadcast (ADS-B)
A function on an aircraft or surface vehicle operating within the surface movement area that periodically broadcasts its state vector (horizontal and vertical position, horizontal and vertical velocity) and other information. ADS-B is automatic because no external stimulus is required to elicit a transmission. It is dependent because it relies on on-board navigation sources and on-board broadcast transmission systems to provide surveillance information to other users.
Automatic Dependent Surveillance-Rebroadcast (ADS-R)
A service of the ground system that rebroadcasts ADS-B messages from one link technology onto another. For example, the SBS ground system provides ADS-R service to rebroadcast UAT messages on 1090 MHz and vice versa.
Automatic direction finder (ADF)
A radio receiver utilizing a directional loop antenna that enables the receiver to indicate the direction from which a radio signal is being received; also called a radio compass.
Automatic Flight Control System (AFCS)
A flight control system incorporating an automatic pilot with additional systems such as a VOR coupler, an ILS approach coupler, and an internal navigation system that is fully automatic, so the aircraft can be flown in a completely automatic mode.
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.
Automatic intake valve
An intake valve opened by low pressure created inside the cylinder as the piston moves down. There is no mechanical means of opening it.
Automatic mixture control (AMC)
The device in a fuel metering system, such as a carburetor or fuel injection system, that keeps the air/fuel mixture ratio constant as the density of air changes with altitude.
Automatic pilot (autopilot)
An automatic flight control device that controls an aircraft about one or more of its three axes. The primary purpose of an autopilot is to relieve the pilot of the control of the aircraft during long periods of flight.
Autorotation
A rotorcraft or powered-lift flight condition in which the lifting rotor is driven entirely by action of the air when the rotorcraft or powered-lift is in motion.
Autosyn system
The registered trade name of a remote indicating instrument system. An Autosyn system uses an electromagnet rotor, excited with 400-hertz AC, and a three- phase distributed-pole stator.
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.
Auxiliary rotor
A rotor that serves either to counteract the effect of the main rotor torque on a rotorcraft or to maneuver the rotorcraft about one or more of its three principal axes.
Availability
An indication of the ability of a system or subsystem to provide usable service. Availability is expressed in terms of the probability of the system or subsystem being available at the beginning of an intended operation.
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 science and technology of electronics as applied to aviation.
Avionics
The branch of technology that deals with the design, production, installation, use, and servicing of electronic equipment mounted in aircraft.
Axial bearing load
The load on a bearing parallel to the shaft on which the bearing is mounted. Thrust produces an axial load on a bearing.
Axial turbine
A turbine that is turned by a fluid flowing through it in a direction that is approximately parallel to the shaft on which the turbine wheel is mounted.
Axial-flow compressor
A type of compressor used in gas turbine engines. Air passes through the compressor in essentially a straight line, parallel to the axis of the compressor. The compressor is made of a number of stages of rotating compressor blades between stages of stationary stator vanes.
Axis of rotation
The center line about which a propeller rotates.
Azimuth
Angular distance measured on a horizontal circle in a clockwise direction from either north or south.
Azimuth
A horizontal angular distance, measured clockwise from a fixed reference direction to an object.
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