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.
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 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.
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.
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.
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.
Agonic line
A line drawn on an aeronautical chart along which there is no angular difference between the magnetic and geographic north poles.
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.
Airfoil
Any surface designed to obtain a useful reaction, or lift, from air passing over it.
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 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.
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.
Altimeter setting
The barometric pressure at a given location corrected to mean (average) sea level.
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.
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.
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-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 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
Aspecial device used with electronic communication and navigation systems to radiate and receive electromagnetic energy.
Anti-ice 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 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.
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.
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 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 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.
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.
Restrict the list to specific publications by clicking on the menubar at the top of the screen.