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Above sea level (ASL): Distance of the aircraft above the average sea level.

Absolute: A standard, fixed reference, as opposed to moving reference.

Acceleration East: Aircraft acceleration in true east direction.

Acceleration North: Aircraft acceleration in true north direction.

Acceleration: Rate of change of velocity, either scalar or vector.

Accelerometer: An inertial device for measuring acceleration, usually in three orthogonal axes; accelerometers usually consist of a mass, spring, and damper; accelerometers are usually included in inertial sensors, such as AHRS and INS.

Accept: Granted the ability to proceed with a position update usually by an operator.

Accuracy: Measure of exactness, possibly expressed in percent.

Acquire: To begin reception of useful data

Activate: To begin performing a mission objective, such as flying along a radial of a radio station; usually refers to a mode of radio navigation, such flying along that radial after capturing that radial.

ADC: Air data computer.

ADDR: Air data dead reckoning.

ADF: Automatic Direction Finding.

Administrator: The Federal Aviation Administrator or any person to whom he has delegated his authority in the matter concerned.

Advisory: A signal to indicate safe or normal configuration, condition of performance, operation of essential equipment, or to attract attention and impart information for routine action purposes.

AFCS: Automatic flight control system.

Affidavit: A written statement under oath.

AGL: Above ground level.

AGR Slant Range: Straight-line distance from the aircraft to a point on the ground.

AGR: Air-ground ranging.

Agreement: Mutual assent between two or more parties; normally leads to a contract; may be verbal or written.

AHOV: Approach to hover.

AHRS: Attitude Heading Reference System.

Aiding: A process by which one or more sensors provide data to another sensor to produce results better than any single sensor; aiding occurs at the data source level or at the physical device level, depending upon specific implementation of the device and the data source (choice of implementation is transparent above the data source); aiding is automatically controlled by software without input from an operator; a basic control to a data source from navigation, radio navigation, or other devices.

Aileron: A control surface on fixed-wing aircraft, usually mounted on the aft edge of wings, which controls roll, and is controlled by the wheel.

Air Carrier: A person who undertakes directly by lease, or other arrangement, to engage in air transportation.

Air Commerce: Interstate, overseas, or foreign air commerce or the transportation of mail by aircraft or any operation or navigation of aircraft within the limits of any Federal airway or any operation or navigation of aircraft which directly affects, or which may endanger safety in, interstate, overseas, or foreign air commerce.

Air Data Computer (ADC): A primary navigation data source used in Aviation. A navigation sensor based on atmospheric data sensors; usually measures static pressure, dynamic pressure, and outside air temperature; sometimes computes other atmospheric data, such as indicated airspeed, Mach number, calibrated airspeed, as a guidance mode, ADC is least accurate of the listed modes and is used only as a last resort.

Air Data Dead Reckoning: Dead reckoning navigation based on simple instruments as source (barometric altimeter, magnetic compass, airspeed indicator, known wind conditions); sometimes called dead reckoning.

Air Taxi: An aircraft operator who conducts operations for hire or compensation in accordance with FAR Part 135 in an aircraft with 30 or fewer passenger seats and a payload capacity of 7,500 or less. An air taxi operates on an on demand basis and does not meet the "flight scheduled" qualifications of a commuter.

Air Traffic Clearance: An authorization by air traffic control, for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified traffic conditions within controlled airspace.

Air Traffic Control: A service operated by appropriate authority to promote the safe, orderly, and expeditious flow of air traffic.

Air Traffic Control: Standard aviation term used for the team of people that direct the planes, develop flight patterns and stress the alleviation of aviation accidents.

Air Traffic: Aircraft operating in the air or on an airport surface, exclusive of loading ramps and parking areas.

Air Transportation: Interstate, overseas, or foreign air transportation or the transportation of mail by aircraft.

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: A craft that flies in the air; either has fixed or rotary wings.

Aircraft: A device that is used or intended to be used for flight in the air.

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.

Air-Ground Ranging: Straight-line distance from the aircraft to a point on the ground.

Air-Mass Flight Path Angle: Angle in vertical plane of earthspeed vector and groundspeed vector; occasional is used as the definition for flight path angle.

Airplane: An engine-driven fixed-wing aircraft heavier than air, which is supported in flight by the dynamic reaction of the air against its wings.

Airport: An area of land or water that is used or intended to be used for the landing and takeoff of aircraft, and includes its buildings and facilities, if any.

Airship: An engine-driven lighter-than-air aircraft that can be steered.

Airy: A standard model for computing earth data.

Alert Area: An alert area is established to inform pilots of a specific area wherein a high volume of pilot training or an unusual type of aeronautical activity is conducted.

Alignment: A basic control to a data source from controls and displays to align a device. Alignment may also be referred to as a procedure to align physical devices, usually navigation sensors, so that they provide the most accurate results possible.

Alternate Airport: An airport at which an aircraft may land if a landing at the intended airport becomes inadvisable.

Altimeter: A device to measure altitude, either barometric altitude or radar altitude

ALTINTVAL: Altitude integral input.

Altitude Engine: A reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.

Altitude Error Scale Factor: A guidance control law parameter, generated by the vertical guidance modes; varies control authority of vertical guidance.

Altitude Error: A basic output from guidance to flight director, indicating the difference between actual altitude and desired altitude.

Altitude Integral Gain: A guidance control law parameter, generated by the vertical guidance modes; varies control authority of the altitude integral in vertical guidance, to reduce steady-state errors in altitude situations.

Altitude Integral Input: A guidance control law parameter, generated by the vertical guidance modes; a reference altitude for reducing steady-state errors in altitude situation.

Altitude Integral Limit: A guidance control law parameter, generated by the vertical guidance modes; limits the magnitude of altitude integral.

Altitude: Height, usually with respect to the terrain below (radar altitude, feet above closest dirt) or fixed earth reference (barometric altitude, feet above mean sea level).

Angle of Attack: The difference between pitch and the air-referenced flight path angle; the angle between the aircraft center line and the airspeed vector in the vertical plane, positive when the nose is up.

Angular Acceleration: Rate of change of angular velocity, either scalar or vector, often with subscripts such as XYZ to denote the coordinate frame; time derivative of angular position; time integral of angular acceleration.

Angular Position: Amount of rotation about an axis, either scalar or vector, often with subscripts such as XYZ to denote the coordinate frame; time integral of angular velocity.

Angular Velocity: Rate of change of rotation about an axis, either scalar or vector, often with subscripts such as XYZ to denote the coordinate frame; time derivative of angular position; time integral of angular acceleration.

Annunciator: Any one of warning, caution, or advisory; synonyms with alert.

Answer: Pleading filed by the defendant that responds to a complaint, petition, or motion.

Aperiodic: A process that executes based on events rather than a fixed rate, it is not synchronized to other processes of interest.

Appeal: A request to the higher court for review of the lower court’s decision and to request a reversal of the judgment.

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.

Approach (APPR): To fly towards a point; a basic guidance mode, providing lateral guidance, longitudinal guidance, and vertical guidance to a point at an operator selected groundspeed and radar altitude.

Approach to Hover (AHOV): Hover approach of a rotary wing aircraft.

Arbitration: The procedure by which a dispute may be resolved by a person who is not a judge. Arbitration is often used to limit legal costs to both parties.

Arbitrator: A person who conducts an arbitration.

Area Navigation: A method of navigation that permits aircraft operations on any desired course within the coverage of station-referenced navigation signals or within the limits of self-contained system capability.

Arm: To strive for a mission objective, such as flying toward a radial of a radio station; usually refers to a mode of radio navigation, such as striving to reach a specific radial of a radio station prior to flying along that radial.

ASL: Above sea level.

Assumption of Risk: A doctrine that states if the plaintiff has knowingly accepted the danger of doing something, recovery from the defendant in an action brought for negligence will be barred.

Astronomical Latitude: Latitude measured with respect to vector of apparent gravity;

ATC: Air Traffic Control.

Atmospheric Data: Environmental data related to the atmosphere at some point of interest.

Attitude Heading Reference System: Combines information from a Magnetic Heading Sensor with self-contained aircraft acceleration data to provide attitude, heading, position, body inertial velocity, and body inertial acceleration. Typically a low-accuracy, self-contained navigation source using strap-down accelerometers.

Attitude: The primary aircraft angles in the state vector; pitch, roll, and yaw.

Australian National: A standard model for computing earth data.

Automatic Direction Finding: A basic guidance mode, providing lateral guidance to a radio station.

Automatic Flight Control System: An automated system for controlling the primary flight controls, often with built-in functions for guidance and flight direction and sometimes radio navigation. Many flight control systems accept flight director inputs so that its radio navigation, guidance, and flight director can be bypassed.

Autopilot: A mode of an automatic flight control system which controls primary flight controls to meet specific mission objectives, such as maintain a heading or altitude.

Averaging Filter: A filter for combining multiple data sources, usually of the same type, by adding with weighted averages.

Aviation Trust Fund: A federal reserve of tax monies levied on airline tickets and operations and set aside to improve the U.S. air transportation system.

AVM: Avionics monitor.

Axis: One direction in an orthogonal reference frame.

Azimuth: An angle in the horizontal plane, usually measured with respect to body coordinates.