List_of_aviation,_aerospace_and_aeronautical_abbreviations

List of aviation, avionics, aerospace and aeronautical abbreviations

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Below are abbreviations used in aviation, avionics, aerospace and aeronautics.

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[McDonald_App_B-1] [1]
McDonald, Sandy A.F. From the ground up. Aviation Publishers Co. Ltd. pp. Appendix B.

[A&P_Technician_General_Textbook-2] [2]
Jeppesen, Boeing. A&P Technician General Textbook. pp. Glossary.

[3] [3]
"Definition of ACFT". www.merriam-webster.com. Retrieved 2023-05-11.

[4] [4]
FAA Airman Certification Standards

[Nielsen-5] [5]
Nielsen, Dane. PILOT PREP. Canuck West Holdings Inc.

[6] [6]
"Actual Off-Block Time - EUROCONTROL ATM Lexicon". ext.eurocontrol.int. Retrieved 2019-03-12.

[7] [7]
"AWWS – Forecasts and Observations". flightplanning.navcanada.ca. Retrieved 2017-04-06.

[8] [8]
"Airworthiness Directives".

[9] [9]
"Current rules". 17 February 2016.

[10] [10]
Aviation., Canada. Transport Canada. Canada. Civil (2005). Transport Canada aeronautical information manual : (TC AIM). Transport Canada. OCLC 1083332661.

[11] [11]
"CNS/ATM Systems" (PDF). International Civil Aviation Organization.

[12] [12]
"FAR/AIM Series". Aviation Supplies & Academics, Inc.

[13] [13]
"HFE".

[14] [14]
Canada, Environment and Climate Change (2012-05-23). "MANAB: Manual of Word Abbreviations - 4th edition". www.canada.ca. Retrieved 2022-09-12.

[15] [15]
Federal Aviation Administration, FAA. "What is a NOTAM?".

[16] [16]
"Training requirements". Civil Aviation Authority (UK).

[17] [17]
Wragg, David W. (1973). A Dictionary of Aviation (first ed.). Osprey. p. 218. ISBN 9780850451634.

[18] [18]
US DoD

[19] [19]
V&V – thefreedictionary.com

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[4]

[5]

[6]

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Abbreviation	Term	Notes
A/A	Air to air TACAN function
A/C	Aircraft^[1]
AC	Altocumulus	Cloud type
ACC	Altocumulus Castellanus	Cloud type
ACC	Area Control Centre
A/D	Aerodrome
A/F	Autofeather
A/FD	Airport/Facility Directory
A/P	Autopilot
AAE	Above aerodrome elevation^[1]	In aviation, above aerodrome level (AAL), or above aerodrome elevation (AAE), denotes that an altitude is given above the nearest aerodrome or airport.
AAIB	Air Accidents Investigation Branch	United Kingdom
AAIM	Aircraft Autonomous Integrity Monitoring
AAO	Assumed adverse obstacle
AAS	Airport advisory service^[1]
AC	Advisory circular^[2]	Information and guidance publication
ACAM	Aircraft continuous airworthiness monitoring
ACARS	Aircraft Communications Addressing and Reporting System
ACAS	Airborne collision avoidance system
ACC	Area control centre^[1]
ACC	Active clearance control	Turbine engine system
ACC	Accessory	In gas turbine engine
ACE	Actuator control electronics
ACFT	Aircraft^[3]
ACI	Airports Council International
ACLS	Automatic carrier landing system	Aircraft carrier operations
ACM	Air cycle machine	Part of A/C air conditioning system
ACMS	Aircraft condition monitoring system
ACP	Audio Control Panel
ACR	Avionic Communication Router
ACS¹	Airman Certification Standards^[4]	FAA pilot testing
ACS²	Audio control system
ACU¹	Air condition unit
ACU²	Alternator control unit^[2]	Protection from alternator over-voltage.
AD	Airworthiness Directive
ADA	Advisory area
ADAHRS	Air data attitude heading reference system
ADC	Air data computer
ADD	Acceptable deferred defect
ADF	Automatic direction finder	Navigation equipment
ADI	Attitude Director Indicator
ADIRS	Air Data Inertial Reference System
ADIRU	Air Data Inertial Reference Unit
ADIZ	Air defense identification zone
ADJ	Adjustment	Mechanical term
ADM¹	Aeronautical decision-making	Piloting term of judgment
ADM²	Air data module
ADN	Aircraft Data Network	Ethernet derivative for Commercial Aircraft
ADS¹	Air data system
ADS²	Automatic dependent surveillance
ADS-A	Automatic dependent surveillance – address
ADS-B	Automatic dependent surveillance – broadcast
ADS-C	Automatic dependent surveillance – contract
ADV	Arbeitsgemeinschaft Deutscher Verkehrsflughäfen	"German Airports Association"
AEA	Association of European Airlines
AESA	Active electronically scanned array
AFCS	automatic flight control system
AFD	Autopilot flight director
AFDC	Autopilot flight director computer
AFDS	Autopilot flight director system
AFDX	Avionics Full-Duplex Switched Ethernet
AFE	Above field elevation
AFIS	Airborne flight information system	Also called automatic flight information service
AFM	Aircraft flight manual
AFS	Aeronautical fixed service
AFT	Aft The direction against the aircraft movement
AFTN	Aeronautical Fixed Telecommunication Network
AGACS	Automatic ground–air communications system	Also known as ATCSS or data link
AGB	Accessory gear box	Mainly used in turbine engine
AGC	automatic gain control
AGDL	air–ground data link
AGL	above ground level
AHC	attitude heading control
AHRS	Attitude and heading reference system
AIDS	Aircraft integrated data system
AIM	Aeronautical Information Manual
AIP	Aeronautical Information Publication
AIRAC	Aeronautical information regulation and control
AIRMET	Air-mission's Meteorological Advisory^[5]	In-flight advisory given over 126.7
AIXM	Aeronautical information exchange model
ALC	Automatic level control
ALI	Airworthiness Limitation Item
ALNA	Airline network architecture
ALS	Approach lighting system
ALT¹	Alternate
ALT²	Altimeter
ALT³	Altitude
ALT hold	Altitude hold mode
ALTS	Altitude select
ALUM	Aluminum
AMC	Acceptable Means of Compliance (EASA)
AME	Aircraft Maintenance Engineer
AME	Aviation Medical Examiner
AMLCD	Active-matrix liquid-crystal display
AMM	Aircraft Maintenance Manual
AMO	Approved Maintenance Organization
AMS	Air management system
AMSL	Above mean sea level
AMP	Aircraft maintenance program
AMT	Aircraft Maintenance Technician
ANC	Active noise cancellation
AND	Aircraft Nose Down
ANN	Annunciator panel	Caution warning system normally containing visual and audio alerts to the pilot
ANPT	Aeronautical national pipe taper
ANR	Active noise reduction
ANSP¹	Air navigation service provider
ANSP²	Authorization of Aircraft Network Security Program (FAA)
ANT	Antenna (radio)
ANSOG	Airport Network Security Operator Guidance (Boeing)
A/O	Air oil	In turbine engines
AOA	Angle of attack
AOC¹	Air operator's certificate
AOC²	Aeronautical operational control
AOG	Aircraft on ground
AOM¹	Aircraft operations manual
AOM²	Airport/aerodrome operating minima
AOP	Airport operating plan
AP	Autopilot
A/P	Airplane (US), Aeroplane (ICAO)
APARS	Automatic pressure altitude reporting system
APC	Auto pilot computer
APIRS	Attitude and positioning inertial reference system
APOA	Airport of arrival
APOD	Airport of departure
APM	Aircraft personality module
APP	Appendix
APPL	Application
APPROX	Approximately
APS	Auto pilot system
APT	Airport
APU	Auxiliary power unit
APV	Approach procedure with vertical guidance	Instrumental approach
AQP	Advanced Qualification Program	FAA training and testing
AR	Airworthiness review
AR	authorization required
AR	As required
ARC	Airworthiness review certificate
ARINC	Aeronautical Radio Inc.
ARO	Airport reservation office
ARP	Aerodrome reference point
ARTCC	Air route traffic control centers
ASAS	Airborne Separation Assurance System
ASD	Aircraft situation display
ASDA	Accelerate Stop Distance Available
ASDL	Aeronautical satellite data link
ASI	Airspeed indicator
ASL	Above sea level^[1]
ASLO	Aircraft Security Logging Overview
ASM	Airspace management
ASM	Available seat miles
A-SMGCS	Advanced Surface Movement Guidance and Control System
assy	Assembly
A/S	Anti-Skid
ASR	Airport surveillance radar
ASU	Avionics switching unit
A/T	Autothrottle	Also 'AT'
A/THR	Autothrust
ATA	Air Transport Association
ATAG	Air Transport Action Group	A coalition of aviation industry experts focusing on sustainable development issues.
ATC	Air traffic control
ATCC	Air traffic control centre
ATCT	Airport traffic control tower
ATCRBS	Air traffic control radar beacon system
ATCSS	Air traffic control signalling system
ATD	Actual time of departure	Equivalent to off-block time^[6]
ATE	Advanced Technology Engine
ATF	Aerodrome traffic frequency
ATFM	Air traffic flow management
ATIS	Automatic Terminal Information Service
ATM	Air traffic management
ATN	Aeronautical Telecommunication Network
ATO	Approved Training Organisation
ATPL	Airline Transport Pilot Licence
ATQP	Alternative Training and Qualification Programme
ATR¹ ¹	Air transportable racking
ATR²	Automatic thrust restoration
ATS	Air traffic service
ATSAW	Airborne traffic situational awareness
ATSU	Air traffic services unit	Avionics LRU for ACARS
ATT	Attitude
ATTCS	Automatic Take-off Thrust Control System
AUPRTA	Airplane Upset Prevention & Recovery Training Aid
AVAIL	Available
Avionics	Aviation electronics
AVSA	"Adjust vertical speed adjust"	TCAS Voice command to adjust traffic separation
AWACS	Airborne Warning and Control System	Airborne early warning and control (AEW&C) or Boeing E-3 Sentry
AWBS	Aviation weather briefing service^[5]	Available at designated FSS's
AWG	American Wire Gage	The larger the size number, the smaller the wire diameter.
AWIS	Aviation weather information service^[5]	Available at FSS
AWO	All weather operations
AWOS	Automated weather observation system^[5]	Automated METAR reporting system
AWWS	Aviation weather web site^[7]	In Canada

Abbreviation	Term	Notes
B RNAV	Basic area navigation
BARO	Barometric indication, setting or pressure
baro-VNAV	Barometric vertical navigation
BC	back course	Or 'BCRS'
BCAA	Belgian Civil Aviation Authority
BDC	bottom dead centre^[1]	Piston engine
BDI	bearing distance indicator
BFL	balanced field length
BFR	biennial flight review
BGAN	Broadcast Global Area Network
BER	beyond economic repair	Hull loss
BHP	brake horsepower^[1]
BITE	Built-In Test Equipment
BL	Butt Line
BME	Bridge Mounted Equipment
B/P	Blue Print
BPR	bypass ratio
BOM	bill of material
BTV	Brake-to-Vacate System	A new feature introduced by Airbus A380
BWC	bird watch condition
BVID	Barely Visible Impact Damage
BVR	Beyond Visual Range

Abbreviation	Term	Notes
C2	command and control
CA	Captain
CAA	Civil Aviation Authority
CACTCS	Cabin Air Conditioning and Temperature Control System	(Pronounced "Cactus")
CAI	Caution Advisory Panel	Sometimes spelled "caution-advisory" or "caution/advisory". Also known as annunciator panel or Centralized Warning Panel (CWP)
CAM	cockpit area microphone	Part of a cockpit voice recorder
CAME	Continuing Airworthiness Management Exposition
CAMO	Continuing Airworthiness Management Organisation
CAMP	Continuous Airworthiness Maintenance Program (FAA)
CAN bus	Controller Area Network
CANSO	Civil Air Navigation Services Organisation
CAP	cabin attendant panel
CAR	civil aviation regulation
CARs	civil aviation regulations^[8]^[9]
CARS	Canadian Aviation Regulations
CAS	calibrated airspeed
CASS	Commercial Air Service Standards
CASS	continuing analysis and surveillance system
CAT (I–IIIc)	Operational performance Category	CAT I: Operational performance Category 1 CAT I Enhanced: Allows for lower minimums than CAT I in some cases to CAT 2 minimums CAT II: Operational performance Category II CAT IIIa: Operational performance Category IIIa CAT IIIb: Operational performance Category IIIb CAT IIIc: Operational performance Category IIIc
CAT¹	clear air turbulence^[1]
CAT²	Commercial Air Transport
CAVOK	Ceiling and Visibility OK^[10]	Visibility is at least 10 kilometres and no clouds below 5000 feet with no forecasted significant weather change such as precipitation.
CAVU	Ceiling and Visibility Unlimited
CAW	continuing airworthiness (EASA)
CB	Cumulonimbus cloud
CBT	computer-based training
CCRs	closed circuit mixed gas rebreathers
CCRs	constant current regulators
CDA	Continuous descent approach
CDCCL	critical design configuration control limitation
CDI	course deviation indicator
CDU	Control Display Unit
CDFA	Continuous Descent Final Approach
NUO
CDTI	Cockpit display of traffic information
CDL	configuration deviation list
CDU	control/display unit
CFIT	controlled flight into terrain
CFG	constant frequency generator
CFR	Code of Federal Regulations	In the United States
CG	center of gravity
CH	Course Heading
CHDO	certificate-holding district office (FAA)
CHP	Course Heading Panel
CHT	Cylinder Head Temperature (Piston engine aviation)
CI	cost index
CID	Customer induced damage
C/L	Centre line
CL	checklist	A flight deck manual, usually part of a Quick Reference Handbook
CLR	Clear	Seen on GFA and is used for sky coverage
CMC	central maintenance computer
CMM	component maintenance manual
CMO	Certificate Management Office	FAA
CMV	converted meteorological visibility
CMPA	complex motor-powered aircraft
CMU	Communications Management Unit
CNS	Communication, navigation and surveillance
CNS/ATM	Communication, navigation and surveillance / Air traffic management^[11]
CODEC	Coder/decoder
CofA	Certificate of airworthiness
COMM or COM	Communications transceiver, Communications receiver, or Communications radio transmitter	Now, normally: either VHF or UHF; HF communications avionics are usually abbreviated simply HF
CORSIA	Carbon Offsetting and Reduction Scheme for International Aviation
COTS	Commercial off-the-shelf
CPA	Closest point of approach
CPDLC	controller–pilot data link communications
CPR	Changed product rule	EASA
CPS	Cycles per second
CRD	Comment-response document (EASA)	Part of rule making process
CRES	Corrosion resistant steel
CRM	Crew resource management
CRT	Cathode ray tube
CS	certification specification (EASA)
CSD	constant speed drive
CSDB	Commercial Standard Digital Bus
CSDB	Collins Standard Digital Bus
CSN	Cycles since new	Normally measured in FC or EFC for an aircraft, engine or component
CSO	cycles since overhaul
CSS	cabin services system
CSU	constant speed unit
CSCT	Configuration Item Signer Crater Tool	Boeing
CTAF	common traffic advisory frequency
CTR	controlled traffic region/control zone
CV/DFDR	Cockpit voice and digital flight data recorder	See Flight recorder
CVR	cockpit voice recorder	See Flight recorder
CWS	control wheel steering

Abbreviation	Term	Notes
D	Compass Deviation
DA/H	decision altitude/height (rel. to THR)	See instrument landing system
DA¹	Decision Altitude	Precision approach or vertical guidance
DA²	density altitude
DA³	Drift angle
DAH	design approval holder (EASA)
DAPs	Downlink of aircraft parameters
DBER	damaged beyond economic repair	Hull loss
DCDU	Datalink control and display unit
DCL	Departure Clearance via CPDLC
DCP	Display control panel
DDG	Dispatch deviation guide	https://fsims.faa.gov/WDocs/8400.10%20Air%20Transp%20Ops%20Insp%20Handbk/Volume%204.%20AIRCRAFT%20EQUIPMENT%20AND%20OPERATIONAL%20AUTHORIZATIONS/Vol%204-Chap%204-Sec%203.htm
DEFDARS	Digital Expandable Flight Data Acquisition and Recording System
DER	departure end of runway
DER	Designated Engineering Representative
DEU	display electronic unit
DFDR	Digital Flight Data Recorder	See flight recorder
DFMC	Dual Frequency Multiple Constellation
DG	directional gyro
DGPS	differential GPS^[1]
DGR	Dangerous Goods Regulation
DH	Decision height	Precision approach, referred to threshold elevation
DIA	diameter
DLR	datalink recorder
DLR	German Aerospace Center / Deutsches Zentrum für Luft- und Raumfahrt e.V.
DME	distance measuring equipment
DME	Designated Mechanic Examiner^[2]	A person appointed by the FAA
DMI	deferred maintenance item
DNC	Direct noise canceling
DO	design organization
DOA	design organization approval	EASA
DODAR	diagnose, options, decide, act/assign, review
DOM	design organization manual
DOW	dry operational weight
DP	Departure Procedures
DPU	Display Processor Unit
DR	dead reckoning
DRMC	Direct Reading Magnetic Compass
DSP	Digital signal processing
DTO	declared training organisation
DTU	Data transfer unit
DUATS	Direct User Access Terminal Service
DVE	Degraded Visual Environment

Abbreviation	Term
EA	engineering authorisation
EADI	Electronic Attitude Direction Indicator
EAS	equivalent airspeed^[1]
EASA	European Aviation Safety Agency
EAT	expected approach time^[1]
EBOM	engineering Bill of Material
EBU	engine build-up
EC	engineering control (also E/C)
ECAM	electronic centralised aircraft monitor
ECET	end of civil evening twilight
ECR	Engineering Change Request
ECS	Environmental control system
ECU	Engine Control Unit (=EEC)
EDR	engineering data record
EDTO	extended diversion time operations
EEC	electronic engine control
EET	estimated elapsed time
EFB	electronic flight bag
EFC¹	Engine Flight Cycle
EFC²	expect further clearance
EFD	Electronic flight display
EFFRA	engine failure flap retraction altitude
EFIS	electronic flight instrument system
EFH	Engine Flight Hour
EFP	engine failure procedure
EFS	elevator feel shift
EFTO	engine failure on take-off
EFVS	Enhanced flight visual system
EGPWS	enhanced ground proximity warning system
EGI	Embedded GPS Inertial
EGNOS	European Geostationary Navigation Overlay Service
EGT	exhaust gas temperature
EHM	engine health monitoring
EHS	Enhanced surveillance
EHSI	Electronic Horizontal Situation Indicator
EICAS	engine-indicating and crew-alerting system
EIS	Electronic Instrument System
E-LSA	experimental light-sport aircraft
ELAC	elevator and aileron computer
ELOS	Equivalent Level of Safety
ELT	emergency locator transmitter
EMAS	engineered materials arresting system
EMDP	electric motor driven pump
ENC	Electronic noise canceling
ENCASIA	European Network of Civil Aviation Safety Investigation Authorities
ENG	engine
ENR	Electronic noise reduction
EOBT	estimated off-blocktime
EPA	European part approval (EASA)
EPR	engine pressure ratio
EPU	Emergency Power Unit
ERAM	En Route Automation Modernization
ERM	engineering request for maintenance
ESA	emergency safe altitude
ETA	estimated time of arrival
ETD	estimated time of departure^[1]
ETE	estimated time en route^[1]
ETL	effective translational lift
ETOPS	Extended-range Twin-engine Operation Performance Standards
ETSO	European Technical Standard Order, issued by EASA; see TSO
EUROCAE	European Organisation for Civil Aviation Equipment
EVAS	Emergency Vision Assurance System
EVSI	Enhanced Vision Systems Instrument
EVS	Enhanced Vision Systems
EW	Empty Weight

List_of_aviation,_aerospace_and_aeronautical_abbreviations

List of aviation, avionics, aerospace and aeronautical abbreviations

A

B

C

D

E

F

G

H

I

J

K

L

M

N

N numbers (turbines)

O

P

Q

R

S

T

U

V

V speeds

W

X

Y

Z

See also

References

External links

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Abbreviation	Term	Notes
FAA	Federal Aviation Administration	U.S. Department of Transportation agency
FAC	Final approach course
FACF	final approach course fix	Point at which the final approach descent is begun
FADEC	full authority digital engine control	Engine equipment
FAC	Flight Augmentation computer	Avionics
FAF	final approach fix
FAF	first available flight	Airline operations
FALS	full approach lighting system
FANS	Future Air Navigation System	Avionics
FAP	final approach point
FAP	forward attendant panel	Aircraft equipment
FAR	Federal Aviation Regulation	FAA regulation
FAR/AIM	Federal Aviation Regulation / Aeronautical Information Manual	Bundle of FAA regulations and Aeronautical Manual^[12]
FAROS	final approach runway occupancy signal
FAS	final approach segment
FAT	Free air temperature
FATO	final approach and take off
FB	Winds aloft	World Meteorological Organization abbrev. see also FD
FBO	fixed-base operator	Airfield operations
FBS	fixed base simulator	Flight crew training
FBW	fly-by-wire
FCC	Flight Control Computer
FC	flight crew
FCF	functional flight check	Check functionality after maintenance
FCMC	Fuel Control & Monitoring Computer
FCOM	flight crew operating manual	Aircraft operations
FCS	flight control system
FCTM	flight crew training manual
FCU	fuel control unit	In turbine engines
FD	flight director	Avionics
FD	upper winds and temperature forecast^[1]	US and Canada abbrev. See also FB
FDAU	flight-data acquisition unit
FDM	flight data monitoring	Operations planning
FDP	flight duty period
FDPS	flight plan data processing system	Flight planning
FDR	flight data recorder	Avionics. Also known as 'black box'.
FDRS	flight data recorder system	Avionics
FDTL	flight duty time limitations
FDU	flux detector unit
FEP	final end point
FF	fuel flow
FFDZ	free fall drop zone (parachutists)
FFS	full flight simulator	Flight crew training
FG	Flight Guidance
FIC	flight information centre
FIDO	Fog Investigation and Dispersal Operation	Airfield operations
FIKI	Flight Into Known Icing	Aircraft operations
FIR	flight information region	ATC
FIS	Federal Inspection Services
FIS-B	Flight information services – broadcast
FISE	flight information service enroute
FL	flight level	ATC
FLIR	Forward-looking infra-red
FLTA	Forward-looking terrain avoidance
FM	frequency modulation	Example: FM immunity
FMA	flight mode annunciator	Equipment
FMC	flight management computer (part of a FMS)	Avionics
FMGC	Flight management and guidance computer	Avionics. Also FMGS: Flight Management & Guidance System
FMS	flight management system	Avionics
FO	first officer	Flight crew
FOB	Fuel On-Board
FOD	foreign object damage	Airfield operations
FOO	flight operations officer	Airline employee
FOQA	flight operational quality assurance
FPA	flight path angle
FPL	filed flight plan	ATC
FPM	feet per minute
FQIS	Fuel Quantity Indication System
FREQ	Frequency
FSDO	Flight Standards District Office (FAA)
FSF	Flight Safety Foundation	U.S.-based nonprofit organisation
FSIMS	Flight Standards Information Management System (FAA)
FSS	flight service station
FTD	flight training device	Flight crew training
FTL	flight time limitations
FVU	flux valve unit	Equipment
FWS	Flight warning system
FYDS	Flight director / yaw damper system

Abbreviation	Term	Notes
GA	general aviation
G/A or GA	go-around	Aborted landing procedure
GAST	GBAS Approach Service Type
GBAS	Ground based augmentation system
GCAS	Ground collision avoidance system
GBST	ground-based, software tool	Airfield operations
GCA	Ground-controlled approach	Airfield operations
GCU	generator control unit
GDOP	Geometric dilution of precision
GEA	Ground effect area
GGS	Global positioning system ground station
GHz	Gigahertz
GLOC	g-induced loss of consciousness	"g" Is acceleration relevant to the acceleration caused by gravity
GLONASS	Global Navigation Satellite System	Or GNSS
GLNS	GPS Landing and Navigation System
GLNU	GPS Landing and Navigation Unit
GLS	GBAS Landing System
GLU	GPS landing unit
GM	guidance material (EASA)
GMM	general maintenance manual
GMT	Greenwich Mean Time
GND	ground	Airfield operations
GP	glide path	See instrument landing system
GPP	general practices and procedures
GPS	Global Positioning System	Avionics
GPU	Ground Power Unit	Aerospace Ground Equipment
GPWS	ground proximity warning system	Avionics
G/S	glideslope	Avionics
GS	groundspeed
GSE	ground support equipment	Aerospace ground equipment
GSPT	Gross shop processing time
GUMPS	Gas, Undercarriage, Mixture, Propeller, Seat belts/Switches	Mental checklist before landing

Abbreviation	Term	Notes
H	Heavy	Wake turbulence category
H	High
HAA	Height above airport
HAT	Height Above Touchdown
HAZMAT	Hazardous Material
HBCS	High Bandwidth Connectivity System
HDB	Horizontal Deviation Bar (GS)
HDG	Heading	Navigation
HDG SEL	Heading select	Navigation
HDI	Horizontal Deviation Indicator
HDOP	Horizontal dilution of precision
HF	High frequency
HFE	Human Factors Engineering^[13]
HFES	Human Factors and Ergonomics Society	U.S.-based nonprofit organisation
"Hg	Inch of Mercury	Symbol for unit of pressure
HHLD	Heading hold	Navigation
HIGE	hover in ground effect	Helicopter operations
HIRL	High Intensity Runway lighting	Airfield operations
HIRO	High Intensity Runway Operation	Airfield operations
HIRTA	High Intensity Radio Transmission Area
HIWAS	Hazardous Inflight Weather Advisory Service
HL	Height loss
HLD	hold	Maintain same altitude or speed or direction
HMG	hydraulic motor generator
HMD	Helmet-mounted display
HMU	hydro-mechanical unit	In turbine engine
HOGE	hover out of ground effect	Helicopter operations
HOTAS	Hands On Throttle And Stick
HPA	human-powered aircraft	Aircraft type
HPC	high pressure compressor	In turbine engine
HPR	High Pressure Rotor
HPT	high pressure turbine	In turbine engines
HPTACC	high pressure turbine active clearance control	Mainly used in turbofan engines
HSD	High-speed data
HSI	horizontal situation indicator	Avionics
HSL	Heading select
HUD	head-up display	Avionics
HUM	Human Remains
HUMS	Health and usage monitoring systems
HW	headwind
HYD	hydraulic	Aircraft equipment
HYDIM	hydraulic interface module
Hz	Hertz	Symbol for unit of frequency

Abbreviation	Term	Notes
IAC	instrument approach chart
IAF	initial approach fix
IAN	Integrated Approach Navigation	IAN approaches provide the functions, indications and alerting features similar to an ILS approach (B737 FCTM)
IAP	instrument approach procedure
IAS	indicated airspeed
IATA	International Air Transport Association
IB	inboard
ICA	Instructions for Continuous Airworthiness
ICAO	International Civil Aviation Organization
ICAS	International Council of the Aeronautical Sciences
ICD	interface control document
ICO	idle cut-off
ICTS	ice-contaminated tailplane stall
ID	identify/identification or identifier
IDENT	identify/identifier
IDG	integrated drive generator	Combination of a CSD and generator in a single case
IDS	information display system	Or: integrated display system
IDT	identify	XPDR
IEPR	integrated engine pressure ratio
IETM	interactive electronic technical manual
IF	intermediate approach fix	Instrumental approach
IFA	International Federation of Airworthiness
IFATCA	International Federation of Air Traffic Controllers' Associations
IFE	in-flight entertainment
IFF	identification friend or foe
IFICS	integrated flight instrument and control system	British Aircraft Corporation, now British Aerospace
IFP	instrument flight procedure
IFR	instrument flight rules
IFSD	in-flight shutdown
IGV	inlet guide vane
ILS	instrument landing system
IMC	instrument meteorological conditions
IML	inside mold line
IND	indicator
InHg	inch of mercury
INS	inertial navigation system
IPC	illustrated parts catalog (e.g. by Boeing, Airbus)
IR	initial release
IRS	inertial reference system
IRT	instrument rating test
IRU	inertial reference unit
IRVR	instrumented runway visual range
ISA	International Standard Atmosphere
ISFD	integrated standby flight display
ISIS	integrated standby instrument system
ISP	integrated switching panel
ITAR	International Traffic in Arms Regulations
ITT	interstage turbine temperature
IVSI	instantaneous vertical speed indicator

Abbreviation	Term
JAA	Joint Aviation Authorities
JAR	Joint Aviation Requirements
JTIDS	Joint Tactical Information Distribution System

Abbreviation	Term
KCAS	knots calibrated airspeed
KIAS	knots indicated airspeed
KRE	key risk element
KTAS	knots true airspeed

Abbreviation	Term	Notes
L	Light	Wake turbulence category
LAAS	Local Area Augmentation System
LADGPS	Local Area Differential GPS
LAHSO	Land And Hold Short Operations
LAME	licensed aircraft maintenance engineer
LAT	large air tanker	A class of waterbomber
LCC	low-cost carrier
LCD	liquid crystal display
LCG	load classification group
LCN	load classification number
LDA	landing distance available
LDA	localizer type directional aid
LDGPS	local area differential global positioning satellite
LDR	landing distance required
LED	light-emitting diode
LHO	live human organs
LHS	left hand seat	Jargon for captain
LIR	Loading Instruction Report
LKP	last known position
LLC	Life Limited Component
LLP	Life Limited Part	EASA, ICAO
LLZ	localizer	ILS approach
LM	land and marine
LMM	Locator middle marker
LNAV	lateral navigation
LOA	letter of authorization	FAA
LOC	localizer
LOC	loss of control
LOCI	loss of control inflight
LOFT	line-oriented flight training
LOM	limitation of movement
LOM	locator outer marker
LOPA	Location of Passenger Accommodations
LORAN	Long-range navigation
LOTC	loss of thrust control
LPC	low pressure compressor	In turbine engines
LPR	Low Pressure Rotor
LPT	low pressure turbine
LPTACC	low pressure turbine active clearance control	Mainly used in turbofan engines
LPV	localizer performance with vertical guidance
LRC	long range cruise
LRU	line-replaceable unit
LSAP	loadable software aircraft part (EASA)	Introduced in RMP for technical records
LSAS	longitudinal stability augmentation system
LTC	line training captain
LTE	Loss of Tail Rotor Effectiveness	Helicopters
LTP	landing threshold point
LVP	low visibility procedures	Designated state of operations at aerodromes where instrument approaches and low-visibility takeoff procedures are used during inclement weather
LW	landing weight
LX	Lightning
LZ	landing zone

Abbreviation	Term	Notes
M	medium	Wake turbulence category
MAC	mean aerodynamic chord
MAC	mid-air collision
MAHF	Missed Approach Holding Fix	Used in RNAV
MANAB	Manual of Word Abbreviations^[14]	Used in Canada
MAP	manifold absolute pressure
MAP	missed approach point	Or: MAPt. Instrument approach.
MAPS	Minimum Aviation Performance Standards
MATS	Manual of Air Traffic Services
MB	Marker beacon
MBC	Main Base Check
MCAS	Maneuvering Characteristics Augmentation System	Held responsible for Boeing 737 MAX groundings
MCBF	Mean cycles between failures
MCC	Multi-crew cooperation
MCDU	multifunction control display unit
MCH	Manufacturer Certificate Holder	TCCA; see also PAH and POA
MCP	mode control panel
MCT	maximum continuous thrust
MCDU	multi control display unit
MDA	minimum descent altitude	Or: minimum decision altitude. Non-precision approach.
MDDR	maintenance deferred defect record
MDH	minimum descent height	Or: minimum decision height. Non-precision approach.
MDM	multi-disciplinary measure	EASA
ME	Manufacturing Engineer
MEA	Minimum En-route Altitude
MEDEVAC	medical evacuation
MEF	maximum elevation figure
MMEL	master minimum equipment list
MEL	minimum equipment list
MEP	multi-engine piston
METAR	meteorological aerodrome report
MF	Medium frequency
MFD	multi-function display
MFDS	multi-function display system
MFRA	minimum flap retraction altitude
MH	magnetic heading
MIC	Microphone
MIDS	Multifunctional information distribution system
MILSPEC	Military specification
MKP	Multi-function Keypad
MKR	Marker beacon
ML	maintenance laptop
MLDW	maximum landing weight
MLG	Main Landing Gear
MLS	microwave landing system
MM	middle marker
MMD	Moving map display
MNPS	Minimum navigation performance specifications
MOA	Military operations area
MOCA	Minimum Obstacle Clearance Altitude
Mode A	Transponder pulse-code reporting
Mode B	Transponder code and altitude reporting
Mode C	Transponder code, altitude, and TCAS reporting
MOE	maintenance organisation exposition
MOPS	Minimum Operational Performance Standard
MORA	Minimum Off Route Altitude
MOSArt	Modular Open System Architecture
MP	manifold pressure
MPL	multi-crew pilot license
MPU	Multifunction Processor Unit
MRB	Material Review Board
MRO	maintenance, repair, overhaul
MRO	maintenance and repair organization
MROT	Minimum Runway Occupancy Time
MRP	Material Resources Planning
MRW	maximum ramp weight
MSA	minimum safe altitude / minimum sector altitude
MSD	Minimum Stabilization Distance
MSDS	Material Safety Data Sheet
MSG	Message
MSL	mean sea level
MSLW	Max. Structural Landing Weight
MSP	Modes S-Specific Protocol
MSSS	Mode S-Specific Services
MSTOW	Max. Structural Take-off Weight
MSZFW	Max. Structural Zero Fuel Weight
MTBF	Mean time between failures
MTBSV	Mean time between shop visit
MTBUR	Mean time between unscheduled removals
MTOW	maximum take-off weight
MTTF	Mean time to failure
MVA	Minimum Vectoring Altitude
MVFR	Marginal visual flight rules
MX	Maintenance
MZFW	Maximum Zero Fuel Weight

Abbreviation	Term	Notes
NADP	noise abatement departure procedure
NAS	National Airspace System	United States
NAV	Navigation receiver	Normally VHF navigation receiver for VOR
Navaid	Navigational aid	Or: aid to navigation (ATON)
NAVCOMM	Combination navigation and communications equipment	Or: NAV/COM or NAV-COM. normally VHF navigation receiver integrated with VHF communications transceiver
NAVSTAR-GPS	Navigation Satellite Timing And Ranging	The space-borne or satellite navigation system
NCAT	National Center for Aviation Training	US educational facility
NCATT	National Center for Aircraft Technician Training	US educational facility
ND	Navigation display
NDB	non-directional beacon
NDT	non-destructive testing
NFF	No fault found	Or: no trouble found (NTF) or no defect found (NDF)
NGS	nitrogen generation system
NHA	next higher assembly
NIST	National Institute of Standards and Technology
NLG	nose landing gear
NLR	Netherlands Aerospace Research Centre
NM	Nautical mile	Or: NMI
NNC	non-normal checklist
NNM	non-normal maneuver (Boeing QRH - 737 Flight Crew Operations Manual)
NORAD	North American Aerospace Defense Command	US-Canadian military security agency
NORDO	no radio
NOTAM	Notice to air missions^[15]
NOTAR	no tail rotor^[2]	Helicopter control system
NOZ	Normal Operating Zone	Parallel runways operation
NPA	non-precision approach	Instrumental approach
NPA	notice of proposed amendment	EASA
NPRM	notice of proposed rulemaking	FAA
NRR	noise reduction rating	hearing protector attenuation
NRTC	nonroutine task card
NVD	Night-vision device	Or: Night-vision goggles (NVG)
NTSB	National Transportation Safety Board	U.S. governmental agency
NTZ	no-transgression zone	Parallel runways operation

Abbreviation	Term	Notes
N_#	compressor speed^[1]	N₁, N₂, etc. refers to the specific compressor spool (in the order that air passes over them). (See: Jet engine)
N_g	gas generator speed^[1]
N_h	high rotor speed^[1]
N_p	power turbine speed^[1]
N_r	rotor speed (helicopters)	Np and Nr are typically shown on the same gauge with two needles, both expressed in percent, so that the pilot can tell if the power turbine is driving the rotor or if it is freewheeling.

Abbreviation	Term	Notes
P	(as a prefix:) prohibited airspace
PA	pressure altitude
PA	Public address system
PAEW	Personnel and equipment working
PAH	production approval holder	FAA; see also POA and MCH
PAL	Pilot Activated Lighting
PANS-OPS	procedures for air navigation services – aircraft operations
PAOG	Pre Aircraft on Ground
PAPI	precision approach path indicator
PAR	precision approach radar
PATWAS	Pilot's Automatic Telephone Weather Answering Service^[5]
PAX	passenger
PBCS	performance-based communication and surveillance
PBD	place bearing distance	RNAV waypoint
PBE	Protective Breathing Equipment
PBN	Performance-Based Navigation
PC	proficiency check
PCL	Pilot Controlled Lighting
P-Code	GPS precision code
PCN	pavement classification number
PD	Profile descent
PDA	performance degradation allowance
PDAS	public domain aeronautical software
PDC	Pre-Departure Clearance
PDG	procedure design gradient
PDM	pilot decision making
PDOP	Position dilution of precision
PDU	power drive unit	Flap actuation
PET	point of equal time
PESA	Passive electronically scanned array
PF	pilot flying
PFAF	precision final approach fix
PFD	primary flight display	Or: primary flight director
PIC	Pilot In Command
PICUS	Pilot In Command, under supervision^[16]
PIO	Pilot Induced Oscillations
PIP	performance improvement package
PIREP	Pilot Report
PJA	Parachute Jumping Area
PJE	Parachute jumping exercise

Abbreviation	Term	Notes
QAR	quick access recorder
QCM	quality and compliance monitoring
QEC	quick engine change
QFE	the Q-code for: Atmospheric pressure at aerodrome elevation (or at runway threshold)
QNE	the Q-code for pressure altitude
QNH	the Q-code for: Altimeter sub-scale setting to obtain elevation when on the ground, i.e. altitude above MSL
QRA	quick reaction alert
QRH	quick reference handbook
QTOL	quiet take-off and landing^[17]

Abbreviation	Term	Notes
R	(as a prefix:) restricted airspace
RA	radio altitude or radar altimeter
RA	resolution advisory	In the context of TCAS
RAAS	Runway Awareness and Advisory System
RAAS	remote airport advisory service
Rad Alt	Radio Altitude
Radar	RAdio Detection And Ranging
RAI	Radio altimeter indicator
RAIM	Receiver Autonomous Integrity Monitoring	Or: remote autonomous integrity monitoring
RALT	Radar or radio altimeter
RAREPS	Weather Radar Reports^[5]	Provided by Air Traffic Controllers
RAS	rectified air speed
RA(T)	restricted area (temporary)
RAT	ram air turbine
RCO	remote communications outlet
RCR	Reverse current relay
RCVR	Radio receiver
RDH	reference datum height	For instrument landing system (ILS)
RDMI	Radio distance magnetic indicator
RDP	Radar data processing system
RDR	Radar
REF	Reference
REIL	Runway end identifier lights
REL	Relative
REO	Repair engineering order
RESA	runway end safety area
RF	Radio frequency
RFF	rescue and fire fighting
RFI	Radio frequency interference
RFI	recreational flight instructor
RGB	reduction gear box
RHS	right hand seat	Jargon for first officer
RHSM	reduced horizontal separation minimal
RIA	regulatory impact assessment (EASA)
RII	required inspection items
RLG	Ring laser gyroscope
RLTC	Remaining Life Time Cycle	Counter to the limiter especially for LLPs in engines
RLY	Relay
RMI	radio magnetic indicator
RMP	Radio Management Panel

Abbreviation	Term	Notes
SAF	Sustainable aviation fuel
SAIL	Specific assurance and integrity level
SAR	Search and rescue
SAR	Smart ACMS Recorder
SAR	Surveillance Approach Radar
SAS	stability augmentation system
SAT	Static Air Temperature	Or: Outside air temperature (OAT)
SATCOM	Satellite communication
SATNAV	Satellite navigation
SB	service bulletin
SBAAS	Satellite-Based Augmentation System	Or: SBAS
SC	special condition
SCAP	Standard Computerized Airplane Performance
SCCM	senior cabin crew member
SD	Secure digital
SDF	Simplified directional facility
SDU	Satellite data unit
SELCAL	Selective calling
SEP	Safety and Emergency Procedures
SEP	single-engine piston
SESAR	Single European Sky ATM Research
SESMA	Special Event Search and Master Analysis
SF	Stratus Fractus	Cloud type
SFCC	Slat Flap Control Computer
SFO	Senior First Officer
SFP	Short Field Performance	B737 Enhancement program for landing in short runways
SFOC	Special Flight Operating Certificate
SID	standard instrument departure
SIGMET	Significant Meteorological Information
SIU	Satellite interface unit
SLPC	single lever power control
SM	service manual
SMM	safety management document	ICAO
SMOH	Since major overhaul
SMR	surface movement radar
SMS	Short Messaging Service
SMT	software maintenance tool
SN	serial number
SNR	signal-to-noise ratio
SOC	start of climb at missed approach

Abbreviation	Term	Notes
OAS	Obstacle Assessment Surface
OAT	outside air temperature
OBE	overcome by events
OBI	Omnibearing indicator	See CDI
OBS	omni-bearing selector
OCA	obstacle clearance altitude
OCC	Operations control center
OCCM	on condition / condition monitored components
OCH	obstacle clearance height
OEI	one engine inoperative
OEM	original equipment manufacturer
OFZ	Obstacle Free Zone
OGV	outlet guide vane
OHM	overhaul manual
OIS	obstacle identification surface	Instrumental procedures
OIS	Operational Information System
OM	outer marker
OML	outer mold line
ONS	onboard network system
ONAT	Onboard Network Access Terminal
O/R	On Request
OTS	out of service
OPC	operational check
OPS/CHK	operational check
OW	operational weight
OWE/OEW	Operating Weight Empty/Operating empty weight

Abbreviation	Term	Notes
TA	traffic advisory	See TCAS
TAA	terminal arrival altitude
TAA	terminal arrival area
TAC	thrust asymmetry compensation
TACAN	tactical air navigation (system)
Tach	Tachometer
TAD	Terrain awareness display
TAF	terminal aerodrome forecast	Or: Terminal area forecast.
TAI	thermal anti-ice
TALPA	Takeoff and Landing Performance Assessment Aviation Rules Committee
TAM	total airport management
TAR	terminal approach radar
TAS	true airspeed
TAT	total air temperature	Or: true air temperature
TAWS	terrain awareness and warning system
TBO	time between overhauls	Or: time before overhaul
TBV	transient bleed valve	In turbine engines
TC	Transport Canada
TC	towering cumulus
TC	turn coordinator
TC	True Course
TC	type certificate
TCA	terminal control area (USA/Canada)	Europe: terminal manoeuvring area (TMA)
TCA	Throttle control assembly
TCAS	traffic collision avoidance system
TCCA	Transport Canada's Civil Aviation
TCDS	type certificate data sheet
TCF	Terrain clearance floor
TCH	threshold crossing height
TCI	thrust computer indicator
TCN	TACAN
TCU	Telecommunication control unit	Or: terminal control unit, or line control unit, used in Air traffic control
TDOP	Time dilution of precision
TDR	Transponder	(In some cases)
TDZ	touchdown zone
TERPS	terminal instrument procedures	Or: terminal en route procedures
TFC	traffic
TFR	temporary flight restriction	Airspace
TFT	Thin-film transistor
TGB	transfer gearbox
TGL	temporary guidance leaflet
TGL(S)	touch-and-go landing(s)
TGT	Target
TGT	Turbine gas temperature
THLD	threshold	Or: THR
TH	True Heading	Or: THDG
THR	runway threshold
THS	trimmable horizontal stabilizer, see tailplane
TIS–B	Traffic information service – broadcast
TIT	turbine inlet temperature
TK	Track angle
TKE	Track-angle error
TLD	time-limited dispatch
TLA	Three-letter acronym
TLA	Thrust lever angle
TLB	technical logbook (EASA)
TLS	transponder landing system
TMA	terminal manoeuvring area (Europe)	USA/Canada: terminal control area
TMG	touring motor glider
TML	Toolbox Mobile Library (Boeing)
TMZ	transponder mandatory zone
TOC	Top of climb	Or: T/C
TOD	top of descent (point)	Or: T/D
TODA	take-off distance available
TO/GA	Takeoff/go-around switch / thrust	Or: TOGA
TOP	take-off power
TOR	take-off runway
TORA	take-off runway available
TOT	Turbine outlet temperature
TOW	take-off weight
TOWS	take-off warning system
TR	tail rotor	Or: T/R. Helicopters.
TR	thrust reverser(s)	Or: T/R
TR	transformer rectifier
TR	transmitter receiver or transceiver	Or: T/R
TP	turning point at missed approach
TRA	temporary reserved area (airspace)
TRACON	terminal radar approach control
TRANS	transition
TRANS	Transmission (telecommunications)	Or: transmit
TRE	type rating examiner
TRK	Track
TRP	thrust rating panel
TRP	Mode S transponder
TSO	technical standard order^[2]	FAA specification of quality standard.
TSLOVH	Time since last overhaul	Normally measured in FH or EFH
TSN	Time since new	Normally measured in FH or EFH for an aircraft, engine or component
TTAF	total time air frame
TTL	Tuned to Localizer
TTR	TCAS II transmitter/receiver
TTS	Time to station
TTSN	total time since new
TTSO	total time since overhaul
TVE	Total vertical error
TWB	Transcribed Weather Broadcasts^[5]	Abbreviated area forecast
TWC	tail wind component
TWDL	Two-way data link	Or: terminal weather data link
TWDR	Terminal Doppler Weather Radar
TWIP	Terminal weather information for pilots
TWLU	Terminal Wireless LAN Unit
TWR	Air traffic control tower
TWR	Terminal weather radar
TWY	taxiway
TX	Transmit

Abbreviation	Term	Notes
UAC	Upper area control
UART	Universal asynchronous receiver-transmitter
UAS	Unmanned Aircraft System^[18]
UAV	Unmanned aerial vehicle	Commonly called 'drones', also 'Remotely Piloted Aircraft (RPA)'
UHF	ultra-high frequency
UIR	upper information region
ULB	underwater locator beacon
UNL	Unlimited	Seen on GFA and is used for visibility
UPRT	upset prevention and recovery training
USB	Universal Serial Bus
UTC	Universal Time Coordinated	Indicates time zones

Abbreviation	Term	Notes
V	magnetic variation
V	Volts or voltage
V&V	video & vision^[19]
VAR	Variation
VASI	visual approach slope indicator	VASIS = visual approach slope indicator system
VBV	variable bleed valve	In turbine engines
VCR	visual control room
VCS	vehicle control service
VDF	VHF direction-finding
VDL	VHF Data Link
VDP	visual descent point	Point in a direct approach where a 3º normal visual descent can be started to achieve a safe landing and stabilized approach to the RWY - VDP (in distance) = HAT (height over terrain) / 300 (HAT is the height of the MDA read in the approach chart of the AD)
VDR	VHF digital radio
VFO	Variable-frequency oscillator
VFR	visual flight rules
VG	vortex generator
VGA	Video Graphics Array
VG/DG	Vertical gyroscope/directional gyroscope
VGLS	Visual Guidance Lighting Systems	FAA navigation services
VGM	voice generator module	See AWOS
VHF	very high frequency
VID	visible impact damage
VIGV	variable inlet guide vane
V/L	VOR/Localizer
VMC	visual meteorological conditions
VMC	minimum control speed with critical engine out
VNAV	vertical navigation	Or: V/NAV
VNC	VFR navigation chart
VNE	Never exceed speed
VNO	Maximum structural cruising speed
VNR	VHF navigation receiver
VOR	VHF omni-directional range
VOR/DME	VOR with Distance measuring equipment
VOR/MB	VOR marker beacon
VORTAC	VOR and TACAN combination
VOX	Voice transmission	Voice Operated Transmitter
VPA	Vertical Path Approach
VPATH	Vertical path
V/R	Voltage regulator
VRP	Visual point of reference
VRS	vortex ring state	Helicopter flight phenomenon
V/S	Vertical speed
VSCF	variable speed constant frequency	Electricity generation system
VSI	vertical speed indicator
VSM	Vertical separation limit
VSO	Stall speed in landing configuration
VSV	variable stator vane	In a turbine engine
VSWR	Voltage–standing wave ratio
VTA	VFR terminal area chart^[1]
VTOL	vertical take-off and landing^[1]
V/TRK	Vertical track
VVI	vertical velocity indicator	Same as VSI
VX	Speed for best angle of climb
VY	Speed for best rate of climb

Abbreviation	Term	Notes
WAAS	Wide Area Augmentation System
WAC	World Aeronautical Chart
WAT	weight, altitude, temperature	Variables that affect takeoff performance
W&B	Weight & Balance	Sometimes referred to as WxB
WCA	Wind Correction Angle
WD	Wind direction	Or: WINDR
WDM	Wiring Diagram Manual
WEF	with effect from
WEP	War Emergency Power
WMA	WXR waveguide adapter
WMI	WXR indicator mount
WMS	Wide-area master station
WMSC	Weather message switching center
WMSCR	Weather message switching center replacement
WOCL	window of circadian low
WOFW	weight-off-wheels	Indicates aircraft is off ground since lift off
WONW	weight-on-wheels	Indicates aircraft is on ground since touch down
WPT	Waypoint	Or: WYPT
WRT	WXR receiver transmitter
WS	wind shear
WTC	Wake Turbulence Category
Wx	weather^[1]
WXR	Weather radar system

Abbreviation	Term	Notes
XC	cross-country^[1]
XCVR	Transceiver
XFR	Transfer
XMIT	transmit
XMSN	transmission
XMTR	transmitter
XPDR	transponder
XPNDR	transponder
XTK	Crosstrack
X-Start	Cross-start	Using the air pressure or electrical power from a working engine

Abbreviation	Term	Notes
Z	Zulu Time	Coordinated Universal Time (UTC)
ZFT	zero-fuel time
ZFW	zero-fuel weight
ZULU	Zulu Time	Coordinated Universal Time (UTC)