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OSWEGO - Avionics Dictionary Category: Electronics and Engineering > Avionic terms Date & country: 11/08/2008, USA Words: 560

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

Magnetic heading.
Heading of the aircraft relative to magnetic north; A Magnetic Heading Sensor provides this heading data. Symbols: psi sub M; 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.
Equipment that produces a map image; See Also: Digital Map 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 (from MIL-STD-1472D);

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

MB.
Marker Beacon

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 radius north/south; Symbols: rho sub M; Typical Units: ft; Dimensions: Length;

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

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, navigation modes, 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.
A standard model for computing earth data

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

MP.
Mission processor

MSL.
Mean sea level

Multi-mode radar (MMR).
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...

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 and less 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 aid.
A device or process to help with navigation, such as a VOR station 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;

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;

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

Normalizer.
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 and function is available.

Offset.
Part of received data that is undesired, consisting of a random, time-invariant term added to a signal; 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; 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);

Orientation.
Direction in reference to a coordinate frame

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 in modern aircraft;

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

Periodic built-in-test (PBIT).
Selftests running internal to a device as part of normal operation; Compare: initiated built-in-test;

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

Personnel Locating System (PLS).
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.

PFCS.
Primary flight control system

Physical device.
A piece of equipment, a subsystem; Synonyms: device

Piloted simulation.
Real-time engineering simulation

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

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

Pitot pressure.
Total pressure

PLS.
Personnel Locating System

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

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

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 altitude.
Barometric altitude

Pressure.
Barometric pressure

Primary units.
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.

Prime radius of curvature.
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;

Quaternion.
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...

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 Terrain Reference Navigation algorithm for position updates.

Radar altitude select (RALT SEL).
A basic guidance mode, providing vertical guidance to an operator selected radar altitude;

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;

Radial error probability (REP).
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;

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 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 be...

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

Reasonableness.
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

Receive.
To absorb rf energy

REFACC.
Reference acceleration

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.

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

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

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

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

Remote terminal (RT).
Term defining role of a device on a MIL-STD-1553 bus as being a slave; Compare: bus controller;

Remote Terminal Unit.
Signal Data Converter;

Rendezvous approach.
To approach a planned rendezvous point

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

REP.
Radial error probability