Aviation Terminology

8/8/2019 Aviation Terminology

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Glossary

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 todenote the coordinate frame; time derivative of velocity; time integral of jerk; Symbols: a, A;

Typical Units: ft/s-squared, g;Dimensions: Length / Time-squared;

Acceleration east.

Aircraft acceleration in true east direction; Symbols: A sub E; Typical Units: ft/s-squared;Dimensions: Length / Time-squared;

Acceleration north.

Aircraft acceleration in true north direction; Symbols: A sub N; Typical Units: ft/s-squared;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;

Accept.

To allow to proceed, for example with a position update, usually by an operator; Compare: reject


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Accuracy.

Measure of exactness, possibly expressed in percent; Compare: precision

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; SeeAlso: capture criterion; Compare: arm, capture;

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 ofessential equipment, or to attract attention and impart information for routine action purposes

(fromMIL-STD-1472D); an annunciator that is the least critical (less than a caution or awarning);

AFCS.

Automatic flight control system

AGL.

Above ground level

AGR.

Air-ground ranging

AGR slant range.


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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 betterthan 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 ofimplementation 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, radionavigation, 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; sometimescomputes 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 deadreckoning;

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 forflight path angle; Compare: earth-referenced flight path angle; Symbols: gamma sub A; Typical

Units: rad, deg;


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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 toalign 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).


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A guidance control law parameter, generated by the vertical guidance modes; varies controlauthority of vertical guidance

Altitude integral gain (KALTINT).

A guidance control law parameter, generated by the vertical guidance modes; varies controlauthority of the altitude integral in vertical guidance, to reduce steady-state errors in altitudeerrorTypical Units: ft;Dimensions: Length;

Altitude integral input (ALTINTVAL).

A guidance control law parameter, generated by the vertical guidance modes; a reference altitudefor reducing steady-state errors in altitude errorTypical Units: ft;Dimensions: Length;

Altitude integral limit (INTMAGLIM).

A guidance control law parameter, generated by the vertical guidance modes; limits themagnitude 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 todenote 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 angularacceleration; See Also: tachometer; Symbols: omega; Typical Units: rad/s, rpm;Dimensions:

1/Time;

Annunciator.


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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;C

ompare: 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 refersto 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.


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

Attitude Heading Reference System (AHRS).

Combines information from aMagnetic 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;

Australian National.


Automatic Direction Finding (ADF).

A basic guidance mode, providing lateral guidance to a radio station. Equipment that determinesbearing 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 systemsinclude 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 flightcontrol system;

Averaging filter.

A filter for combining multiple data sources, usually of the same type, by adding with weightedaverages; 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


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BALT SEL.

Barometric altitude select

Band-pass filter (BPF).

A filter that allows frequencies between two cutoff frequencies to pass while attenuating

frequencies outside the cutoff frequencies; a band-pass filter can be constructed as thecomposition of a low-pass filter and a high-pass filter;

Bank angle.

The angle between the horizontal plnase and the right wing in the lateral plane, positive when the

right wing is down; Synonyms: roll; Symbols: phi,Phi; Typical Units: rad, deg;

Barometric altitude.

Height with respect to fixed earth reference (above mean sea level); Synonyms: pressure altitude;

Symbols: h sub b; Typical Units: ft;Dimensions: Length;

Barometric altitude select (BALT SEL).

A basic guidance mode, providing vertical guidance to an operator selected barometric altitude;

Barometric pressure.

Height with respect to fixed earth reference (barometric altitude, feet above mean sea level);

Synonyms: pressure; Symbols: p sub a; Typical Units: in HG,mbar;Dimensions:M

ass /Time-squared * Length;

BC.

Bus controller

Beacon.

A device, usually based on the ground, that aids in determining position or direction;

Bearing (BRG).

Direction on a compass; Synonyms: direction; Symbols:B; Typical Units: rad, deg;

Bessel 1841.



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Bias.

An offset applied to a measurement for error correction; Synonyms: offset

BIS.

Built-in simulation

Body.

The aircraft, usually referring to a coordinate system;

Body coordinates.

Coordinates referenced to the body of the aircraft; See Also: XYZ; Compare: earth coordinates,stability coordinates

Boresight angle.

The angle between the center line of a sensor and aircraft center line, either by design or bymisalignment;

Boresighting.

A basic control to a data source from controls and displays to boresight a device; Also, a

procedure to align the center line of physical devices, usually update sensors, so that theyprovide the most accurate results possible; a basic control to a data source from controls and

displays; commonly required by FLIR

,MMR

; boresight procedures commonly result incorrection factors to be downloaded from the host processor to the device; during boresighting,

the device is usually not available; See Also: alignment, calibration, initialization;

BPF.

Band-pass filter

BRG.

Bearing

Built-in simulation (BIS).

Function in avionics software that simulates sensors, aircraft, and pilot, to exercise avionicssoftware (including navigation, radio navigation, guidance and flight director); BIS is often used

by a development team to check basic operation following installation of new software orpatches; BIS is seldom used by aircraft flight crews or maintenance crews; Compare: real-time

engineering simulation;


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Bus controller (BC).

Term defining role of device on a MIL-STD-1553 bus as being master; Compare: remoteterminal;

Calibrated airspeed (CAS).

Indicated airspeed corrected for instrumentation errors, but not for air density; See Also:airspeed; Symbols: V sub 'CAS'; Typical Units: kt,ft/s;Dimensions: Length / Time;

Calibration.

A basic control to a data source from controls and displays for calibrating a device; Also, a

procedure to adjust physical devices so that they provide the most accurate results possible;calibration procedures commonly result in correction factors to be downloaded from the host

processor to the device; during calibration, the device is usually not available; See Also:

alignment, boresighting, initialization;

Cant angle.

Angle of nacelle mounting; Typical Units: rad, deg;

Capture.

To attain an objective, such as reaching a radial of a radio station; See Also: capture criterion;

Compare: activate, arm;

Capture criterion.

A test case to determine if an armed objective has been captured; In avionics, an aircraft mighthave an objective to fly to a radial of a radio station, then to fly along it. While enroute, the

objective is armed, meaning that the crew and software are attempting to reach the radial. Theradial is captured and the objective is met when the capture criteria are met. In this case, the

capture criterion might be bearing to the radio station is within 5deg of 270deg. An objective canhave multiple criteria. Capture criterion are often used with radio navigation to determine a

transition from armed to active.

CAS.

Calibrated airspeed

Caution.

A signal which alerts the operator to an impending dangerous condition requiring attention, butnot necessarily immediate action (fromMIL-STD-1472D); an annunciator that is more critical

than an advisory but less critical than a warning;


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CCLIM.

Course cut limit

Center line.

Standard aviation term

CEP.

Circular error probability

Channel.

A number that maps to a frequency;

Circular error probability (CEP).

A probability that a percentage of two-dimension measurements will lie within a circle of given

radius, with the circle centered at truth or mean of the measurements; Compare: radial errorprobability, spherical error probability; CEP specifies test cases for measurement errors of

sensors of two dimensions, such as velocity east and north.

Clarke 1866.


Clarke 1880.


Collective.

A flight control operated by moving up or down with hand in rotary-wing aircraft, primarily tocontrol lift (altitude); controls collective (total) pitch of the rotors on a rotary-wing aircraft;

Collective cue.

A vertical flight director cue for rotary-wing aircraft, primarily to control altitude, by changingpower; Compare: yoke cue; Symbols: Gamma sub 'VERT'; Typical Units: percent,in;

Commanded.

Controls given to a device, not that the device necessarily obeyed the controls

Communications.


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How well equipment is communicating; Values: operational, degraded, failed

Complementary filter.

A filter in which the complement of the filter is desired, giving the effect of a high-pass filter by

implementing a low-pass filter; a filter for combining multiple data sources, usually of differenttypes, by adding filtered values, where the sum of the filters in the frequency domain is unity; aKalman filter with fixed gains; Complementary filters are often designed in the frequency

domain in way that that the filters determined at build time such that the cutoff frequency of theLFP is equal to that of the HPF. This provides the advantages of DNS's long-term accuracy and

INS's short-term accuracy, while filtering DNS's high-frequency noise and INS's slow drift.Compare: averaging filter, Kalman filter;

Computer cycle.

In a periodic, cyclical computer system, the most basic, fastest timing loop

Continuous time.

Time which can have any point expressed as a real quantity, without regard for any specific

interval or processing rate; Compare: discrete time;

Continuous-time equation.

A mathematical relationship to describe a function of time, expressed in terms of continuoustime; Compare: difference equation, differential equation, discrete-time equation, Laplace

transform, state-space model, Z transform; See Also: first-order filter, second-order filter, unit

functions for examples;

Control law.

The mathematical definition of a system used to control or to change the dynamic response of asystem;

Control surface.

An airfoil attached to an aircraft that is moved to control the attitude of the aircraft; an surface tocontrol flight of an aircraft indirectly, such as a swashplate to control pitch of rotor blades; See

Also: aileron, rudder, spoiler, elevator, flaps, trim tab, stabilizer; Symbols: delta; Typical Units:rad, deg;

Controlled altitude (CTALT).

A guidance control law parameter, generated by the vertical guidance modes; altitude that is

being controlled Typical Units: ft;Dimensions: Length;


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Controlled speed (CTS).

A guidance control law parameter, generated by the longitudinal guidance modes; speed that isbeing controlled Typical Units: ft/s, kt;Dimensions: Length / Time;

Coriolis acceleration.

Tangential acceleration caused by motion on a radial on a rotating surface, in aviation, it isacceleration in the earth's longitudinal direction caused by changing latitude, usually computed

from system state data; Symbols: a sub c; Typical Units: ft/s-squared,g;Dimensions: Length /Time-squared;

Corrected altitude.

Measured pressure altitude corrected for instrumentation errors

Coupled.

Describes operation of flight director in which automatic flight control system causes flightcontrols to follow commands from flight director or errors from guidance

Course.

Towards a point at a specified course; Compare: direct

Course cut limit (CCLIM).

A guidance control law parameter, generated by the lateral guidance modes; limits the interceptangle of the flight path with a desired course, typically 45deg Typical Units: deg, rad;

Creeping line search.

A pattern of equally spaced parallel lines followed for searching the ground from an aircraft;Compare: expanding square search, sector search;

Cross track.

Perpendicular to the course;

Crosstrack deviation (XTKD).

A guidance control law parameter, generated by the lateral guidance modes; distance from theaircraft to a desired course measured along a prependicular to the course Typical Units: ft;

Dimensions: Length;

Crosstrack deviation gain (KXTKD).


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A guidance control law parameter, generated by the lateral guidance modes; relative weightingof crosstrack deviation in the lateral control law Typical Units: rad/ft;Dimensions: 1/L;

Crosstrack deviation rate (XTKR).

A guidance control law parameter, generated by the lateral guidance modes; rate of change ofcrosstrack deviation Typical Units: ft/s;Dimensions: Length / Time;

Crosstrack deviation rate gain (KXTKR).

A guidance control law parameter, generated by the lateral guidance modes; relative weighting

of the crosstrack deviation rate in the lateral control law Typical Units: s;Dimensions: Time;

CTALT.

Controlled altitude

CTS.

Controlled speed

Cue.

A indicator to an operator for control placement, tells the operator where to place controls;Synonyms: command

Cursor.

See: moding cursor, target cursor

Cutoff frequency.

The frequency at which the gain of a filter is at an edge of a band, usually taken to be when gainis 0.5, or -3.01dB; the frequency at which the output of a filter is half the power of the input; See

Also: band-pass filter, high-pass filter, low-pass filter; Symbols: omega sub c; Typical Units:rad/s,Hz;Dimensions: 1/Time;

Cyclic.

See: longitudinal cyclic, lateral cyclic;

Damped frequency.

The frequency of oscillation of an underdamped second-order filter; See Also: second-order

filter; Symbols: omega; Typical Units: rad/s,Hz;Dimensions: 1/Time;


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Damping ratio.

Control parameter for a second order filter. Symbols: zeta;

Data source object (DSO).

Software that receives data from a physical device, translates the data into standard units,

maintains equipment status, and provides a common interface for each variation of a particulardevice;

Data Transfer System (DTS).

A device for transferring data with avionics, similar to a diskette drive;

Dead reckoning (DR).

A method of navigation based on basic information (barometric altitude, magnetic heading,airspeed, wind conditions) from best available source; sometimes short for air data dead

reckoning;

Delta.

Difference; error.

Depart from hover (dhov).

A guidance mode providing lateral guidance, longitudinal guidance and vertical guidance for a

set heading or bank angle, a set speed, and a set climb rate, altitude or pitch;

Derivative.

Rate of change, usually with respect to time; Symbols: x dot, x prime, x sup (1), dx/dt, Dx;

Derived.

Calculated values for which no direct measurement exists; Compare: estimated, filtered,measured, raw, selected, smoothed

DESALT.

Desired altitude

Desired.

What must be achieved in order to match a plan; Synonyms: reference;


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Desired altitude (DESALT).

A guidance control law parameter, generated by the vertical guidance modes; altitude whichcontrolled altitude is attempting to achieve Typical Units: ft;Dimensions: Length;

Desired path.

A trajectory in space determined by guidance to meet the current mission objectives;

Desired speed (DESS).

A guidance control law parameter, generated by the longitudinal guidance modes; speed whichcontrolled speed is attempting to achieve Typical Units: ft/s,kt;Dimensions: Length / Time;

DESS.

Desired speed

Deviation.

Difference from desired;

Device.

A piece of equipment, a subsystem; Synonyms: physical device, unit

DFAD.

Digitized Feature Analysis Data

DHOV.

Depart from hover

DME.

DistanceMeasuring Equipment

Difference equation.

A mathematical relationship to model a discrete function, expressed in terms of other values inthe sequence; Difference equations are usually derived from differential equations. Compare:

continuous-time equation, differential equation, discrete-time equation, Laplace transform, state-space model, Z transform; in avionics, a difference equation usually models periodic process in

terms of past values; See Also: first-order filter, integrator, second-order filter;


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Differential equation.

A mathematical relationship to model a continuous function, expressed in terms of derivatives;Initial conditions are usually given or implied. In avionics, differential equations are commonly

used by systems engineers to model avionics systems. The systems engineer usually converts

differential equations to difference equations for specification and implementation in software. Inavionics, a differential equation usually models continuous-time phenomenon in terms of timederivatives; Compare: continuous-time equation, difference equation, discrete-time equation,

Laplace transform, state-space model, Z transform; See Also: first-order filter, integrator, second-order filter

Digital Map Generator (DMG).

Digitial equipment that produces map video, and sometimes contains TRN; uses Digital TerrainElevation Data and Digitized Feature Analysis Data; Displays reconstructed digital map data,

aeronautical charts or photographs. The digital map data can be annotated with natural and man-

made (point and linear) features as well as threats. A TerrainR

eferenced Navigation algorithmcorrelates altitude readings with digital map data to provide position data.

Digital Terrain Elevation Data (DTED).

On a digitial map, data for elevation of terrain; DTED is usually provided by DefenseMappingAgency; Compare: Digitized Feature Analysis Data;

Digitized Feature Analysis Data (DFAD).

On a digitial map, data for cultural features such as buildings and roads; DFAD is usually

provided by DefenseM

apping Agency;C

ompare: Digital Terrain Elevation Data;

Dimensionless.

No units, such as ratios; Synonyms: unitless;

Direct.

Towards a point along the shortest distance; Compare: course

Direction.

bearing.

Discrete time.

Time divided into quantized intervals; in avionics, time is usually divived into equal intervals tocreate a periodic process; Compare: continuous time;


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Discrete-time equation.

A mathematical relationship to describe a function of time, expressed in terms of discrete time;Compare: continuous-time equation, difference equation, differential equation, Laplace

transform, state-space model, Z transform; See Also: first-order filter, unit functions;

Distance.

Method of measurement dependent on use; Synonyms: range;

Distance Measuring Equipment (DME).

Equipment for measuring distance, usually from an aircraft to a ground station; usually part of a

Tactical Air Navigation system

DMG.

DigitalMap Generator

DNS.

Doppler Navigation System

Doppler.

A technique for measuring velocity by radiating and determining frequency shift

Doppler Navigation System (DNS, DPLR).

A navigation for measuring velocity by radiating and determining frequency shift;

DPLR.

Doppler navigation system

DR.

Dead reckoning

Drag.

Force of air against aircraft acting in opposite direction of the airspeed vector projected into

horizontal plane; Symbols: D; Typical Units: lbf,kip;Dimensions:Mass * Length / Time-squared;

Drift.


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Slow, monotonic change in measured data

DSO.

Data source object

DTED.

Digital Terrain Elevation Data

DTS.

Data TransferSystem

Dynamic pressure.

Total pressure

Earth coordinates.

Coordinates referenced to the earth; See Also: east-north-up; Compare: body coordinates,

stability coordinates

Earth data.

Environmental data related to the earth at some point of interest; usually a function of latitude

and longitude

Earth eccentricity.

A measure of the degree to which the earth is oblate; Symbols: epsilon;

Earth model.

The earth model computes data related to the earth. Most data is a function of position. Standard

models are: International, Clarke 1866, Clarke 1880, Everest, Modified Everest, Bessel 1841,Australian National, World Geodetic Survey 1972, World Geodetic Survey 1984, Airy, Hough,

South American.

Earth radius.

Radius of the earth, function of position, separate radii for longitudinal radius and for lateral

radius; See Also: state data; Symbols: rho; Typical Units: ft;Dimensions: Length;

Earth radius best sphere.


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Gaussian radius of curvature

Earth radius east/west.

Prime radius of curvature

Earth radius north/south.

Meridian radius of curvature

Earth-referenced flight path angle.

Angle in vertical plane of airspeed vector and groundspeed vector; usual definition for flight pathangle; Compare: air-mass flight path angle; Symbols: gamma sub T; Typical Units: rad, deg;

Earthspeed.

Total velocity measured with respect to a plane tangent to the earth's surface at the current

position; a vector composed of velocity north, velocity east, and vertical velocity; See Also: statedata; Symbols: V sub E; Typical Units: kt,ft/s;Dimensions: Length / Time;

East-north-up (ENU).

A standard earth coordinate frame and sign convention, where east, north, and up are positive;vertical, or V, is sometimes used in place of up; Synonyms: east-north-vertical; Compare: XYZ;

East-north-vertical (ENV).

East-north-up.

ECI.

Earth Centered Inertial

Elevation.

An angle in the vertical plane through a longitudinal axis; height above mean sea level, usually

of terrain;

Elevator.

A control surface on fixed-wing aircraft, usually mounted on the aft edge of stabilizers, that

controls pitch, and is controlled by the yoke; Symbols: delta sub E; Typical Units: rad, deg;

ENU.


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East-north-up

ENV.

East-north-vertical

Environmental data.

Atmospheric data and earth data

Equipment status.

Operational status of a piece of equipment consisting of a status indicator and status words;Synonyms: health;

Error.

Difference between desired and measured data; Synonyms: delta;

Estimated.

Data that is the result of filtering two or more signals; Compare: derived, filtered, measured,raw, selected, smoothed

Euler angles.

Pitch, roll, and yaw

Euler parameters.

Four parameters for specifiying quaternions; Symbols: e sub < 1 , 2 , 3 , 4 >,a,b,c,s;

Everest.


Expanding square search.

A pattern of progressively larger squares (a ``square spiral'') followed for searching the groundfrom an aircraft; Compare: creeping line search, sector search;

Extrapolate.

Function to determine values from two or values in a table, when the given value lies outside of

the range of the table; usually linear but can be higher order;


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FCS.

Flight control system

Filter.

A device to alter a signal; software to alter a data steam; See Also: averaging filter, band-pass

filter, complementary filter, first-order filter, high-pass filter, hysteresis, Kalman filter, limiter,low-pass filter, rate limiter, second-order filter, smoothing filter, wash-out filter;

Filtered.

Data that is the result of filtering a signal; filtering is usually more sophisticated than smoothing

Compare: derived, estimated, measured, raw, selected, smoothed;

First-order filter.

A filter in which the output follows the input, only more slowly; It is usually implemented in

software as a difference equation of period T. The first-order filter is commonly used in avionicsto smooth data, and to wash out transients at mode change. It is also used as a low-pass filter.

When implementing a second-order filter on normalized variables, such as angles, thediscontinuities require special treatment.

Fix.

A determination of one's position based on external data, such as a known terrain point

Fixed wing.

An airplane, as opposed to a rotory wing / helicopter;

Flaps.

A control surface on fixed-wing aircraft, usually mounted to the fore edge of the wings, that

extends the wing to provide added lift at low speeds; Compare: slats; Symbols: delta sub F;Typical Units: rad, deg,percent;

Flight control system (FCS).

A primary flight control system or an automatic flight control system;

Flight controls.

Controls in a cockpit for flying an aircraft; primary flight controls are wheel, yoke, cyclic,pedals, throttle, and collective; secondary flight controls are flight controls other than primary,

such as flaps, slats, stabilizer, and landing gear;


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Flight director.

System, usually software, that generates stick position cues from state errors - typically threecues:. pitch, roll, and throttle for fixed-wing and longitudinal cyclic, lateral cyclic, and collective

for rotory wing;

Flight path angle (FPA).

Angle in vertical plane of earthspeed vector and groundspeed vector (usual definition), earth-

referenced flight path angle; angle in vertical plane of airspeed vector and groundspeed vector(occasional definition), air-mass flight path angle; Symbols: gamma; Typical Units: rad, deg;

Flight plan.

A predetermined route, possibly including guidance modes, communications, and mission

objectives, used by guidance and mission management for moding and planning; Series of

navigation reference points, waypoints, and mode commands for navigation, radio navigation,guidance, and flight director

FLIR.

Forward-Looking Infrared

Flux valve.

A device to measure the earth's magnetic flux; a compass

Fly over.

A position update by flying directly over a known point

Forward-Looking Infrared (FLIR).

Sensor equipment used to supplement AGR, extend the aircraft visual search capability and

provide position information for guidance and navigation update capability. Imagery derivedfrom the FLIRsensor is displayed in the cockpit. FLIRpointing can be controlled manually

using a tracking handle or automatically by theMission Computer. FLIRconverts a heat imageinto a video image and determines azimuth, elevation, and sometimes range of a point;

Synonyms: Infrared DetectingS

et;

FPA.

Flight path angle

GA.


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Go around

Gaussian radius of curvature.

Radius of the earth for the best fitting sphere at a given position; Synonyms: earth radius best

sphere; Symbols: rho sub G; Typical Units: ft;Dimensions: Length;

GCLP.

Guidance control law parameter

Geocentric latitude.

Latitude measured with respect to horizontal through mass center of the earth; Compare:

astronomical latitude, geodetic latitude; Symbols: Phi sub C; Typical Units: rad, deg; Reference:Kayton69. page 16

Geodetic latitude.

Latitude measured with respect to normal to reference ellipsoid; Compare: astronomical latitude,

geocentric latitude; Symbols: Phi sub T; Typical Units: rad, deg; Reference: Kayton69. page 16

Gimbaled inertial sensor.

Accelerometers mounted to a platform which is free to rotate, with gyroscopes to measure

rotation and servomotors to maintain a fixed attitude with respect to the earth Compare:strapdown inertial sensor;

Glideslope.

Angle approach a runway; Symbols: Gamma; Typical Units: rad, deg;

Global Positioning System (GPS).

A navigation sensor based on satellites; A Global Positioning System (GPS) provides highlyaccurate navigation data: position, velocity, and time reference. GPS is often aided by the INU,

AHRS, and Doppler data. GPS is accurate with four or more properly oriented satellites.Accuracy is degraded with improperly placed satellites or fewer than four satellites visible. GPS-

INS

is the most accurate of modes listed, with day/night and all weather capability.

Go around (GA).

A basic guidance mode, providing lateral guidance, longitudinal guidance and vertical guidance

to climb then to accelerate, while maintaining a wings-level roll; in some implementations (suchas SOA), individual axes can be overridden by other modes (for example, longitudinal with G/S

SEL and vertical with RALT SEL orBALT SEL)


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GPS.

Global Positioning System

GPS-DNS.

GPS using DNS

GPS-INS.

GPS using INS

Gravitational acceleration.

Acceleration caused by the force of gravity; Symbols: g; Typical Units: ft/s-squared,g;Dimensions: Length / Time-squared;

Gravity.

Force exerted by gravity; gravity sometimes includes effects of the earth's rotation; gravity isoften treated as a constant, but for greater accuracy gravity is a function of latitude, altitude, and

the phase of the moon (yes, it's true); Symbols: g; Typical Units: lbf,kip;Dimensions:Mass *Length / Time-squared;

Grid north.

Standard aviation term.

Grivation.

Symbols: nu sub g ; Typical Units: rad, deg;

Ground track angle (GTA).

Direction of ground speed vector with respect to true north; Synonyms: true track; Symbols: eta;

Typical Units: rad, deg;

Groundspeed.

The speed over the ground; earthspeed projected to a horizontal plane; Symbols: V sub g; TypicalUnits: kt,ft/s;Dimensions: Length / Time;

Groundspeed select (G/S SEL).

A basic guidance mode, providing longitudinal guidance to an operator selected groundspeed;


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G/S SEL.

Groundspeed select

GTA.

Ground track angle

Guidance.

System, usually software, that determines state errors of desired state minus current state,

typically three states: heading, altitude, and speed;

Guidance control law parameter (GCLP).

One of several parameters for the guidance control laws, generated by individual guidance

modes; See Also: altitude error scale factor, altitude integral gain, altitude integral input, altitudeintegral limit, controlled altitude, controlled speed, course cut limit, crosstrack deviation,

crosstrack deviation gain, crosstrack deviation rate, crosstrack deviation rate gain, desiredaltitude, desired speed, path integral gain, path integral limit, path integral value, reference

acceleration, reference acceleration gain, track angle error, track angle error gain, velocity errorscale factor; Reference: kilmer89.

Gyroscope (gyro).

An inertial device for measuring change of attitude (pitch rate, roll rate, and yaw rate);gyroscopes usually consist of a gimbled, rotating mass; gyroscopes are usually included in

inertial sensors, such as AHRS

and INS

; See Also: ring-laser gyro;

HDG SEL.

Heading select

Heading.

Direction on a compass that aircraft is pointed, measured with respect to true north or magnetic

north; Symbols: psi; Typical Units: rad, deg;

Heading error.

A basic output from guidance to flight director, indicating the difference between actual heading

and desired heading; Symbols: DELTA psi; Typical Units: rad, deg;

Heading select (HDG SEL).


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A basic guidance mode, providing lateral guidance to an operator selected heading (magneticheading or true heading, again, operator selectable);

Health.

Equipment status

High-pass filter (HPF).

A filter that allows frequencies above a cutoff frequency to pass while attenuating frequenciesbelow the cutoff frequency;

Hold.

To maintain some aspect(s) of aircraft state, such as heading, airspeed, altitude, pitch

Hook.

In the US Navy, a target cursor;

Hough.


Hover hold (HVR SYM).

A basic guidance mode, providing lateral guidance and longitudinal guidance to maintain an

operator selected north velocity and east velocity; if the selected velocities are zero, then aposition is held

HPF.

High-pass filter

HVR SYM.

Hover hold

Hysteresis.

A function in which the algorithm for computing output changes at defined events or thresholds,such that output follows one path as input increases and another path as input decreases;

Hysteresis can be formalized: (0) at initialization, select algorithm-0 (1).if event-1 occurs, switchto algorithm-1 (2) if event-2 occurs, switch to algorithm-2 ... (N) if event-n occurs, switch to

algorithm-n Frequently in avionics, hysteresis prevents a test from oscillating near the transitionpoint due to noise. Implementation is usually: (0) at initialization, set y = 0 (1) if x sub c + h/2 le


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x, then set y = 1 (2) if x sub c - h/2 lt x lt x sub c + h/2, then let y retain its value (3) if x le x subc - h/2, then set y = 0

IAS.

Indicated airspeed

IBC.

Ils Back Course

IBIT.

Initiated built-in-test

IDS.

Infrared Detecting Set

ILS.

Instrument Landing System

ILS approach.

To approach a runway using ILS

ILS Back Course (IBC).

Operation of ILS in which the runway is approached in reverse direction, giving only lateral

guidance; Compare: ILS Front Course;

ILS Front Course.

Operation of ILS in which the runway is approached in forward direction, giving lateral,

longitudinal, and vertical guidance; sometimes called ILSCompare: ILSBack Course;

Indicated airspeed (IAS).

Airspeed as instruments would indicate, not corrected for instrumentation errors or air density;

See Also: airspeed; Symbols: V sub 'IAS'; Typical Units: kt,ft/s;Dimensions: Length / Time;

Inertial.

Based on inertia, such as with an INS or an AHRS


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Inertial Navigation System (INS).

An Inertial Navigation System (INS) is a self-contained navigation system. It consists ofgyroscopes and accelerometers to provide attitude, heading, position, attitude, body/inertial

velocity, and acceleration information. A primary navigation data source. INS loses accuracy

with time due to drift of gyroscopes. INS

-DNS

is moderately accurate over land, not good overwater. See Also: Inertial Navigation Unit;

Inertial Navigation Unit (INU).

A self-contained Inertial Navigation System;

Infrared Detecting Set (IDS).

Forward-Looking Infrared;

Initialization.

A basic control to a data source from controls and displays for initializing a device. Initiated bypower-on, operator, driver, orMC; During initialization, the device is usually not available;

Also, a procedure to reset physical devices to a known state; Values: initialization in progress,not initialized, unreliable, normal, redundant, degraded, failed. See Also: alignment,

boresighting, calibration;

Initiated built-in-test (IBIT).

Selftests running internal to a device initiated external to the device, usually an operator, causing

the device to temporarily cease normal operation;C

ompare: periodic built-in-test;

Inner marker.

Innermost marker beacon on an ILS

INS.

Inertial Navigation System

Instrument Landing System (ILS).

Equipment determining glideslope, localizer (bearing), and distance (marker beacon) to arunway; ILS provides precision aiding for landing; ILS is usually part of a VORstation. A basic

guidance mode, providing lateral guidance, longitudinal guidance, and vertical guidance toapproach a runway for landing; in ILS back course, vertical guidance is not provided

Instrumentation.


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Hardware to measure and to monitor a system

Integrate.

To combine multiple systems; Also, to compute to integral of;

Integrator.

A function that integrates; Many types of integrators exist; in fact, they constitute entire books.

Avionics software usually relies on rectangular, single integrators, but occassional usestrapezoidal or double integrators.

International.


Interpolate.

Function to determine intermediate values from two or values in a table; usually linear but can behigher order; endpoints are either extrapolated or limited;

Interrogation.

A request of data

INTLIM.

Path integral limit

INTMAGLIM.

Altitude integral limit

INTVAL.

Path integral value

INU.

Inertial Navigation Unit

Invalid.

An indication that data from a device is bad and cannot be trusted

Jerk.


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Rate of change of acceleration, either scalar or vector, often with subscripts such as ENU orXYZ to denote the coordinate frame; time derivative of acceleration; Symbols: j,J; Typical Units:

ft/s-cubed;Dimensions: Length / Time-cubed;

Kalman filter.

A filter for combining multiple data sources, usually of different types, to produce an estimatebetter than any single source; Compare: averaging filter, complementary filter;

KALTINT.

Altitude integral gain

KINT.

Path integral gain

KLA.

Reference acceleration gain

KTAE.

Track angle error gain

KVSF.

Velocity error scale factor

KXTKD.

Crosstrack deviation gain

KXTKR.

Crosstrack deviation rate gain

KZSF.

Altitude error scale factor

Laplace transform.

A mathematical relationship to model a continuous function in the complex frequency domain

(S-plane); Laplace transforms are commonly used by systems engineers to describe avionicssystems; Compare: continuous-time equation, difference equation, differential equation,


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discrete-time equation, state-space model, Z transform; See Also: first-order filter, integrator,second-order filter, unit functions;

Laser obstacle avoidance / terrain avoidance sensor (OA/TA).

A sensor that provides warnings for long, thin objects (like wires). It has at least a 20deg x 30degFOV, which is both velocity tracked and pitch stabilized. It provides warnings (every 2.5seconds) for long, thin obstacles (like wires) at 400 meters detection range and contour flight at

80-120 knots.

Lateral.

Related to latitude; across an aircraft left to right

Lateral cue.

A cue to control heading; lateral cyclic cue See Also: wheel cue,

Lateral cyclic.

A flight control operated by moving left or right with hand in rotary-wing aircraft, primarily tocontrol roll (heading); controls differential pitch of the rotors as they rotate from one side to the

other on a rotary-wing aircraft;

Lateral cyclic cue.

A lateral flight director cue for rotary-wing aircraft, primarily to control heading, by changing

roll;C

ompare: wheel cue; Symbols: Gamma sub 'LAT'; Typical Units: percent,in;

Lateral guidance.

Calculations for the lateral axis of the appropriate guidance modes. The control law lateral axis

input data are: Cross Track Deviation, Cross Track Deviation Rate, Cross Track Deviation RateGain, Track Angle Error, Track Angle Error Gain, Course Cut Limit, Path Integral Limit, Path

Integral Gain. The major output from Longitudinal Guidance is the speed error for the selectedlongitudinal guidance mode.

Latitude.

Position on earth, north or south of the equator; See Also: astronomical latitude, geocentric

latitude, geodetic latitude; Symbols: Phi; Typical Units: rad, deg;

Leg.

A segment of a flight plan; flight path between two waypoints


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LF ADF.

Low Frequency Automatic Direction Finding

LOC.

Localizer

Lift.

Force, created primarily by wings (fixed wing) or by rotors (rotary wing), acting in opposite

direction of gravity vector; Symbols: Length; Typical Units: lbf,kip;Dimensions:Mass * Length/ Time-squared;

Limiter.

A filter that passes the input to the output, except that the output is limited to a minimum valueand a maximum value; Compare: rate limiter;

Localizer (LOC).

Part of ILS that provides lateral deviations from a preset course;

Longitude.

Position on earth, east or west of the prime meridian; Symbols: lambda; Typical Units: rad, deg;

Longitudinal.

Related to longitude; lengthwise along the center line of an aircraft forward

Longitudinal cue.

A cue to control pitch; longitudinal cyclic cue See Also: throttle cue,

Longitudinal cyclic.

A flight control operated by moving fore or aft with hand in rotary-wing aircraft, primarily to

control pitch (speed); controls differential pitch of the rotors as they rotate from nose to tail on arotary-wing aircraft;

Longitudinal cyclic cue.

A longitudinal flight director cue for rotary-wing aircraft, primarily to control speed, by

changing pitch; Compare: throttle cue; Symbols: Gamma sub 'LONG' ; Typical Units: percent,in;


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Longitudinal guidance.

Calculations for the longitudinal axis of the guidance modes. The control law longitudinal axisinput data are: Reference Acceleration, Reference Acceleration Gain, Desired Velocity, Velocity

ErrorScale Factor. The major output from Longitudinal Guidance is the speed error for the

selected longitudinal guidance mode.

Low Frequency Automatic Direction Finding (LF ADF).

Equipment that determines bearing to a radio station on a low frequency band, usually thestandard AM band;

Low-pass filter (LPF).

A filter that allows frequencies below a cutoff frequency to pass while attenuating frequencies

above the cutoff frequency; See Also: first-order filter;

LPF.

Low-pass filter

Mach number.

Ratio of airspeed to the local speed of sound (Mach 1 is the speed of sound under currentatmospheric conditions); Symbols:M;

Magnetic heading.

Heading of the aircraft relative to magnetic north; AMagnetic Heading Sensor provides this

heading data. Symbols: psi subM; Typical Units: rad, deg;

Magnetic variation (MVAR, MAGVAR).

Difference between true north and magnetic north, varying with position; magnetic variation

drifts with time; Symbols: nu; Typical Units: rad, deg;

MAGVAR.

Magnetic variation

Maintenance.

Indicates device is in a maintenance mode; Values: non-maintanance, calibration, alignment,

boresight

Map.


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Equipment that produces a map image; See Also: DigitalMap Generator

Marker beacon (MB).

Part of Instrument Landing System that signals crew members of distance to runway, consisting

of three markers:. inner, middle, and outer;

Massaged.

Filtered, estimated, or derived, or some combination of the three

Master caution.

A signal which indicates that one or more caution lights has been activated (fromMIL-STD-

1472D);

Master warning.

A signal which indicates that one or more warning lights has been activated (fromMIL-STD-1472D);

MB.

MarkerBeacon

MC.

Mission computer

Mean sea level (MSL).

Standard aviation term See Also: above sea level;

Measured.

Raw data converted to standard units; Compare: derived, estimated, filtered, raw, selected,smoothed

Meridian radius of curvature.

Radius of the earth in the east/west direction at a given position; Synonyms: earth radiusnorth/south; Symbols: rho subM; Typical Units: ft;Dimensions: Length;

Middle marker.

Marker beacon located where the center of the glideslope is 200ft above the runway


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Mission computer (MC).

Mission processor;

Mission objectives.

Goals to be accomplished during a specific mission, including flight plan, NRPs, legs, and a plan

on how to accomplish these objectives; plan includes, usually on a leg-by-leg basis, navigationmodes, radio navigation modes, guidance modes, flight director modes, data source control

information such as frequencies; See Also: capture criterion

Mission processor (MP).

A general purpose computer to host avionics software. Synonyms: mission computer;

MLS.

Microwave Landing System

Mode.

A selection of one of several alternatives, such as guidance mode (VOR, TACAN, or Waypoint),or navigation mode (INS, Doppler, or dead reckoning)

Modified Everest.


Moding cursor.

A symbol on a display, moved by an operator much like arrow keys for menu selection, to selectone of several options

MP.

Mission processor

MSL.

Mean sea level

Multi-mode radar (MMR).

AMulti-Mode Radar is used for Terrain Following (TF) and Terrain Avoidance (TA), Ground

Mapping (GM) and Air-to Ground Ranging (AGR). The TF mode supplies commands which areprocessed and displayed as climb/dive commands on the Flight Director display and E-squared


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video used by the operators in anticipating near term TF commands. When in TA or GM modes,the operator is provided with a Plan Position Indicator (PPI) display. The AGRmode allows the

operators to determine the range to a designated target, which can be used for position updates.

MVAR.

Magnetic variation

Nacelle.

An enclosure on an aircraft.

Nap-of-the-earth flight.

Flight with a goal to remain close to the earth, usually below the height of surrounding trees andless than 100 ft above the terrain; Compare: terrain following

Natural frequency.

Standard engineering term See Also: second-order filter; Symbols: omega sub n; Typical Units:

rad/s,Hz;Dimensions: 1/Time;

Navigation.

A system, usually software, in which the primary purpose is to generate position relative to a

coordinate frame, usually fixed earth frame, such as latitude and longitude or UTM;

Navigation aid.

A device or process to help with navigation, such as a VORstation or a position update;

Navigation reference point (NRP).

A point, usually fixed in earth coordinates but possibly moving; Also, a basic guidance mode,

providing lateral guidance to an NRP, either by course or by direct (operator selectable);Synonyms: point;

Noise.

Part of received data that is undesired, consisting of random sinusoidal terms added to a signal;Compare: offset, signal;

Normalizer.


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Function to restrict input to a specific range, such as restricting an angle alpha in radians so that -pi le alpha le +pi; angles usually require normalizing following any computation; normalized

variables often present problems for filters and other functions at their discontinuities;

NRP.

Navigation reference point

OA.

Obstacle avoidance

OAT.

Outside Air Temperature

Obstacle avoidance (OA).

Flight cues designed to avoid obstacles, such as terrain, buildings, and power lines; Compare:terrain avoidance, threat avoidance;

Off.

Device is powered off (power switch is off; no response to communications) - no data andfunction is available.

Offset.

Part of received data that is undesired, consisting of a random, time-invariant term added to asignal; Synonyms: bias; Compare: noise, signal

OMEGA.

An OMEGA receiver provides position information that can be used to update the aircraft

navigation position. OMEGA is the least accurate method of obtaining position information.

Operations.

How well is equipment operating;V

alues: operational (all function and data is available),degraded (equipment has partially failed with some function or data unavailable and someavailable), failed (equipment has failed with no function or data available);

Orientation.

Direction in reference to a coordinate frame


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Outer marker.

Marker beacon located 5-7mi from the end of the runway; See Also: marker beacon

Outside Air Temperature (OAT).

The temperature just outside the aircraft; Symbols: T; Typical Units: deg;Dimensions:

Temperature

Override.

To alter selection made automatically by software

Past status words.

Status words that are logically combined over time (such as ``and''ing or ``or''ing) to provide

history of what has been set in the past

Path integral gain (KINT).

A guidance control law parameter, generated by the lateral guidance modes;

Path integral limit (INTLIM).

A guidance control law parameter, generated by the lateral guidance modes; Typical Units: rad;

Path integral value (INTVAL).

A guidance control law parameter, generated by the lateral guidance modes; Typical Units: ft;Dimensions: Length

PBIT.

Periodic built-in-test

Pedal.

A flight control operated by pushing with feet, primarily to control yaw via the rudder in fixed-

wing aircraft or thrust to tail rotor in rotary-wing aircraft; pedals are automatically controlled inmodern aircraft;

Period.

Time of a periodic process; 1/f where f is the sampling frequency; Symbols: T; Typical Units: s;

Dimensions: Time.


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Periodic.

A process that executes at a fixed rate; Compare: aperiodic;

Periodic built-in-test (PBIT).

Selftests running internal to a device as part of normal operation; Compare: initiated built-in-

test;

Personnel Locating System (PLS).

A basic guidance mode, providing lateral guidance to a PLS transmitter from range and bearinginputs. Equipment that determines range and bearing to a personnel with a PLS transmitter;

Provides range and bearing to locate ground personnel. Coded continuous or periodicinterrogations of the portable ground radios are used to provide the information.

PFCS.

Primary flight control system

Physical device.

A piece of equipment, a subsystem; Synonyms: device

Piloted simulation.

Real-time engineering simulation

Pitot pressure.

Total pressure

Pitch.

The angle of a rotor measured in the plane of rotation; Symbols: theta,Theta; Typical Units: rad,

deg;

Pitch cue.

Flight director cue to control pitch; in fixed-wing aircraft, a yoke cue; in rotary-wing aircraft, alongitudinal cyclic cue

Pitch rate.

Rate of change of pitch; time derivative of pitch; Symbols: p; Symbols: theta dot; Typical Units:rad/s,deg/s;Dimensions: 1/Time;


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PLS.

Personnel Locating System

Position.

Location, usually in fixed earth coordinates such latitude and longitude; location, either scalar or

vector, often with subscripts such as ENU or XYZ to denote source or coordinate frame; timeintegral of velocity; Symbols: p,P,x,y,z; Typical Units: ft,nmi;Dimensions: Length;

Position update.

To cause navigation sensors, devices, or algorithms to reset position to value known to be more

accurate due to inaccuracies and drift in the devices and algorithms

Precision.

Measure of exactness, possibly expressed in number of digits, for example, computed to the

nearest millimeter; Compare: accuracy

Present status words.

Most recently reported status words

Pressure.

Barometric pressure

Pressure altitude.

Barometric altitude

Primary flight control system (PFCS).

The most basic part of the flight controls operated by a pilot, including wheel (fixed wing), yoke

(fixed wing), cyclic (rotary wing), pedals (fixed wing and rotary wing), throttle (fixed wing), andcollective (rotary wing);

Primary units.

A standard set of four units to which all units can be resolved; primary units areMass(M),

Length(L), Time(theta), and Temperature(T); for example, standard units for velocity might bekt (nmi/hr), ft/s, m/s, mph, but primary are always Length / Theta; sometimes written with

negative subscripts.

Prime radius of curvature.


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Radius of the earth in the east/west direction at a given position; Synonyms: earth radiuseast/west; Symbols: rho sub P; Typical Units: ft;Dimensions: Length;

Quaternion.

A system of representing attitude by measuring angle of aircraft center line with respect to threeorthoginal axes plus rotation about centerline; quaternions are used over Euler angles (pitch, roll,yaw) when pitch can approach 90deg because of a singularity on Euler angles at 90deg; discrete-

time computations using quaternions can run more slowly than those with Euler angles whileproducing results of the same accuracy See Also: Euler parameters;

RADALT.

Radar Altimeter.

Radar altimeter (RADALT).

Measures height above terrain. The altitude is monitored to provide a low altitude warning

during TF operations and landing operations. It can also be used as input to the TerrainReference Navigation algorithm for position updates.

Radar altitude.

Height with respect to the terrain below (distance above closest dirt); Synonyms: above ground

level; Symbols: h sub r; Typical Units: ft;Dimensions: Length;

Radar altitude select (RALT SEL).

A basic guidance mode, providing vertical guidance to an operator selected radar altitude;

Radial error probability (REP).

A probability that a percentage of one-dimension measurements will lie on a radial (line) ofgiven length, with the origin centered at truth or mean of the measurements; used to specify test

cases for measurement errors of sensors of one dimension, such as vertical velocity; Compare:circular error probability, spherical error probability;

Radio navigation.

Navigation relative to radio station, providing, for example, of relative bearing, range, lateral

deviation, and glideslope; Examples include VOR, TACAN, and PLS. Radio navigation differsfrom other navigation in that the transmitter signals often dropout for a long period of time, like

minutes. This can occur because of natural obstructions, or because the transmitter was shutdown intentionally. In hostile territory, a PLS can locate a downed pilot, who would be foolhardy

to be continuously transmitting, but would transmit infrequently with small bursts of data. TheRadio- Navigation system accommodates this phenomenon by simulating range and bearing to


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the fixed site when it is not transmitting. After reacquiring a mobile transmitter, the mobilestation's position is re-determined. The navigation component supports wash-out filters on output

data.

RALT SEL.

Radar altitude select

Range (rng).

Standard aviation term Synonyms: distance; Symbols: r; Typical Units: ft,nmi - method of

measurement dependent on use;Dimensions: Length;

Ranging.

Act of determining a range

Rate limiter.

A filter that passes the input as the output, except that rate of change of the output is limited to a

maximum absolute value; Compare: limiter;

Raw.

Data taken directly from the sensor; Compare: derived, estimated, filtered, measured, selected,

smoothed

Real time.

Time in a computational process which runs at the same rate as a physical process; for example,

algorithms designed to run a fixed period t (filter time constants at set for t) and actually executewith frequency 1/t execute in real time; Avionics systems must run in real time;

Real-time engineering simulation (rtes).

A simulator designed to test avionics algorithms with a pilot in the loop, consisting of a

simulated cockpit, an aircraft model, sensor models, and algorithms to be tested; rtes is oftenused during development to check algorithms, such as the navigation, radio navigation, guidance

and flight director, prior to full-scale software development; rtes gives systems engineers earlyinsight in human factors problems, pilot complaints, algorithm bugs, unstability in the

algorithms, expected performance (accuracy), and pilot-machine interaction; Synonyms: pilotedsimulation; Compare: built-in simulation;

Reasonableness.


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A test to determine if data is reasonable, for example, radar altitude must be positive, and twodevices should return similar data within known limits of each other

Receive.

To absorb rf energy

REFACC.

Reference acceleration

Reference.

What must be achieved in order to match a plan; Synonyms: desired;

Reference acceleration (REFACC).

A guidance control law parameter, generated by the longitudinal guidance modes; Typical Units:

ft/s-squared, g;Dimensions: Length / Time-squared

Reference acceleration gain (KLA).

A guidance control law parameter, generated by the longitudinal guidance modes; Typical Units:

s;Dimensions: Time.

Reject.

To disallow a position update, usually by an operator;C

ompare: accept

Relative.

Applies to measurements, in a non-standard, moving reference, as opposed to fixed reference;

Compare: absolute;

Relative bearing.

Angle from aircraft center line to bearing of the destination; Symbols:B sub R; Typical Units:

rad, deg;

Remote terminal (RT).

Term defining role of a device on aMIL-STD-1553 bus as being a slave; Compare: bus

controller;

Remote Terminal Unit.


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Signal Data Converter;

Rendezvous.

To meet with another aircraft in the air, for refueling or other mission objectives

Rendezvous approach.

To approach a planned rendezvous point

REP.

Radial error probability

Reported.

Data from a device

Ring-laser gyro (RLG).

A gyroscope based on a laser beam instead of a rotating mass, providing to same data as a

gyroscope;

RLG.

Ring-laser gyro

RMS.

Root mean square;

RNG.

Range

Roll.

Bank angle; Symbols: phi,Phi; Typical Units: rad, deg;

Roll cue.

Flight director cue to control roll; in fixed-wing aircraft, a wheel cue; in rotary-wing aircraft, a

lateral cyclic cue

Roll rate.


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Rate of change of roll; time derivative of roll; Symbols: q; Symbols: phi dot; Typical Units:rad/s,deg/s;Dimensions: 1/Time;

Root mean square (RMS).

A statistical measure of data; the root of the mean of the square; for variables with mean of zero,the standard deviation is equal to the rms; Compare: root sum square;

Root sum square (RSS).

A statistical measure of data; the root of the sum of the square; for a vector, its length is equal to

the rss of its scalar elements; Compare: root mean square;

Rotary wing.

A helicopter;

RSS.

Root sum square;

RT.

Remote terminal

RTES.

Real-time engineering simulation

RTU.

Remote Terminal Unit

Rudder.

A control surface on fixed-wing aircraft, usually mounted at aft end of the fuselage sticking up(like a dorsal fin), that controls yaw (heading), and is controlled by the pedals; Symbols: delta

sub R; Typical Units: rad, deg;

S-plane.

Continuous complex frequency plane; S-plane is used in control systems engineering in the

design of control laws See Also: Laplace transform;

Sampling frequency.


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Rate of a periodic process; 1/T where T is the period; Symbols: f sub s; Typical Units: Hz;Dimensions: 1/Time.

SDC.

Signal Data Converter

Search pattern.

Basic guidance mode; provides lateral steering guidance to fly an expanding square searchpattern, creeping line search pattern, or sector search pattern.

Second-order filter.

A smoothing filter in which the output follows the input, only more slowly; It is usuallyimplemented in software as a difference equation of period T. When the second-order filter is

used in avionics, it is commonly to smooth data, and to wash out transients at mode change.Usually, a first-order filter suffices, and it being less expensive, is chosen over a second-order

filter. Typical values for omega sub n, a, and b are 0.1-2 rad/s, and zeta 0.1-0.9. It should also benoted that two first-order filters can be chained together to form a second-order filter that is

critically damped or overdamped. When implementing a second-order filter on normalizedvariables, such as angles, the discontinuities require special treatment.

Sector search.

A pattern of concentric arcs followed for searching the ground from an aircraft; Compare:

creeping line search, expanding square search;

Selected.

Measured data picked from one of many sensors; Selecting is the process of choosing the "best"

parameter from multiple copies of that parameter, from multiple, identical devices or similardevices. Compare: derived, estimated, filtered, measured, raw, smoothed

Selftest.

A test internal to a device

Semi-circle.

A measure of angle, 1 semi-circle = pi rad = 180 deg; angles from physical devices are oftenreported in semi-circles in order to compress data

Sensor.


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A device that measures, receives, or generates data, for example, an INS, a FLIR, a map. SeeAlso: Data Source Object

Sensor Fusion/Correlation (SFC).

Measure of convergence of sensor data

SEP.

Spherical error probability

SFC.

Sensor Fusion/Correlation

Shutdown.

To cease normal operations

Sideslip angle.

Symbols: beta; Typical Units: rad, deg;

Signal.

Part of received data that is desired; Compare: noise, offset

Signal Data Converter (SDC).

A device that converts unique signals to a standard protocol, usuallyMIL-STD-1553B;

Synonyms:Remote Terminal Unit;

Signal-to-noise ratio (SNR,S/N).

A ratio of magnitude of a desired signal to the magnitude of the noise received with it; Typical

Units: dB;

Situational awareness.

Situational awareness provides the pilots with information relative to the current surroundings,

such as other aircraft or threats in the immediate area.

Slant range.

Direct line distance, not along the ground;


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Slats.

A control surface on fixed-wing aircraft, usually mounted to the aft edge of the wings, thatextends the wing to provide added lift at low speeds; Compare: flaps; Symbols: delta sub S;

Typical Units: rad, deg;

Smoothed.

Data that is the result of conditioning a signal with a simple filter; Compare: derived, estimated,

filtered, measured, raw, selected; smoothing is usually less sophisticated than filtering

Smoothing filter.

A filter to reduce quick changes of a signal by attenuating high frequencies; See Also: first-orderfilter, second-order filter, wash-out filter;

S/N.

Signal-to-noise ratio

SNR.

Signal-to-noise ratio

South American.


Speed.

Scalar velocity;

Speed cue.

Flight director cue to control speed; in fixed-wing aircraft, a throttle cue; in rotary-wing aircraft,

a longitudinal cyclic cue

Speed error.

A basic output from guidance to flight director, indicating the difference between actual speedand desired speed; Symbols: DELTA V; Typical Units: ft/s,kt;Dimensions: Length / Time.

Spherical error probability (SEP).

A probability that a percentage of three-dimension measurements will lie within a sphere ofgiven radius, with the sphere centered at truth or mean of the measurements; SEP specifies test


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cases for measurement errors of sensors of three dimensions, such as velocity east, north, andvertical. Compare: circular error probability, radial error probability;

Spoiler.

A control surface on fixed-wing aircraft, usually mounted to the wings, that provides roll controland lift; Symbols: delta sub S; Typical Units: rad, deg;

Stability coordinates.

Coordinates referenced to the air mass; Compare: body coordinates, earth coordinates;

Stabilizer.

A control surface, usually mounted at aft end of the fuselage parallel to the wings, that providespitch stability, some aircraft have an adjustable stabilizer; Symbols: delta sub H; Typical Units:

rad, deg;

Stagnation pressure.

Total pressure

Standard units.

Units commonly encountered for a particular quantity;

State data.

Data that defines aircraft parameters, such as position, velocity, attitude; Some standard terms forstate data include: Groundspeed vector, wind speed vector, true airspeed vector, true bearing,

true track, ground track angle, relative bearing, sideslip angle, drift angle, true heading, magneticvariation, grivation. earthspeed vector, vertical velocity, air mass flight path angle, earth-

referenced flight path angle, angle of attack, pitch, radar altitude, barometric altitude, earthradius, glideslope, gravity vector, lift vector, lateral acceleration vector, bank angle.

State-space model.

A mathematical relationship of a system in time using state variables, inputs, outputs, and

constants; The state-space model is composed of n state variables (x sub 1 , x sub 2 , ..., x sub n),m input variables (u sub 1 , u sub 2 , ..., u sub m), k output variables (y sub 1 , y sub 2 , ..., y sub

k), and four constants a, b, c, and d. Alternatively, a state-space model can be expressed withmatrices. Compare: continuous-time equation, difference equation, differential equation,

discrete-time equation, Laplace transform, Z transform;

Static pressure.


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A measure of barometric pressure as if the sensor were not moving with respect to the air;Compare: total pressure; Symbols: p sub s; Typical Units: psi,lbf/in-squared;Dimensions:Mass

/Time-squared * Length

Station.

A structure on the ground, perhaps containing VORor TACAN

Status.

An indicator of how well a system or subsystem is working

Status indicator.

An binary indicator of a particular aspect of a device; status indicators are independent of eachother; status indicators listed in this dictionary are derived from existing programs. See Also: off,

warning, operations, communications, useability, initialization, test, maintenance, unknown;

Status words.

Data words reported by devices to indicate status; Each bit is defined on a device-by-devicebasis. The number of words vary from device to device. Status words are used by maintenance

personnel and maintenance software. Present, past, and test status words are reported.

Strapdown inertial sensor.

Accelerometers mounted to a platform fixed to the aircaft; Compare: gimbaled inertial sensor

Surface.

Related to surface of water;

Surface Wind Wave Motion (SWWM).

..

Survivability.

A survivability subsytem detects and counters hostile actions.

Swashplate.

A device to control the pitch of rotors; on rotary-wing aircraft, the swashplate is controlled by acollective and a cyclic;

SWWM.


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Surface Wind Wave Motion

System.

Applied to measurements, means the best value that the system can determine.

TA.

Terrain avoidance

TACAN.

Tactical Air Navigation;

TACAN Point-to-Point (TCNP).

A basic guidance mode, providing lateral guidance to a point relative to a TACAN station byspecified range and bearing;

Tachometer.

A device for measuring angular velocity;

Tactical Air Navigation (TACAN).

A basic guidance mode, providing lateral guidance to a TACAN station; Equipment that

determines range and bearing to a radio station with a TACAN transmitter;

TAE.

Track angle error

Target.

Object or point pointed by FLIRor radar

Target cursor.

A symbol on a display, moved by a track handle or similar device, to select objects on thedisplay

TAS.

True airspeed

Taut line.


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Basic guidance mode; provides vertical guidance to maintain a taut line for a dipping sonar, orother such device.

TCN.

Tacan

TCNP.

Tacan Point-to-Point

Terrain.

The contour of the earth;

Terrain avoidance (TA).

Flight such that the aircraft maintains a constant barometric altitude but flies around obstacles;

Compare: obstacle avoidance, threat avoidance;

Terrain following (TF).

A basic guidance mode, providing vertical guidance to maintain an operator selected radar

altitude above the terrain. Flight such that the aircraft tries to maintain a constant height abovethe terrain, usually in the range of 100-1,000 ft; Uses a g-command from theMulti-Mode Radar

to generate a flight director cue. This controls the aircraft flight path so that the set clearancealtitude is achieved over major high points in the terrain with zero flight path angle. Compare:

nap-of-the-earth flight;

Terrain Referenced Navigation (TRN).

A navigation mode based on comparison of barometric altitude and radar altitude with a map;

Kalman filters correlate the terrain data and the altitudes. A primary navigation data source. TRNcombines INS with map references. It is most accurate over rough terrain. Does not give accurate

data while over flat areas or water. See Also: DigitalMap Generator;

Test status words.

Status words reported at the conclusion of a test.

Values: test in progress, not tested, normal,redundant, degraded, failed;

TF.

Terrain following;

ThA.


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Threat avoidance

Threat avoidance (ThA).

Flight cues designed to avoid enemy threats, such as anti-aircraft artillery and aircraft; Compare:

obstacle avoidance, terrain avoidance;

Throttle.

A flight control operated by moving fore or aft with hands, primarily to control thrust (speed) infixed-wing aircraft;

Throttle cue.

A longitudinal flight director cue for fixed-wing aircraft, primarily to control speed, by changingpower; Compare: longitudinal cyclic cue; Symbols: Gamma sub LONG; Typical Units:

percent,in;

Thrust.

Force, created by engines and rotors, acting in the direction of the engine; Symbols: T; TypicalUnits: lbf,kip;Dimensions:Mass * Length / Time-squared;

Tilt rotor.

An aircraft with tilting rotors for fixed-wing flight or rotary-wing flight;

Time constant.

Constant for a first-order filter determining time at which the output of the filter reaches nearly

0.6321 percent of a step input; Symbols: tau; Typical Units: s;Dimensions: Time;

Tolerances.

Allowed error in measurements

Total pressure.

A measure of barometric pressure in the moving air; Synonyms: dynamic pressure, Pitotpressure, stagnation pressure; Compare: static pressure; Symbols: p sub t; Typical Units:psi,lbf/in-squared;Dimensions:Mass /Time-squared * Length

Track (TRK).

A basic guidance mode, providing lateral guidance to an operator selected ground track;


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Track angle error (TAE).

A guidance control law parameter, generated by the lateral guidance modes; Typical Units: rad;

Track angle error gain (KTAE).

A guidance control law parameter, generated by the lateral guidance modes;

Track handle.

A device to move a cursor in two axes on a display, much like a mouse

Tracking.

Tracking is performed by the TRN

Transceivers.

A device that receives and transmits

Transient-free switch.

A switch with a wash-out filter so that the output contains no transients (steps) at switch time

Transmit.

To radiate RF energy

Transmitter.

A device that transmits

Trim tab.

A secondary control surface, usually mounted to primary control surface such as aileron,

elevator, rudder, or stabilizer, that controls the position of the primary control surface, and iscontrolled by the an operator or an autopilot; Symbols: delta sub T; Typical Units: rad, deg;

TRK.

Track

TRN.

Terrain Referenced Navigation;


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TRN-INS.

TRN with INS

True.

Best available estimate, such as true airspeed; referenced to true north, such as true heading;

True airspeed (TAS).

Airspeed corrected for instrumentation errors and air density; See Also: airspeed; Symbols: V sub

'TAS'; Typical Units: kt,ft/s;Dimensions: Length / Time;

True bearing.

Symbols:B sub T; Typical Units: rad, deg;

True heading.

Heading of the aircraft relative to true north; Symbols: psi sub T; Typical Units: rad, deg;

True track.

Ground track angle; Symbols: T sub T; Typical Units: rad, deg;

Tune.

To set the operating frequency or channel for a device

UHF/VHF Automatic Direction Finding (U/V ADF).

An Automatic Direction Finder that determines relative bearing to a transmitter to which it istuned, in either the UHF band or VHF band;

Unit functions.

A collection of functions used as standard test cases in control systems engineering; The primary

unit functions of interest in avionics are the unit impulse, the unit step, and the unit ramp.

Symbols: u sub k ( t );

Unit impulse.

A function used as a standard test case in control systems engineering; a spike of ``area'' one attime t = 0; Synonyms: impulse; See Also: unit functions; Symbols: u sub ( t ), delta ( t );

Unit ramp.


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A function used as a standard test case in control systems engineering; a line of slope 1 startingat zero at time t = 0; Synonyms: ramp; See Also: unit functions; Symbols: u sub < -2> ( t );

Unit step.

A function used as a standard test case in control systems engineering; a step from zero to one attime t = 0; Synonyms: step; See Also: unit functions; Symbols: u sub< -1>( t ), u( t );

Unitless.

No units, such as ratios; a quantity with standard units of 1; a quantity with primary units of 1;

Synonyms: dimensionless;

Units.

A standard quantity, such as ft or mi; Synonyms: dimension;

Universal Transverse Mercator (UTM).

A system of fixed earth coordinates, sometimes used instead of latitude and longitude, accurate

relative to others close by, such as ground troops;

Update.

A process by which position is reset with a known better position; updates occur at the data

source level or at the physical device level, depending upon specific implementation of thedevice and the data source (choice of implementation is transparent above the data source); all

updates are operator initiated, but the new position may be derived from other sources such asFLIR, MMR, or radio navigation; a basic control to a data source from controls and displays for

updating a device Compare: aiding;

UTM.

Universal TransverseMercator

U/V ADF.

UHF/VHF Automatic Direction Finding

Velocity.

Rate of change of location, either scalar or vector, often with subscripts such as ENU or XYZ todenote the coordinate frame; time derivative of position; time integral of acceleration; Symbols:

v,V; Typical Units: kt,ft/s;Dimensions: Length / Time;

Velocity east.


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Aircraft velocity in true east direction; Symbols: V sub E; Typical Units: kt, ft/s;Dimensions:Length / Time;

Velocity error scale factor (KVSF).

A guidance control law parameter, generated by the longitudinal guidance modes;

Velocity north.

Aircraft velocity in true north direction; Symbols: V sub N; Typical Units: kt,ft/s;Dimensions:Length / Time;

VERT SPD.

Vertical speed hold

Vertical.

Reference to earth radial, for example, vertical velocity is velocity along earth radial; See Also:East-North-Vertical;

Vertical acceleration.

Aircraft acceleration in earth vertical direction; Symbols: A sub V; Typical Units: ft/s-squared,g;Dimensions: Length / Time-squared;

Vertical cue.

A cue to control altitude; See Also: yoke cue, collective cue;

Vertical guidance.

Calculations for the vertical axis, rather than the longitudinal axis. The control law vertical axisinput data are: Desired Altitude, Altitude Integral, Altitude Integral Gain, Altitude Integral Limit,

Altitude ErrorScale Factor,Magnitude limit for delta altitudes. The major output from VerticalGuidance is the altitude error for the selected vertical guidance mode.

Vertical speed hold (VERT SPD).

A basic guidance mode, providing vertical guidance to maintain an operator selected verticalspeed;

Vertical velocity.

Aircraft velocity in earth vertical direction; Symbols: V sub V; Typical Units: ft/s;Dimensions:Length / Time;


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VHF Omnirange (VOR).

Equipment that determines bearing to a radio station with a VOR transmitter; VOR transmittersusually contain ILS transmitters in addition to VOR; A basic guidance mode, providing lateral

guidance to a VORstation. A VOR/ILS/MB. radio receiver provides a VHF Omni-DirectionR

ange (VOR

) function and Instrument LandingS

ystem withM

arkerB

eacon (MB

) function.VORprovides beari

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Aviation Terminology