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Distance of the aircraft above the
ground *Synonyms:* radar altitude;

Distance of the aircraft above mean sea
level

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

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;

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

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

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;

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

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

To begin reception of useful data

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; *See Also:* capture criterion; *Compare:* arm,
capture;

Air data computer

Air data dead reckoning

Automatic Direction Finding

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);

Automatic flight control system

Above ground level

Air-ground ranging

Straight-line distance from the aircraft to a
point on the ground;

Approach to hover

Attitude Heading Reference System

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;

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;

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.

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

Straight-line distance from the
aircraft to a point on the ground;

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;

Standard aviation term

A craft that flies in the air; either fixed or
rotory wing.

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

A standard model for computing earth data

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;

Altitude integral input

A device to measure altitude, either barometric
altitude or radar 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;

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

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

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;

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;

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

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;

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;

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;

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;

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

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

Approach

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;

Hover approach of a rotary
wing aircraft.

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;

Above sea level

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

Air Traffic Control

Environmental data related to the atmosphere
at some point of interest

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

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;

A standard model for computing earth data

A basic guidance mode,
providing lateral guidance to a radio station. Equipment that
determines bearing to a radio station;

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

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;

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;

Avionics monitor

One direction in an orthogonal reference frame;

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

Barometric altitude select

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 the composition of a low-pass filter and a high-pass filter;

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;

Height with respect to fixed earth
reference (above mean sea level); *Synonyms:* pressure altitude;
*Symbols:* h sub b; *Typical Units:* ft; *Dimensions:*
Length;

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

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:* Mass /Time-squared * Length;

Bus controller

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

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

A standard model for computing earth data

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

Built-in simulation

The aircraft, usually referring to a coordinate system;

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

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

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 they
provide 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 in correction factors to be
downloaded from the host processor to the device; during boresighting,
the device is usually not available; *See Also:* alignment,
calibration, initialization;

Band-pass filter

Bearing

Function in avionics software that
simulates sensors, aircraft, and pilot, to exercise avionics software
(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 or patches; BIS is
seldom used by aircraft flight crews or maintenance crews; *Compare:* real-time engineering simulation;

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

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;

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;

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

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

A test case to determine if an armed
objective has been captured; In avionics, an aircraft might have 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. The radial 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 can have multiple criteria.
Capture criterion are often used with radio navigation to determine a
transition from armed to active.

Calibrated airspeed

A signal which alerts the operator to an impending
dangerous condition requiring attention, but not necessarily immediate
action (from MIL-STD-1472D); an annunciator that is more critical than
an advisory but less critical than a warning;

Course cut limit

Standard aviation term

Circular error probability

A number that maps to a frequency;

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 error probability, spherical error
probability; CEP specifies test cases for measurement errors of
sensors of two dimensions, such as velocity east and north.

A standard model for computing earth data

A standard model for computing earth data

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

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

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

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

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 different types, by adding filtered values, where
the sum of the filters in the frequency domain is unity; a Kalman
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 the LFP 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;

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

Time which can have any point expressed as a
real quantity, without regard for any specific interval or processing
rate; *Compare:* discrete time;

A mathematical relationship to
describe a function of time, expressed in terms of continuous time;
*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;

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

An airfoil attached to an aircraft that is
moved to control the attitude of the aircraft; an surface to control
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;

A guidance control law parameter,
generated by the vertical guidance modes; altitude that is being
controlled *Typical Units:* ft; *Dimensions:* Length;

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

Tangential acceleration caused by
motion on a radial on a rotating surface, in aviation, it is
acceleration 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;

Measured pressure altitude corrected for
instrumentation errors

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

Towards a point at a specified course; *Compare:*
direct

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

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

Perpendicular to the course;

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

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

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

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;

Controlled altitude

Controlled speed

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

*See:* moding cursor, target cursor

The frequency at which the gain of a filter
is at an edge of a band, usually taken to be when gain is 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;

*See:* longitudinal cyclic, lateral cyclic;

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;

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

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 particular device;

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

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;

Difference; error.

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;

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

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

Desired altitude

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

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

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

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

Desired speed

Difference from desired;

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

Digitized Feature Analysis Data

Depart from hover

Distance Measuring Equipment

A mathematical relationship to model a
discrete function, expressed in terms of other values in the 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;

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. In avionics, a differential equation usually models
continuous-time phenomenon in terms of time derivatives; *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

Digitial equipment that produces
map video, and sometimes contains TRN; uses Digital Terrain Elevation
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 Terrain Referenced Navigation algorithm
correlates altitude readings with digital map data to provide position
data.

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

On a digitial map,
data for cultural features such as buildings and roads; DFAD is
usually provided by Defense Mapping Agency; *Compare:* Digital
Terrain Elevation Data;

No units, such as ratios; *Synonyms:*
unitless;

Towards a point along the shortest distance; *Compare:* course

bearing.

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

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;

Method of measurement dependent on use; *Synonyms:* range;

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

Digital Map Generator

Doppler Navigation System

A technique for measuring velocity by radiating and
determining frequency shift

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

Doppler navigation system

Dead reckoning

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;

Slow, monotonic change in measured data

Data source object

Digital Terrain Elevation Data

Data Transfer System

Total pressure

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

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

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

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.

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;

Gaussian radius of
curvature

Prime radius of curvature

Meridian radius of
curvature

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

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:* state data; *Symbols:* V sub E; *Typical Units:*
kt,ft/s; *Dimensions:* Length / Time;

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-up.

Earth Centered Inertial

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

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;

East-north-up

East-north-vertical

Atmospheric data and earth data

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

Difference between desired and measured data; *Synonyms:* delta;

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

Pitch, roll, and yaw

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

A standard model for computing earth data

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

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;

Flight control system

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;

Data that is the result of filtering a signal;
filtering is usually more sophisticated than smoothing *Compare:*
derived, estimated, measured, raw, selected, smoothed;

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 avionics to 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, the
discontinuities require special treatment.

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

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

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;

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

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;

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

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;

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

Forward-Looking Infrared

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

A position update by flying directly over a known
point

Sensor equipment used to
supplement AGR, extend the aircraft visual search capability and
provide position information for guidance and navigation update
capability. Imagery derived from the FLIR sensor is displayed in
the cockpit. FLIR pointing can be controlled manually using a
tracking handle or automatically by the Mission Computer. FLIR
converts a heat image into a video image and determines azimuth,
elevation, and sometimes range of a point; *Synonyms:* Infrared
Detecting Set;

Flight path angle

Go around

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;

Guidance control law parameter

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

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

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;

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

A navigation sensor based on
satellites; A Global Positioning System (GPS) provides highly accurate
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.

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 (such as SOA), individual axes can be overridden by
other modes (for example, longitudinal with G/S SEL and vertical with
RALT SEL or BALT SEL)

Global Positioning System

GPS using DNS

GPS using INS

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

Force exerted by gravity; gravity sometimes includes
effects of the earth's rotation; gravity is often 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;

Standard aviation term.

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

Direction of ground speed vector
with respect to true north; *Synonyms:* true track; *Symbols:*
eta; *Typical Units:* rad, deg;

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

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

Groundspeed select

Ground track angle

System, usually software, that determines state
errors of desired state minus current state, typically three states:
heading, altitude, and speed;

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, altitude integral limit,
controlled altitude, controlled speed, course cut limit, crosstrack
deviation, crosstrack deviation gain, crosstrack deviation rate,
crosstrack deviation rate gain, desired altitude, desired speed, path
integral gain, path integral limit, path integral value, reference
acceleration, reference acceleration gain, track angle error, track
angle error gain, velocity error scale factor; Reference: kilmer89.

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;

Heading select

Direction on a compass that aircraft is pointed,
measured with respect to true north or magnetic north; *Symbols:*
psi; *Typical Units:* rad, deg;

A basic output from guidance to flight
director, indicating the difference between actual heading and desired
heading; *Symbols:* DELTA psi; *Typical Units:* rad, deg;

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

Equipment status

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

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

In the US Navy, a target cursor;

A standard model for computing earth data

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 a position is held

High-pass filter

Hover hold

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, switch to 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 transition point due to noise.
Implementation is usually: (0) at initialization, set y = 0 (1) if x
sub c + h/2 le 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 sub c - h/2, then set
y = 0

Indicated airspeed

Ils Back Course

Initiated built-in-test

Infrared Detecting Set

Instrument Landing System

To approach a runway using ILS

Operation of ILS in which the runway is
approached in reverse direction, giving only lateral guidance; *Compare:* ILS Front Course;

Operation of ILS in which the runway is
approached in forward direction, giving lateral, longitudinal, and
vertical guidance; sometimes called ILS *Compare:* ILS Back
Course;

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;

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

An Inertial Navigation
System (INS) is a self-contained navigation system. It consists of
gyroscopes 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 over water. *See Also:* Inertial Navigation Unit;

A self-contained Inertial
Navigation System;

Forward-Looking Infrared;

A basic control to a data source from controls
and displays for initializing a device. Initiated by power-on,
operator, driver, or MC; 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;

Selftests running internal to
a device initiated external to the device, usually an operator,
causing the device to temporarily cease normal operation; *Compare:* periodic built-in-test;

Innermost marker beacon on an ILS

Inertial Navigation System

Equipment determining
glideslope, localizer (bearing), and distance (marker beacon) to a
runway; ILS provides precision aiding for landing; ILS is usually part
of a VOR station. A basic guidance mode, providing lateral guidance,
longitudinal guidance, and vertical guidance to approach a runway for
landing; in ILS back course, vertical guidance is not provided

Hardware to measure and to monitor a system

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

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 uses trapezoidal or double integrators.

A standard model for computing earth data

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

A request of data

Path integral limit

Altitude integral limit

Path integral value

Inertial Navigation Unit

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

Rate of change of acceleration, either scalar or vector,
often with subscripts such as ENU or XYZ to denote the coordinate
frame; time derivative of acceleration; *Symbols:* j,J; *Typical Units:* ft/s-cubed; *Dimensions:* Length / Time-cubed;

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

Altitude integral gain

Path integral gain

Reference acceleration gain

Track angle error gain

Velocity error scale factor

Crosstrack deviation gain

Crosstrack deviation rate gain

Altitude error scale factor

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 avionics
systems; *Compare:* continuous-time equation, difference equation,
differential equation, discrete-time equation, state-space model, Z
transform; *See Also:* first-order filter, integrator,
second-order filter, unit functions;

A
sensor that provides warnings for long, thin objects (like wires). It
has at least a 20deg x 30deg FOV, which is both velocity tracked and
pitch stabilized. It provides warnings (every 2.5 seconds) for long,
thin obstacles (like wires) at 400 meters detection range and contour
flight at 80-120 knots.

Related to latitude; across an aircraft left to right

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

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

A lateral flight director cue for
rotary-wing aircraft, primarily to control heading, by changing roll;
*Compare:* wheel cue; *Symbols:* Gamma sub 'LAT'; *Typical
Units:* percent,in;

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 Rate Gain, 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 selected
longitudinal guidance mode.

Position on earth, north or south of the equator;
*See Also:* astronomical latitude, geocentric latitude, geodetic
latitude; *Symbols:* Phi; *Typical Units:* rad, deg;

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

Low Frequency Automatic Direction Finding

Localizer

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;

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

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

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

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

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

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 a rotary-wing aircraft;

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;

Calculations for the longitudinal axis
of the guidance modes. The control law longitudinal axis input data
are: Reference Acceleration, Reference Acceleration Gain, Desired
Velocity, Velocity Error Scale Factor. The major output from
Longitudinal Guidance is the speed error for the selected longitudinal
guidance mode.

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

A filter that allows frequencies below
a cutoff frequency to pass while attenuating frequencies above the
cutoff frequency; *See Also:* first-order filter;

Low-pass filter

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

Heading of the aircraft relative to magnetic
north; A Magnetic Heading Sensor provides this heading data. *Symbols:* psi sub M; *Typical Units:* rad, deg;

Difference between true north and
magnetic north, varying with position; magnetic variation drifts with
time; *Symbols:* nu; *Typical Units:* rad, deg;

Magnetic variation

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

Equipment that produces a map image; *See Also:*
Digital Map Generator

Part of Instrument Landing System that
signals crew members of distance to runway, consisting of three
markers:. inner, middle, and outer;

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

A signal which indicates that one or more
caution lights has been activated (from MIL-STD-1472D);

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

Marker Beacon

Mission computer

Standard aviation term *See Also:*
above sea level;

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

Radius of the earth in the
east/west direction at a given position; *Synonyms:* earth radius
north/south; *Symbols:* rho sub M; *Typical Units:* ft; *Dimensions:* Length;

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

Mission processor;

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, navigation modes, radio navigation modes, guidance modes,
flight director modes, data source control information such as
frequencies; *See Also:* capture criterion

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

Microwave Landing System

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

A standard model for computing earth data

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

Mission processor

Mean sea level

A Multi-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
are processed and displayed as climb/dive commands on the Flight
Director display and E-squared 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 AGR mode allows the operators to determine the range to a
designated target, which can be used for position updates.

Magnetic variation

An enclosure on an aircraft.

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

Standard engineering term *See Also:*
second-order filter; *Symbols:* omega sub n; *Typical Units:*
rad/s,Hz; *Dimensions:* 1/Time;

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;

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

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;

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

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;

Navigation reference point

Obstacle avoidance

Outside Air Temperature

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

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

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

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.

How well is equipment operating; *Values:*
operational (all function and data is available), degraded (equipment
has partially failed with some function or data unavailable and some
available), failed (equipment has failed with no function or data
available);

Direction in reference to a coordinate frame

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

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

To alter selection made automatically by software

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

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

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

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

Periodic built-in-test

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 in modern aircraft;

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

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

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

A basic guidance mode,
providing lateral guidance to a PLS transmitter from range and bearing
inputs. Equipment that determines range and bearing to a personnel
with a PLS transmitter; Provides range and bearing to locate ground
personnel. Coded continuous or periodic interrogations of the
portable ground radios are used to provide the information.

Primary flight control system

A piece of equipment, a subsystem; *Synonyms:* device

Real-time engineering simulation

Total pressure

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

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

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

Personnel Locating System

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;
time integral of velocity; *Symbols:* p,P,x,y,z; *Typical
Units:* ft,nmi; *Dimensions:* Length;

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

Measure of exactness, possibly expressed in number
of digits, for example, computed to the nearest millimeter; *Compare:* accuracy

Most recently reported status words

Barometric pressure

Barometric altitude

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), and collective (rotary wing);

A standard set of four units to which all units
can be resolved; primary units are Mass(M), Length(L), Time(theta),
and Temperature(T); for example, standard units for velocity might be
kt (nmi/hr), ft/s, m/s, mph, but primary are always Length / Theta;
sometimes written with negative subscripts.

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

A system of representing attitude by measuring
angle of aircraft center line with respect to three orthoginal 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 while
producing results of the same accuracy *See Also:* Euler
parameters;

Radar Altimeter.

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 Terrain Reference Navigation algorithm for position updates.

Height with respect to the terrain below
(distance above closest dirt); *Synonyms:* above ground level;
*Symbols:* h sub r; *Typical Units:* ft; *Dimensions:*
Length;

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

A probability that a
percentage of one-dimension measurements will lie on a radial (line)
of given 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;

Navigation relative to radio station,
providing, for example, of relative bearing, range, lateral deviation,
and glideslope; Examples include VOR, TACAN, and PLS. Radio
navigation differs from 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 shut down 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. The Radio-
Navigation system accommodates this phenomenon by simulating range and
bearing to the fixed site when it is not transmitting. After
reacquiring a mobile transmitter, the mobile station's position is
re-determined. The navigation component supports wash-out filters on
output data.

Radar altitude select

Standard aviation term *Synonyms:* distance;
*Symbols:* r; *Typical Units:* ft,nmi - method of measurement
dependent on use; *Dimensions:* Length;

Act of determining a range

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;

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

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
execute with frequency 1/t execute in real time; Avionics systems must
run in real time;

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 often used 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 early insight in human factors problems, pilot complaints,
algorithm bugs, unstability in the algorithms, expected performance
(accuracy), and pilot-machine interaction; *Synonyms:* piloted
simulation; *Compare:* built-in simulation;

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

To absorb rf energy

Reference acceleration

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

A guidance control law
parameter, generated by the longitudinal guidance modes; *Typical
Units:* ft/s-squared, g; *Dimensions:* Length / Time-squared

A guidance control law
parameter, generated by the longitudinal guidance modes; *Typical
Units:* s; *Dimensions:* Time.

To disallow a position update, usually by an operator;
*Compare:* accept

Applies to measurements, in a non-standard, moving
reference, as opposed to fixed reference; *Compare:* absolute;

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

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

Signal Data Converter;

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

To approach a planned rendezvous point

Radial error probability

Data from a device

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

Ring-laser gyro

Root mean square;

Range

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

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

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

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;

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;

A helicopter;

Root sum square;

Remote terminal

Real-time engineering simulation

Remote Terminal Unit

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;

Continuous complex frequency plane; S-plane is used
in control systems engineering in the design of control laws *See
Also:* Laplace transform;

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

Signal Data Converter

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

A smoothing filter in which the output
follows the input, only more slowly; It is usually implemented 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 be noted 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 normalized variables, such as angles, the discontinuities
require special treatment.

A pattern of concentric arcs followed for
searching the ground from an aircraft; *Compare:* creeping line
search, expanding square search;

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
similar devices. *Compare:* derived, estimated, filtered,
measured, raw, smoothed

A test internal to a device

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

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

Measure of convergence of sensor data

Spherical error probability

Sensor Fusion/Correlation

To cease normal operations

*Symbols:* beta; *Typical Units:* rad,
deg;

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

A device that converts unique
signals to a standard protocol, usually MIL-STD-1553B; *Synonyms:*
Remote Terminal Unit;

A ratio of magnitude of a
desired signal to the magnitude of the noise received with it; *Typical Units:* dB;

Situational awareness provides the
pilots with information relative to the current surroundings, such as
other aircraft or threats in the immediate area.

Direct line distance, not along the ground;

A control surface on fixed-wing aircraft, usually
mounted to the aft edge of the wings, that extends the wing to provide
added lift at low speeds; *Compare:* flaps; *Symbols:* delta
sub S; *Typical Units:* rad, deg;

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

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

Signal-to-noise ratio

Signal-to-noise ratio

A standard model for computing earth data

Scalar velocity;

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

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

A probability that a
percentage of three-dimension measurements will lie within a sphere of
given radius, with the sphere centered at truth or mean of the
measurements; SEP specifies test cases for measurement errors of
sensors of three dimensions, such as velocity east, north, and
vertical. *Compare:* circular error probability, radial error
probability;

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

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

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

Total pressure

Units commonly encountered for a particular
quantity;

Data that defines aircraft parameters, such as
position, velocity, attitude; Some standard terms for state 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, magnetic variation,
grivation. earthspeed vector, vertical velocity, air mass flight path
angle, earth-referenced flight path angle, angle of attack, pitch,
radar altitude, barometric altitude, earth radius, glideslope, gravity
vector, lift vector, lateral acceleration vector, bank angle.

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 with matrices. *Compare:* continuous-time equation,
difference equation, differential equation, discrete-time equation,
Laplace transform, Z transform;

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

A structure on the ground, perhaps containing VOR or
TACAN

An indicator of how well a system or subsystem is
working

An binary indicator of a particular aspect
of a device; status indicators are independent of each other; status
indicators listed in this dictionary are derived from existing
programs. *See Also:* off, warning, operations, communications,
useability, initialization, test, maintenance, unknown;

Data words reported by devices to indicate
status; Each bit is defined on a device-by-device basis. 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.

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

Related to surface of water;

..

A survivability subsytem detects and counters
hostile actions.

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

Surface Wind Wave Motion

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

Terrain avoidance

Tactical Air Navigation;

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

A device for measuring angular velocity;

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;

Track angle error

Object or point pointed by FLIR or radar

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

True airspeed

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

Tacan

Tacan Point-to-Point

The contour of the earth;

Flight such that the aircraft
maintains a constant barometric altitude but flies around obstacles;
*Compare:* obstacle avoidance, threat avoidance;

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 above the terrain, usually in the range of 100-1,000
ft; Uses a g-command from the Multi-Mode Radar to generate a flight
director cue. This controls the aircraft flight path so that the set
clearance altitude is achieved over major high points in the terrain
with zero flight path angle. *Compare:* nap-of-the-earth flight;

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. TRN combines INS with map references.
It is most accurate over rough terrain. Does not give accurate data
while over flat areas or water. *See Also:* Digital Map
Generator;

Status words reported at the conclusion of
a test. *Values:* test in progress, not
tested, normal, redundant, degraded, failed;

Terrain following;

Threat avoidance

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

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

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

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

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

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;

Allowed error in measurements

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

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

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

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

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

Tracking is performed by the TRN

A device that receives and transmits

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

To radiate RF energy

A device that transmits

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 is controlled by the an operator or an autopilot; *Symbols:*
delta sub T; *Typical Units:* rad, deg;

Track

Terrain Referenced Navigation;

TRN with INS

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

Airspeed corrected for instrumentation
errors and air density; *See Also:* airspeed; *Symbols:* V sub
'TAS'; *Typical Units:* kt,ft/s; *Dimensions:* Length / Time;

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

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

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

To set the operating frequency or channel for a device

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

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 );

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

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

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

No units, such as ratios; a quantity with standard
units of 1; a quantity with primary units of 1; *Synonyms:*
dimensionless;

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

A system of fixed earth
coordinates, sometimes used instead of latitude and longitude,
accurate relative to others close by, such as ground troops;

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 the
device 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 as FLIR, MMR, or
radio navigation; a basic control to a data source from controls and
displays for updating a device *Compare:* aiding;

Universal Transverse Mercator

UHF/VHF Automatic Direction Finding

Rate of change of location, either scalar or vector,
often with subscripts such as ENU or XYZ to denote the coordinate
frame; time derivative of position; time integral of acceleration;
*Symbols:* v,V; *Typical Units:* kt,ft/s; *Dimensions:*
Length / Time;

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

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

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

Vertical speed hold

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

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

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

Calculations for the vertical axis, rather
than the longitudinal axis. The control law vertical axis input data
are: Desired Altitude, Altitude Integral, Altitude Integral Gain,
Altitude Integral Limit, Altitude Error Scale Factor, Magnitude limit
for delta altitudes. The major output from Vertical Guidance is the
altitude error for the selected vertical guidance mode.

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

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

Equipment that determines bearing to a
radio station with a VOR transmitter; VOR transmitters usually contain
ILS transmitters in addition to VOR; A basic guidance mode, providing
lateral guidance to a VOR station. A VOR/ILS/MB. radio receiver
provides a VHF Omni-Direction Range (VOR) function and Instrument
Landing System with Marker Beacon (MB) function. VOR provides
bearings to a fixed point (Localizer function); ILS/MB provides course
(localizer function) and glideslope deviations (Glide Slope (G/S)
function) during approach to a runway, along with marker beacon
indications. If VOR is collocated with a TACAN (VOR-TAC, or VORTAC),
bearing and range information is provided.

VHF Omnirange;

Collocation of VOR and TACAN providing distance and
bearing to station; a basic guidance mode, providing lateral guidance
to a set of a VOR station and a TACAN station that are collocated

A signal which alerts the operator to a dangerous
condition requiring immediate action (from MIL-STD-1472D); an
annunciator that is the most critical (more than an advisory or a
caution); Also, an indicator of potential failure soon; *Values:*
none, hot, low-power, high-power, other;

*See:* warning,
caution, advisory, annunciator, alert;

A filter to smooth a transition due to change
of input source, such as when changing modes; *See Also:*
transient-free switch;

A point on the ground, predefined as a point
of interest for the flight; a basic guidance mode, providing lateral
guidance to a waypoint, either by course or by direct (operator
selectable);

To approach a waypoint

Warning, Caution, Advisory

Indication of whether the aircraft has
weight on its wheels, meaning airborne or on the ground; weight on
wheels can be detected by a sensor on the wheels, computed from other
state data, or a combination;

World Geodetic Survey 1972

World Geodetic Survey 1984

A flight control operated by turning with hands in
fixed-wing aircraft, primarily to control roll (heading) via the
ailerons; wheel is connected to yoke;

A lateral flight director cue for fixed-wing
aircraft, primarily to control heading, by changing roll; *Compare:* lateral cyclic cue; *Symbols:* Gamma sub 'LAT' ; *Typical Units:* percent,in;

*Symbols:* B sub W; *Typical Units:*
rad, deg;

*Symbols:* V sub W; *Typical Units:*
kt,ft/s; *Dimensions:* Length / Time;

A standard model for
computing earth data;

A standard model for
computing earth data;

Weight on wheels

A test to send data to a device having it sent back
unaltered

Waypoint

Crosstrack deviation

Crosstrack deviation rate

A standard aircraft coordinate frame and sign convention,
where nose, right wing, and down are positive X, Y, and Z,
respectively; often used as subscripts; *Compare:* east-north-up;

Angle of heading; *Symbols:* psi,Psi; *Typical
Units:* rad, deg;

Rate of change of yaw; time derivative of yaw; *Symbols:* r; *Symbols:* psi dot; *Typical Units:* rad/s,
deg/s; *Dimensions:* 1/Time;

A flight control operated by pushing and pulling with
hands in fixed-wing aircraft, primarily to control pitch (altitude)
via the elevators; yoke is mounted on a column between the operator's
legs, positioned much like a steering wheel in a car; yoke control is
achieved by pushing and pulling the wheel to move the column (yoke)
fore and aft;

A vertical flight director cue for fixed-wing
aircraft, primarily to control altitude, by changing pitch; *Compare:* collective cue; *Symbols:* Gamma sub VERT; *Typical
Units:* percent,in;

Discrete complex frequency plane; Z-plane is used in
control systems engineering in the design of control laws *See
Also:* Z transform;

A mathematical relationship to model a discrete
function in the complex frequency domain (Z-plane); Z transforms are
commonly used by systems engineers to describe avionics systems; *Compare:* continuous-time equation, difference equation, differential
equation, discrete-time equation, Laplace transform, state-space
model; *See Also:* first-order filter, second-order filter, unit
functions;

Zone of confusion

A circular area centered at a TACAN
station in which bearing is extremely noisy;

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Wed Dec 7 14:06:46 EST 1994