- AAM Air-to-air missle.
- AAR Air-to-air refuelling.
- AB Aktiebolag (Swedish company constitution).
- absolute ceiling Greatest altitude attainable by aircraft in level flight.
- AC Alternating current.
- ACC Air Combat Command (US).
- ACLS Automatic carrier landing system.
- ACMI Air combat manoeuvring instrumentation.
- ACN Aircraft classification number (ICAO system for aircraft pavements).
- ADC Air data computer.
- ADF Medium-frequency automatic direction-finding (equipment).
- ADI Attitude/director indicator.
- aerofoil Any solid body so shaped that, as a fluid medium (air or hot gas moves past it, it experiences a useful force perpendicular to the direction of relative motion; thus, a wing generates lift, while a turbine blade generates torque on a shaft.
- aeroplane (N America, airplane) Heavier-than-air aircraft with propulsion and a wing that does not rotate in order to generate lift.
- AEW Airborne early warning.
- AFB Air Force Base (USAF).
- AFCS Automatic flight control system.
- AFRC Air Force Reserve Command (US).
- AFRP Aramid fibre-reinforced plastics.
- afterburning Temporarily augmenting the thrust of a turbofan or turbojet by burning additional fuel in the jetpipe.
- AGM Air-to-ground missile.
- Ah Ampere-hours.
- AHRS Attitude/heading reference system.
- airbrake Passive device extended from aircraft to increase drag. Most common form is hinged flap(s) or plate(s), mounted in locations where operation causes no significant deterioration in stability and control at attainable airspeed.
- aircraft All manmade vehicles for off-surface navigation within the atmosphere, including helicopters and ballons. For practical purposes, air-cushion vehicles and wing-in-ground-effect vehicles are excluded from the classification.
- airship Power-driven lighter-than-air aircraft. Traditional classes are: blimp, a small non-rigid; non-rigid, in which envelope is essentially devoid of rigid members and maintains shape by inflation pressure; semi-rigid, non-rigid with strong axial keel acting as beam to support load; and rigid, in which envelope is itself stiff in local bending or supported within or around rigid framework.
- airstair Retractable stairway built into aircraft.
- ALARM Air-launched anti-radiation missile.
- ALCM Air-launched cruise missile.
- Allithium Aluminium-lithium alloy.
- ALLTV All-light level television.
- AM Amplitude modulation.
- AMC Air Mobility Command (US).
- AMRAAM Advanced Medium-Range AAM.
- ANG Air National Guard (US).
- anhedral Downward slope of wing or tailplane from root to tip.
- anti-balance tab Hinged surface on trailing-edge of stabilisator and operating in same direction, so as to dampen its movement.
- ANVIS Aviator's night vision system.
- AO Aktsionernoye Obshchestvo (Co Ltd; Russian company constitution).
- AoA Angle of attack (see 'attack' below).
- AOOT Aktsionernoye Obshchestvo Otkrytogo Tipa (Russian company constitution).
- approch noise Measured 1 n mile from downwind end of runway with aircraft passing overhead at 113 m (370 ft).
- APR Auxiliary power reserve.
- APU Auxiliary power unit (part of aircraft).
- ARINC Aeronautical Radio Inc, US company whose electronic box sizes (racking sizes) are the international standard.
- ARM Anti-radiation missile.
- ArNG Army National Guard (US).
- ASE (1) Automatic stabilisation equipment; (2) Aircraft survivability equipment.
- ASI Airspeed indicator.
- ASM Air-to-surface missile.
- aspect ratio Measure of wing (or other aerofoil) slenderness seen in plan view, usually defined as the square of the span divided by gross area.
- AST Air Staff Target (UK).
- ASTOVL Advanced STOVL.
- ASUW Anti-surface unit warfare.
- ASV Anti-surface vessel.
- ASW Anti-submarine warfare.
- ATC Air traffic control.
- ATR Airline Transport Radio ARINC 404 black box racking standards.
- attack, angle of (alpha) Angle at which airstream meets aerofoil (angle between mean chord and free-stream direction). Not to be confused with angle of incidence (which see).
- augmented Boosted by afterburning (turbofan).
- autogyro Rotary-wing aircraft propelled by a propeller (or other thrusting device) and lifted by a freely running autorotating rotor.
- AUW All-up weight (term meaning total weight of aircraft under defined conditions, or at a specific time during flight). Not to be confused with MTOW (which see).
- avionics Aviation electronics.
- AWACS Airborne warning and control system (aircraft category).
- axisymmetric intakes Twin, circular engine air intakes mounted astride the spinner of New Piper light aircraft.
- axisymmetric nozzle Circular jet-engine nozzle capable of unrestricted vectoring movement (within a cone specified by mechanical limitation) to enhance aircraft manoeuvrability.