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Glossary of Aviation Terms


AAIB: Air Accident Investigation Branch: British equivalent of NTSB

a/c: Aircraft

AC — Advisory Circular:  Sent by the FAA to operators and maintenance facilities advising them of a problem or malfunction which has begun to show up in multiple aircraft or components.

a/l: Airline

ACAS: Aircraft Collision Avoidance System:  Early relative of the now operational TCAS (Traffic Alert and Collision Avoidance System) which warns pilots of potential conflicts with other aircraft

AD — Airworthiness Directive: FAA regulatory notice which mandates repairs or modifications on an aircraft or aircraft component which have shown to be a safety of flight risk.

A/D: Analog-to-Digital

Ada: A higher order programming language developed during the 1970s for the DOD (note: not an acronym, named for first computer programmer, Ada Augusta Byron)

ADC — Air Data Computer:  A device that takes information from a variety of mechanical sensors mounted on the aircraft, such as airspeed and altitude, and formats that information for use by Flight Management Systems, autopilots, and cabin displays.

ADF — Automatic Direction Finder: a navigation receiver based on the AM radio band;  a very simple device which literally points towards the station that is tuned in.  First fielded in the 1930s, it is very useful for listening to news and country/western music in flight.

ADI — Attitude Director Indicator:  An instrument that provides an “artificial horizon” for use by the pilot to display whether the aircraft is flying straight and level or turning, level flight or climbing or descending.

ADIRS — Air Data Inertial Reference System:  A Honeywell product using Ring Laser Gyros to provide both attitude and position information for use by Flight Management Systems

ADIRU — Air Data Inertial Reference Unit :  A Honeywell product blending analog Air Data information with Ring Laser Gyro generated attitude and inertial information

ADM: Air Data Module

ADR: Air Data Reference

ADS: Air Data System

ADS: Automatic Dependent Surveillance: A system for aircraft position reporting, e.g., via SATCOM now in use in the Pacific Ocean airway system whereby an aircraft reports it’s GPS derived position to Air Traffic Control via a satellite communications link.

ADS-B — ADS-Broadcast:  The system used to send autonomously derived position information to Air Traffic Control for traffic separation in remote areas, currently in use in the Pacific Ocean airways structur.

ADT — Air Data Tester:  A unit used by technicians to transmit data to Air Data Computer systems in order to establish a baseline test and assure that the unit is functioning properly prior to flight.

AEEC — Airlines Electronic Engineering Committee:  A group which determines standards by which airline aircraft are built, maintained and operated.

AES — Aircraft Earth Station:  A communications facility which receives, processes and forwards ADS-B information as well as airborne telephone traffic.

AFCS —Automatic Flight Control System:  A “global” name for the package of equipment used to navigated and control an aircraft.

AFIS — Airborne Flight Information Service:  An automatic, pre-recorded series of messages which called be received either when airborne or via telephone on the ground detailing the weather conditions, which runway is in use and any special notifications at a specific airport.  Each airport will have its AFIS broadcast on a discreet frequency in the VHF band (108 – 125 MHz)

AFMS — Advanced Flight Management System:  Proprietary Honeywell name for its latest offerings within the FMS/Flight Control market

AFS — Auto Flight System: MD-11, integrates autopilot, CAT II flight director and autothrottle functions.   A Honeywell product specifically designed for the MD-11 aircraft integrating all flight control functions.

AGL — above ground level:  A measurement of altitude; In aviation, altitudes are reported in two flavors, AGL and MSL.  MSL, or Mean Sea Level is a barometrically derived figure used as the standard by air traffic control.  AGL is important in that it defines how high you are above something that you could, potentially, run into.

AHRS — Attitude-Heading Reference System:  (Pronounced AY-HARS)  Provides display and navigation equipment with information regarding the aircraft’s attitude (climbing, descending, turning or straight and level) and the direction it is moving, utilizing either traditional or ring laser gyros.

AHS — American Helicopter Society:  Clearinghouse for helicopter related information

AIA — Aerospace Industries Association:  Lobbyists

AIAA — American Institute of Aeronautics and Astronautics:  Clearinghouse for “pure” research

AIM — Airman’s Information Manual:  Published by the FAA, it contains everything from how to fly and navigate an aircraft to every Federal Aviation  Regulation (FAR) in existence.

AIMS — Airplane Information Management System (Boeing 777):  Honeywell proprietary acronym for their processing unit which manages the flow of information to and from sensors to and from the AFMS on the Boeing 777

ALPA — Airline Pilots Association:  The largest and most powerful pilots union.

ALT: Altitude

ALTN — alternate (airport):  A designation on a flight plan of the airport you will go to if, for some reason, you cannot get to the airport you wanted to get to.

AM: Amplitude Modulation

AMC — Avionics Maintenance Conference:  A clearinghouse for airline maintenance information

AMD — Advisory Map Display:  Honeywell product which displays hazards to navigation

AMI: Airline Modifiable Information

AMLCD: Active Matrix Liquid Crystal Display

AMOS: Airline Maintenance and Operation Support System

AMSS: Aeronautical Mobile Satellite Service

ANSI: American National Standards Institute

ANSIR: Advanced Navigation System Inertial Reference

ANP: Actual Navigation Performance

AOA —angle-of-attack:  The angle of the aircraft relative to the horizon; i.e. is the nose above, or below the horizon

AOG — Aircraft-On-Ground:  The three most hated letters in airline maintenance:  It refers to the fact that, because something is broken, the aircraft can’t fly.

AOPA — Aircraft Owners and Pilots Association:  Ask your dentist, he probably belongs.

A/P — Autopilot:  Also known as “George” for reason or reasons unknown.

APU — Auxiliary Power Unit  A small turbine engine mounted internally within the aircraft structure to provide electrical and pneumatic power to an aircraft.  Most can be used in flight in the event of a generator or hydraulic pump failure

ARINC — Aeronautical Radio Inc.: A nonprofit corporation owned by member airlines to define form, fit and function of avionics equipment

ARNIC 429: Standard for broadcast digital information transfer systems for general applications

ARNIC 561: Inertial navigation system specifications

ARNIC 571: Inertial sensor attitude-heading reference system specifications

ARNIC 575: Digital air data system specifications

ARNIC 700-series: All-digital equipment specifications for new-generation transport category aircraft.

ARSA — Airport Radar Service Area:  Within this area, all aircraft must be in radio contact with ATC and, unless specifically permitted, equipped with a transponder for positive identification.

ASC — Aircraft System Controllers: MD-11, computers and control panels that automate many of the flight engineer control/monitoring functions from the DC-10.

ASCB : Avionics Standard Communication Bus

ASCII: American Standard for Information Exchange

ASE: Airline-Selected Equipment: vs. SFE; see also BFE

ASI — Airspeed Indicator:  Tells a pilot how fast he is moving through the air, but not necessarily how fast he is moving over the ground.

ASIC: Application-Specific Integrated Circuit

ASL — above sea level:  Barometrically  derived standard altitude used by aircraft and ATC.

ASME: American Society of Mechanical Engineers

ASRS — Aviation Safety Reporting System:  A NASA program to determine both fault and failure trends in equipment as well as mistakes made by pilots and air traffic controllers; the latter can be reported anonymously.

A/T — autothrottle:  A system that controls multiple engines in sync, setting power to control speed and/or altitude during all flight regimes.

ATA — Air Transport Association:  Airline lobbyists

ATC: Air traffic control

ATCRBS: Air Traffic Control Radar Beacon System

ATE: Automatic Test Equipment: e.g., the STS-1000

ATI — Air Transport Indicator: Standard case sizes ranging nominally from 2ATI – 6ATI. The number at the beginning of the designation refers to the size of the indicator in inches; i.e. a 2ATI instrument would be two inches across at its widest dimension

ATLAS: Abbreviated Test Language for Avionics Systems

ATM: Air Traffic Management

ATN — Aeronautical Telecommunications Network:  A worldwide system to provide inflight telephone service to business and commercial aircraft.

ATR — Air Transport Radio: ARINC form-factor/standard case dimensions; 1 ATR = 8 MCU (also, Austin Trumbull Radio standard design)  i.e., how big the boxes the avionics are contained  within.

ATS: Air Traffic Services

AUSRIRE — All Union Scientific Research Institute of Radio Equipment: CIS (former Soviet) agency similar to ARINC.

AWLU — Aircraft Wireless LAN Unit:  Infrared system for connecting in flight personal computers to an airborne LAN.

AZ — azimuth: Angular measurement in horizontal plane, measured in degrees.


BAe: British Aerospace

BCA: Boeing Commercial Airplanes

BCAS — Beacon Collision Avoidance System: Forerunner of TCAS, origiginally designed in the early ’60s following the collision of two aircraft over the Grand Canyon.

BEA — Bureau d’Enquetes Accidents: French equivalent of NTSB.

BFE — Buyer-Furnished Equipment: Not supplied as standard equipment by airframe manufacturer; selected by customer (see ASE).

BIT: Built-in Test

BITE: Built-in Test Equipment

BPS: Bits Per Second

B-NAV — Basic Area Navigatin: Concept of easing congestion in European airways by requiring aircraft to be fitted with equipment that will allow more direct routings by ATC.


CAA: Civil Aviation Authority (United Kingdom and other countries).

CAB: Civil Aeronautics Board

CAD/CAM: Computer Aided Design; Computer Aided Manufacture

CADC — Central Air Data Computer: An analog system.

CAS — Calibrated Airspeed:  A figure derived by taking into consideration temperature, barometric pressure and altitude.

CAT — clear air turbulence: High altitude turbulence encountered where no clouds are present.

CAT I — Category I flight conditions: Allows operation down to a 200 feet decision height (DH) and with runway visual range not less than 2,600 feet.

CAT II — Category II flight conditions: Procedure that provides for approach to height above touchdown not less than 100 feet, runway visual range not less than 1,200 feet.

CAT IIIA — Category IIIA flight conditions: No decision height minimum, runway visual range not less than 700 feet.

CAT IIIB — Category IIIB flight conditions: No decision height minimum, runway visual range not less than 150 feet.

CCA: Circuit Card Assembly

CDI — Course Deviation Indicator:  A simple pointer used to display where the aircraft is heading versus where the pilot would like it to be headed.

CD-ROM: Compact Disc-Read Only Memory

CDS: Common Display System

CDU: Control-Display Unit: part of FMS

CFI: Controlled Flight Into Terrain

CG — Center of Gravity:  A point at which an aircraft can, theoretically, be balanced upon a pin, albeit a very strong pin.

CMC — Central Maintenance Computer:  A sensor/computer combination on modern aircraft that stores any operational anomalies for downloading by maintenance personnel to help direct repair and maintenance efforts.

CMOS: Complementary Metal Oxide Semiconductor

CMU: Communications Management Unit:  A central processing unit in modern aircraft that manages all frequencies for both communications and navigation.

CNS/ATM: Communication, Navigation, Surveillance/Air Traffic Management (supersedes “FANS” terminology)

COTS: Commercial Off-The-Shelf

CPA — Closest Point of Approach (TCAS):  How close the airplane you almost hit REALLY was.

C/PDLC — Controller/Pilot Data Link Communications:  Basically, the airborne equivalent of a chat room between pilots and air traffic controllers using the ACARS datalink or SATCOM.

CRM — Cockpit Resource Management, or Crew Resource Management: The definitive assignment and sharing of tasks within a cockpit crew that defines who is the Pilot In Command (PIC) and who is the Pilot Not Flying (PNF)  The PIC is responsible for actually flying and controlling the aircraft in flight, while the PNF responsibilities are generally to navigate and communicate.  This flight crew philosophy was most ably demonstrated during the United Flight 262 crash in Sioux City, Iowa, during which the Captain made the best use of his available cockpit resources by assigning individual and irrevocable responsibilities to each crew member. (The latter term has tended to displace former, recognizing a broader scope of the concept.)

CRT — Cathode Ray Tube: Display unit

CVR: Cockpit Voice Recorder.


D/A: Digital-to-Analog Conversion

DADC: Digital Air Data Computer

DASA: Deutsche Aerospace (German aerospace organization)

dB – decibel: Acoustic measurement unit

DEU — Display Electronics Unit:  The CPU which produces the displays on Electronic Flight Instrument System screens.

DFDAU — Digital Flight Data Acquisition Unit:  Used in aircraft test flights.

DFDR — Digital Flight Data Recorder:  Records hundreds of performance parameters while an aircraft is in flight, often used to determine what went wrong.  Records a half hour of data on a digital “loop” format.

DG — Directional Gyro: Device that uses a gyroscope to determine in what direction the aircraft is moving.

DGAC — Direction Generale de l’Aviation Civile: French certifying authority, equivalent of FAA

DGPS — Differential GPS:   A means of increasing the accuracy of airborne GPS position information by positioning a GPS receiver on the ground in a known, surveyed location.  The receiver then takes that location, compares it with the position it is computing using the data from GPS satellites, and transmits a correction factor to DGPS-equipped aircraft.  This allows DGPS navigation equipment to measure errors in inches.

DH — Decision Height:  The height at which a flight crew must decide to continue a landing approach or to break it off and go around for another approach attempt because they are not able to see the runway.

DME: Distance Measuring Equipment

DO: Dornier

DOT: Department of Transportation (U.S.)

DR — deduced reckoning:  The digital equivalent of dead reckoning.

DRAM: Dynamic Random Access Memory

DU — Display Unit:  A cockpit display screen.

DUATS — Direct User Access Terminal System:  A means of filing flight plans, getting weather information, etc.,  provided to personal computer users by GTE


EADI: Electronic Attitude Direction Indicator (see ADI).

EEPROM: Electrically Erasable Programmable Read-Only Memory

EFIS: Electronic Flight Instrument System, an advanced display system using either CRT or AMLCD displays to present information on flight and engine parameters to flight crews.

EHSI: Electronic Horizontal Situation Indicator (see HSI).

EIA — Electronic Industries Association:  Lobbying group

EICAS — Engine Indication and Crew Alerting System:  A system that under normal conditions will display engine and systems parameters, such as RPM, fuel consumption and amount. In the event of an anomaly, an EICAS will display information specific to the anomaly.  For example, if the number two engine oil pressure drops below normal values, a amber alert will be flashed on an EICAS screen, and a detailed message describing the problem will follow.

EMI: Electromagnetic Interference. Why airlines don’t want you talking on cell phones in flight.

EPR — Engine Pressure Ratio:  A figure that tells pilots how much power their engines are producing. It is derived from an air pressure sensor at the front of the engine and one in the rear. The higher the ratio, the more power being produced. It is also used as a power setting for autothrottle system during takeoff. The FMS computer determines the minimum amount of power needed for departure and sets that parameter on the autothrottles; this technique, known as Flex-EPR, saves fuel and engine wear.

EPROM: Erasable Programmable Read-Only Memory

EPRT: Engine Pressure Ratio Transmitter. Sensor for EPR system.

EROPS: Extended Range Operations

ETA: Estimated Time of Arrival

ETE: Estimated Time En route

ETP: Equal Time Point. Halfway there, by time.

ETOPS — Extended Twin-engine Operations:  A certification criteria used for large twin engine operations. According to this certification, a twin may not be more that the certified time from land in over-water operations.


FAA: Federal Aviation Administration (U.S.)

FADEC — Full Authority Digital Engine (or, Electronic) Control:  The interface between throttles and the engine.

 FANS: Future Air Navigation System (ICAO-endorsed worldwide navigation plan — the term “CNS/ATM” is now preferred).

FAR: Federal Aviation Regulations

FBO — Fixed-Base Operator: The aircraft equivalent of a full-service gas station.

FBL — Fly-by-light:  A control architecture using fiber optics to route control and sensor information.

FBW — Fly-by-wire:  A control architecture using wire to route control and sensor information.

CC: Federal Communications Commission (U.S.) Also Flight Control Computer.

FCS: Flight Control System

FD — Flight Director:  A display indicator, combining an artificial horizon with a set of “command bars” that indicate whether the pilot should turn, climb or both to navigate the aircraft to the desired point.

FDR: Flight Data Recorder

FL — Flight Level: Measured in hundreds of feet (above 18,000 feet). Used as a standard to request (on the part of ATC) or report an altitude.  A typical request would be, “United four-two, climb and maintain flight level three one zero.”  ATC has asked United Flight 42 to climb to 31,000 feet and stay there.

FLIR — Forward Looking Infra-Red (radar):  A sophisticated device that images heat signatures.

FM: Frequency Modulation

FMC: Flight Management Computer

FMCDU: Flight Management Control and Display Unit (FMS)

FMCS: Flight Management Computer System

FMGC: Flight Management Guidance Computer

FMGEC: Flight Management Guidance Envelope Computer

FMS: Flight Management System

F/O: First Officer

FOD: Foreign Object Damage

FOG: Fiber Optic Gyro (see IFOG)

FSC: Fuel System Controller

FT/ADIRS: Fault Tolerant/Air Data Inertial Reference System (777)


GA — general aviation: Aviation operations other than military and airlines (e.g., corporate, agricultural, personal, flying clubs/schools).

GATM: Global Air Traffic Management (military version of CNS-ATM concept).

GATT: General Agreement on Trade and Tariffs

GCP — Glareshield Control Panel:  A separate panel mounted at the top of the instrument panel, generally used to control autopilot and some FMS functions

GES — Ground Earth Station: Used to route satellite telephone calls (a SATCOM term).

GIE — Groupment d’Intérêt Economique: French corporate entity, grouping of mutual economic interests (e.g. Airbus)

GLONASS — Global Orbiting Navigation Satellite System: CIS satellite navigation system version of GPS, designed during the existence of the Soviet Union. Similar, down to frequencies used, to U.S. GPS equipment and in fact is used in some receivers for a ‘blended” navigation solution.

GLS: GPS Landing System

GLU: GPS Landing Unit. Provides precision of GPS guidance to the runway in Cat III operations

GMT — Greenwich Mean Time: used in navigation systems; Zulu

GO/NG — Go/No Go: The point at which it’s either going to fly or it’s not.

GPIRS — Global Positioning/Inertial Reference System:  A blended navigation system using both GPS and Intertial Reference System information.

GPS: Global Positioning System

GPSSU: Global Positioning System Sensor Unit

GPWS — Ground Proximity Warning System:  A system using downward-looking, low power radio sensors to alert the crew that the ground is about to smite them.

GS — Groundspeed:  The speed at which an airplane is moving over the ground, computed in an aircraft by taking the airspeed and adding or subtracting headwinds or tailwinds.  Example:  Airspeed 100 MPH with a tailwind of 20 MPH equals a groundspeed of 120 MPH.

G/S — Glide Slope:  An indicator that displays the aircraft position in relation to an ideal approach path to a runway.  Also a sloping approach path to the end of a runway.


HAI — Helicopter Association International:  Lobbying organization for helicopter pilots, operators and manufacturers.

HERF — High-Energy Radio Frequency or High-Energy Radiated Fields: Dense electromagnetic fields created by radio and TV transmitters, a possible source of interference for electronic instruments

HF — High Frequency: 3-30 MHz

HFDL: High Frequency Data Link

HIRF: High Intensity Radiated electromagnetic Frequencies (see HERF)

HPA: High Power Amplifier, SATCOM component

HSI — Horizontal Situation Indicator:  A cockpit display resembling a compass with individual pointers signifying the orientation of individual navigation sources in relation to the aircraft.

HUD — Head-up Display:  A projected display allowing the pilot to see out of the cockpit while being able to monitor key flight indicators which are shown by the HUD.

HW: Hardware

Hz — Hertz: Measure of frequency of cycles per second, named for scientist Heinrich Hertz.


IAS: Indicated Airspeed

IATA — International Air Transport Association: Economic association of commercial airlines.

ICAO — International Civil Aviation Organization: Agency of the United Nations that works to establish international standards, recommended practices and procedures covering the technical fields of aviation.

IDENT: Identification

IEEE: Institute of Electrical and Electronics Engineers

IFALPA: International Federation of Airline Pilots Association

IFE: In-flight entertainment

IFOG: Interferometric Fiber Optic Gyro (see FOG).

IFR: Instrument Flight Rules (see IMC).

IL: Ilyushin Design Bureau

ILS — Instrument Landing System:  A system of tightly focused transmitters located at the end of a runway that provides flight guidance information to flight crews.

IM: Inner Marker (glideslope).

IMC: Instrument Meteorological Conditions (see IFR).

Inmarsat — International Maritime Satellite Organization: Cooperative of more than 50 countries that operates a global system of satellites for mobile communications, such as SATCOM.

INS: Inertial Navigation System

I/O: Input/Output

IPTN — Industri Pesawat Terbang Nusantara: Indonesia’s state-owned aerospace manufacturer.

IR: Infrared

IRS: Inertial Reference System

IRU: Inertial Reference Unit: part of IRS

ISA — International Standard Atmosphere:  A baseline temperature and altitude (68 degrees F at sea level) used to establish performance figures for aircraft, i.e., an aircraft is capable of taking off in 2,000 feet on a “standard” day.

ISDU: Inertial System Display Unit

ISO: International Standards Organization

IVSI — Instantaneous Vertical Speed Indicator:  An instrument that tells a flight crew how quickly the aircraft is climbing or descending.


JAA —(European) Joint Airworthiness Authority: Founded in 1970 to develop unified European approach to aviation safety; represents 27 European countries. (See also JAR)

JAR: Joint Airworthiness Requirement, issued by JAA


K: Thousand

KHz: KiloHertz

KIAS — Indicated Airspeed in Knots:  Format displaying airspeed.

KT — Knots: Nautical miles per hour (miles per hour times 1.15).


LAAS — Local Area Augmentation System:  An offshoot of the Differential GPS system used over a wider area than that used for approaches and landing.

LADGPS — Local area differential GPS:  Another term for LAAS.

LAN: Local Area Network

LASER: Light Amplification by Simulated Emission of Radiation

LAT: Latitude

LCD: Liquid Crystal Display

LED: Light-Emitting Diode

LEO: Low Earth Orbit

LIDAR — Light Detection and Ranging:  A system of measuring the distance to an object using a short burst of light (generally in the infrared spectrum) and measuring the time from emission to reception of the reflected light and dividing that number by the speed of light, thereby determining the distance.

LIP: Limited Installation Program (e.g. TCAS)

LLWAS — Low-Level Wind Shear Alert System:  A system which measures the characteristic increase, stagnation and sudden decrease in windspeed found in a thunderstorm generated windshear at an airport.

LNAV: Lateral Navigation

LOC — Localizer: Part of Instrument Landing System.

LORAN — Long-Range Navigation: Electronic pulse system for oceanic navigation.  First install in the 1920s, the system is being phased out in faovr of satellite navigation.

Loran-C: A hyperbolic grid navigation system.

LRU: Line-Replaceable Unit

LRM: Line-Replaceable Module

LSAS: Longitudinal Stability Augmentation System (MD-11)

LSI: Large Scale Integration

LSRRTI: Leningrad Scientific Research Radio Technical Institute

LSS — Lightning Sensor System:  Also known as a “StormScope,” this system detects the radio frequencies emitted by lightning and displays their location on a screen.


mb: millibars

M — Mach number: Speed of aircraft expressed in relation to speed of sound.

M: Million; mega

MAC — Mean Aerodynamic Chord:  A measurement of the curved, upper area of a wing from the center of the leading edge (front part of the wing) to the trailing (rear) edge.

MASI: Mach Airspeed Indicator

MCA: Ministry of Civil Aviation (former USSR).

MCDU: Multifunction Control and Display Unit. Part of the Flight Management System.

MCP —Mode Control Panel:  Autopliot control

MCU: Modular Concept Unit (Spitzer), also defined as Minimum Configuration Unit (BCA Magazine). Also, Modular Component Unit.

MD: McDonnell Douglas (no hyphen)

MDAU: Maintenance Data Acquisition Unit

MEO: Medium Earth Orbit (satellite)

MFD: Multi-Function Display

MHRS — Magnetic Heading Reference System:  Basically, a very sophisticated compass.

MHz: MegaHertz. Millions of Hertz, or cycles per second.

MLS — Microwave Landing System:  A military-derived landing system using extremely high frequency emissions to provide flight crews with approach guidance.  Its civilian deployment was overshadowed by the proliferation of GPS approach guidance.

MM — Middle Marker (glideslope):  A low power beeping tone is transmitted from the ground to give flight crews an aural alert as to their position during an instrument approach, letting them know, basically, that they have flown roughly halfway to the runway.

MMR: Multi-Mode receiver

MNPS — Minimum Navigation Performance Specifications:  A figure established by ICAO countries for trans-oceanic travel that sets the maximum navigation error allowable for use on these flight routes.

MOPS: Minimum Operation and Performance Standards/Minimum Operational Performance Standards

MOU: Memorandum of Understanding (plural, Memoranda)

MSL: Mean Sea Level (datum for altitude measurement)

MSU: Mode Select Unit

MTBF —Mean Time Between Failures:  How long a piece of equipment can be expected to perform before a failure, measured in hours that equipment is operating.

MTBR — Mean Time Between Removals:  How long before you can expect to have to take a malfunctioning piece of equipment out for repairs.

MTBUR: Mean Time Between Unscheduled Removal

MTU: Motoren-und Turbinen Union Ludwigsfelde GMBH, a German engine manufacturer.


N1: Engine low pressure rotor speed. How fast the first set of turbine blades in a jet engine are turning.

NAS: National Airspace System

NASA: National Aeronautics and Space Administration (U.S.)

NAT — North Atlantic Tracks:  A series of trans-oceanic flight paths from the United States to Europe and vice versa, assigned to departing and arriving aircraft.

NAV: Navigation

NAVAID: Navigational Aid

NAVSAT: Navigation satellite

NBAA: National Business Aviation Association

NCD: No Computed Data

ND: Navigation Display

NDB — Nondirectional Beacon:  Generally an ADF transmitter located at or near an airport that allows a flight crew to “home in” on the signal and fly to the vicinity of the airport.  Older technology.  Also known as Nav Data Base.

NM — Nautical Mile: 1.15 statute miles or 1,000 fathoms or 216,000 barleycorns; 60 nm = 1 degree of earth’s circumference

NMS: Navigation Management System

NMU: Navigation Management Unit

NOAA: National Oceanic and Atmospheric Administration

NOTAM — Notice to Airmen:  Notices issued to pilots and flight crews detailing a change or changes at an airport, i.e., if a runway is closed for repairs, a NOTAM will be issued to that effect.

NPRM — Notice of Proposed Rule-Making (FAA):  Prior to issuing an Airworthiness Directive, which is in effect, a change in the Federal Aviation Regulations pertinent to a particular aircraft or component, the FAA will issue an NPRM advising that such a change is coming and asking for comments or suggestions on the proposed directive.

NTSB: National Transportation Safety Board (U.S.)

NWS: National Weather Service (U.S.)


OAT: Outside Air Temperature

OEM: Original Equipment Manufacturer

OM: Outer Marker (glideslope).  An aural alert broadcast to pilots making them aware that they are at the farthest point of the approach to a runway.

OMS: On-Board Maintenance System

ORT: Owner Requirements Table


PFD: Primary Flight Display

PIREP — Pilot Report: If a pilot encounters a significant weather condition, i.e., turbulence, icing or rain, he or she will broadcast that back to ATC in the form of a PIREP.

PMAT: Portable Maintenance Access Terminal

PMS — Performance Management System: The computer system which controls, among other things, the Autothrottle system

PRF: Pulse Repetition Frequency. Pertaining to radar.

PROM: Programmable Read-Only Memory

Ps: Pressure, static. Air data measurement

psi: Pounds per square inch

Pt — Pressure, total: Air data measurement

PWB: Printed wire board


QFE: Field elevation pressure; a term used in the United Kingdom by ATC and pilots.

QNH: Sea level pressure; a term used in the United Kingdom by ATC and pilots.


RA — Radio Altitude:  Measurement of the aircraft’s altitude above ground during a landing approach determine by a small radar altimeter.

RA — Resolution Advisory (TCAS):  An alert generated by a TCAS (ant-collision system) that tells the flight crew to climb or descend in order to avoid a midair collision.

RAA: Regional Airline Association

RADAR: Radio Detection And Ranging

RAE: Royal Aircraft Establishment (Farnborough)

RAIM: Receiver autonomous Integrity Monitoring (GPS)

RAM: Random Access Memory

RDI: Radio Direction Indicator, also known as an ADF.

RF: Radio frequency

RFI: Request For Information

RFP: Request For Proposal

RFQ: Request For Quotation

RFU: Radio Frequency Unit – SATCOM component

RHF: Ridiculously High Frequency

RISC: Reduced Instruction Set Computer

RLD: Rijks Luchtvaart Dienst, the Dutch equivalent of FAA

RLG: Ring Laser Gyro

RMI: Radio Magnetic Indicator

RMU: Radio Management Unit

RNAV: Area Navigation

RNP: Required Navigation Performance

ROM: Read-Only Memory

RPK — Revenue Passenger-Kilometers: Number of revenue passengers carried times distance in KMs

RPM: Revenue Passenger-Miles (see RPK)

RPZ: Ramensky Priborostroitelny Zavod (Russian avionics manufacturer).

R/T: Receiver/Transmitter

RTA: Required Time of Arrival

RTCA: A private, not-for-profit organization that brings industry and government together to address the needs of the worldwide aeronautical community. The acronym RTCA originally stood for Radio Technical Commission for Aeronautics, but is now known simply as RTCA.

RVR: Runway Visual Range

RVMS: Reduced Vertical Separation Minimums


SA: Selective Availability

SAE: Society of Automotive Engineers

SAIFIR: Systems Aid for Integration and Fault Reporting (777)

SAMPE: Society for the Advancement of Material and Process Equipment

SAR: Search and Rescue, usually pertaining to weather radars and navigation (Beacon Collision Avoidance System).

SARPS: Standard and Recommended Practices

SAT: Static Air Temperature

SATCOM: Satellite Communications

SC: Special Committee (RTCA term).

SDU: Satellite Data Unit, a SATCOM component.

SFE: Seller-Furnished Equipment, i.e., selected by airframe manufacturer as standard for that aircraft type.

SID: Standard Instrument Departure

SIGMET — Significant Meteorological Advisory:  Broadcast to pilots advising them, for example, of thunderstorms or heavy turbulence

SITA: Société Internationale de Télécommunications Aéronautiques, a cooperative, not-for-profit organization with 400 member companies dedicated to the air transport industry. Operates world’s largest specialized data telecommunications network, including VHF AIRCOM Service, which provides an air-ground communications network of ground stations.

SITS: Subsystem Integration and Test Station

SLS: Satellite Landing System,  a GPS based instrument landing system.

SMART: Standard Modular Avionics Repair and Test

SMT: Surface-Mount Technology

SRC: Systems and Research Center

STAR: Standard Terminal Arrival Route

STC: Supplemental Type Certificate. FAA certification document issued to companies that perform significant modifications on an aircraft.

STOL: Short Take-Off and Landing

SW: Software


TA: Traffic Advisory (TCAS)

TAS: True Airspeed

TAT: Total Air Temperature

TBD: To Be Determined

TCA: Terminal Control Area

TCAS: Traffic Alert and Collision Avoidance System

TERPS: Terminal Instrument Procedures

TO/GA: Take Off/Go Around, operating mode.

TRACON: Terminal Radar Approach Control

TSO: Technical Standard Order, performance specification and production compliance document issued by FAA.

TTG: Time To Go

TTS: Time To Station

TTW: Time to Waypoint

Tu: Tupolev Design Bureau

TURB: Turbulence

TWDL: Two-way Data Link


UDF: Unducted Fan. A turbine engine with the “fan” section enlarged and exposed for greater performance.

UHF: Ultra High Frequency, 300-3000 MHz


V/STOL: Vertical/Short Takeoff and Landing

V1: Takeoff decision speed

V2: Minimum takeoff safety speed at 35 feet.

VAC: Volts, Alternating Current

VASI: Visual Approach Slope Indicator. A series of lights using Fresnel lenses that cause them to change colors at different viewing angles, providing visual cues to pilots as to whether their aircraft is on the correct (or incorrect) vertical path for an approach to a runway.

VDC: Volts, Direct Current

VDL: VHF Data Link

VDR: VHF Data Radio

VFE: Maximum flap extended speed

VFR: Visual Flight Rules (see VMC)

VG/DG: Vertical Gyro/Directional Gyro

VG: Vertical Gyro

VHF: Very High Frequency; 30-300 MHz, a “straight-line” signal used for communications and navigation.

VHSIC: Very High Speed Integrated Circuit

VIA: Versatile Integrated Avionics, offshoot of Integrated Modular Avionics.

VLF: Very Low Frequency, 3 KHz-30 KHz. Used for long range navigation in combination with Omega

VLSIC: Very Large Scale Integrated Circuit

VMC: Visual Meteorological Conditions (see VFR). Clear skies.

VNAV: Vertical Navigation

VNE: Never-exceed speed

VNO: Maximum structural cruising speed

VOR: VHF Omnidirectional Range

VORTAC: Combined VOR and Tacan system

VR: Rotation speed

VREF: Approach reference speed. The speed at which an aircraft is stabilized and flown during a landing approach.

VSI: Vertical Speed Indicator

VSI/TRA: Vertical Speed Indicator/Traffic, Resolution Advisory


WAAS: Wide area augmentation system. A series of differential GPS ground stations that broadcast correction information to airborne GPS receivers, allowing them to achieve a more accurate position determination.

WORM: Write-Once/Read Many. Optical disk technology.

WPT — waypoint:  A point in space used in navigation, generally an intersection of two airway routes

WS: Windshear

WX: Weather

WXR: Weather Radar


XPDR: Transponder

X/WIND — crosswind:  A wind blowing diagonally to the path of flight.

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