| A/P | Autopilot |
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| A/T | Autothrottle |
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| AAA | Anti-aircraft Artillery |
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| AAM | Air-to-air Missile |
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| ACARS | Aircraft Communication Addressing and Reporting System |
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| ADF | Automatic Direction Finder |
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| ADI | Attitude Direction Indicator |
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| aerodynamics | The physics of the movement of objects through air or gas |
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| aerofoil | A solid body such as a wing, rotor or propeller, designed to move through air and produce lift or thrust |
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| aeronaut | The pilot of a lighter-than-air aircraft, especially a balloon. |
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| aeronautics | The study, or science, of Flight |
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| aerospace | The study of the science and technology of travel in the space above the earth. Aerospace includes travel within the atmosphere as well as in space beyond the earth's atmosphere. |
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| AEW | Airborne Early Warning |
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| AFB | Air Force Base |
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| AFS | Air Force Station |
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| afterburner | Device that injects additional fuel into the specially designed jetpipe of a turbojet to provide augmented thrust. Also called reheat. |
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| AFTN | Aeronautic Fixed Telecommunications Network |
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| AGL | Above ground level |
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| aileron | Control surface attached to wingtip trailing edge (or between wingtips on some early biplanes) to provide control in roll about the aircraft's longitudinal axis. |
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| AIP | Aeronautical Information Publication |
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| airbrake | A surface that can be extended into the airflow to reduce an airplane's forward speed. |
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| airframe | The assembled structure of an aircraft, including system components forming an integral part of structure and influencing strength, integrity or shape. |
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| ALT | Altitude |
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| altimeter | Instrument for measuring an aircraft's altitude |
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| ALTN | Alternate |
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| amphibian | An aircraft capable of operating from land and water, and of transferring from one to the other |
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| AMRAAM | Advanced medium-range air-to-air missile |
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| angle of attack | The angle at which a wing meets the local undisturbed airflow. Not to be confused with angle of incidence |
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| angle of incidence | The fore-and-aft angle at which a wing or tailplane is attached to the fuselage, in relation to the aircraft's horizontal axis. Not to be confused with angle of attack. |
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| anhedral | The sloping downwards of a wing or tailplane from root to tip. |
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| AOA | Angle of attack |
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| APC | Armoured Personnel Carrier |
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| APU | Auxiliary Power Unit |
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| ARCC | Aeronautical Rescue Coordination Centre |
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| arrester hook | A strong hook attached to some land-based and all carrier-based aeroplanes to engage an arrester wire and thus shorten the landing run. |
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| ASI | Airspeed Indicator |
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| ASM | Air-to-surface Missile |
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| astrodome | A transparent dome in an aeroplane fuselage through which a navigator can navigate by the stars, using a sextant. |
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| ASW | Anti-submarine warfare |
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| ATA | Actual Time of Arrival |
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| ATC | Air Traffic Control |
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| ATIS | Automatic Terminal Information Service. A recorded voice message that provides weather and airport services information. |
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| attitude | An aircraft's flying position at a given time. |
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| autogyro | A rotorcraft propelled by a horizontal thrust system such as a propeller and lifted by an unpowered rotor free to spin under the action of the air flowing through its disc from below |
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| AWACS | Airborne Warning and Control System |
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