Glossary of Aviation Terminology


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Above ground level (AGL): Distance of the aircraft above the ground Synonyms: radar altitude;

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

Absolute: A standard, fixed reference, as opposed to moving reference; Compare: relative;

Acceleration: Rate of change of velocity, either scalar or vector, often with subscripts such as ENU or XYZ to denote the coordinate frame; time derivative of velocity; time integral of jerk; Symbols: a, A; Typical Units: ft/s-squared, g; Dimensions: Length / Time-squared;

Accelerometer: An inertial device for measuring acceleration, usually in three orthogonal axes (lateral X, longitudinal Y, and vertical Z); accelerometers usually consist of a mass, spring, and damper; accelerometers are usually included in inertial sensors, such as AHRS and INS;

ADC: Air data computer

ADDR: Air data dead reckoning

ADF: Automatic Direction Finding

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 (from MIL-STD-1472D); an annunciator that is the least critical (less than a caution or a warning);

AFCS: Automatic flight control system

AGL: Above ground level

AGR: Air-ground ranging

AGR slant range: Straight-line distance from the aircraft to a point on the ground;

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 Compare: update;

Aileron: A control surface on fixed-wing aircraft, usually mounted on the aft edge of wings, that controls roll, and is controlled by the wheel; Symbols: delta sub A; Typical Units: rad, deg;

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

Air-ground ranging (AGR): 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 definition for flight path angle; Compare: earth-referenced flight path angle; Symbols: gamma sub A; Typical Units: rad, deg;

Air Traffic Control (ATC): Standard aviation term

Aircraft (ac): A craft that flies in the air; either fixed or rotory wing.

Airspeed (as, a/s): See Also: state data, true airspeed, indicated airspeed, calibrated airspeed; Symbols: V sub A/S; Typical Units: kt, ft/s; Dimensions: Length / Time;

Airy: A standard model for computing earth data

Alignment: A basic control to a data source from controls and displays to align a device. Also a procedure to align physical devices, usually navigation sensors, so that they provide the most accurate results possible; commonly required by INS, AHRS, barometric altimeter; See Also: boresighting, calibration, initialization;

ALTINTVAL: Altitude integral input

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

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); Symbols: h; Typical Units: ft; Dimensions: Length;

Altitude error: A basic output from guidance to flight director, indicating the difference between actual altitude and desired altitude; Symbols: DELTA h; Typical Units: ft; Dimensions: Length

Altitude error scale factor (KZSF): A guidance control law parameter, generated by the vertical guidance modes; varies control authority of vertical guidance

Altitude integral gain (KALTINT): 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 error Typical Units: ft; Dimensions: Length;

Altitude integral input (ALTINTVAL): A guidance control law parameter, generated by the vertical guidance modes; a reference altitude for reducing steady-state errors in altitude error Typical Units: ft; Dimensions: Length;

Altitude integral limit (INTMAGLIM): A guidance control law parameter, generated by the vertical guidance modes; limits the magnitude of altitude integral value Typical Units: ft; Dimensions: Length;

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; Symbols: alpha; Typical Units: rad, deg;

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; Symbols: alpha; Typical Units: rad/s-squared; Dimensions: 1/Time-squared;

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; Synonyms: angle; Symbols: theta; Typical Units: rad, deg;

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; See Also: tachometer; Symbols: omega; Typical Units: rad/s, rpm; Dimensions: 1/Time;

Annunciator: Any one of warning, caution, or advisory; Synonyms: alert;

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

APPR: Approach

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; See Also: waypoint approach, ILS approach, rendezvous approach;

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

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; See Also: capture criterion; Compare: activate, capture;

ASL: Above sea level

Astronomical latitude: Latitude measured with respect to vector of apparent gravity; Compare: geocentric latitude, geodetic latitude; Symbols: Phi sub A; Typical Units: rad, deg,DMS;

ATC: Air Traffic Control

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

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

Attitude Heading Reference System (AHRS): 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 strapdwon accelerometers;

Automatic Direction Finding (ADF): A basic guidance mode, providing lateral guidance to a radio station. Equipment that determines bearing to a radio station;

Automatic flight control system (AFCS): An automated system for controlling the primary flight controls, often with built-in functions for guidance and flight director, and sometimes radio navigation; many flight control systems include basic instruments similar to a AHRS; 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; Synonyms: automatic flight control system;

Averaging filter: A filter for combining multiple data sources, usually of the same type, by adding with weighted averages; a simple average of the data sources; Compare: complementary filter, Kalman filter;

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


A , B , C , D , E , F , G , H , I , J - K , L , M , N , O , P , Q - R , S , T , U , V, W, X - Z