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ReferenceAviation Glossary

Aviation glossary: every term you need to know

100+ aviation terms, acronyms, and abbreviations used in FAA regulations, weather products, ATC communications, and pilot training. Bookmark this page for quick reference.

A

ACS
Airman Certification Standards. The FAA document that defines the knowledge, risk management, and skill standards for each pilot certificate and rating. Replaced the PTS for most certificates.
AD
Airworthiness Directive. A legally enforceable regulation issued by the FAA to correct an unsafe condition in an aircraft, engine, propeller, or appliance.
ADF
Automatic Direction Finder. A radio navigation instrument that determines the bearing to a non-directional beacon (NDB) relative to the aircraft heading.
ADIZ
Air Defense Identification Zone. Airspace within which the identification, location, and control of aircraft is required in the interest of national security.
ADS-B
Automatic Dependent Surveillance-Broadcast. A surveillance technology where aircraft determine their position via GPS and broadcast it to ground stations and other aircraft. ADS-B Out is required in most controlled airspace since January 2020.
AFM
Aircraft Flight Manual. The FAA-approved document that contains the operating limitations, procedures, performance data, and weight and balance information for a specific aircraft.
AFSS
Automated Flight Service Station. A facility that provides preflight briefings, en-route weather, NOTAMs, and flight plan services to pilots. Accessible via 1-800-WX-BRIEF.
AGL
Above Ground Level. Altitude measured from the surface directly below the aircraft. Cloud heights in METARs and traffic pattern altitudes are reported in AGL.
AHRS
Attitude and Heading Reference System. A sensor system that provides aircraft attitude (pitch and roll) and heading information to electronic flight displays.
AIRMET
Airman's Meteorological Information. An advisory for weather conditions that may affect aircraft safety, particularly for lighter aircraft. Covers moderate icing, moderate turbulence, sustained surface winds of 30+ knots, and IFR conditions.
ATC
Air Traffic Control. The ground-based service that directs aircraft movement on the ground and in the air to maintain safe separation and orderly flow of traffic.
ATIS
Automatic Terminal Information Service. A continuous broadcast of recorded non-control aerodrome information at busier airports. Updated hourly or when conditions change, identified by phonetic letter.
ATP
Airline Transport Pilot. The highest level of pilot certificate issued by the FAA. Required for Part 121 airline operations. Minimum 1,500 hours total time (with limited exceptions).

B

BasicMed
A medical qualification alternative to a traditional FAA medical certificate. Requires a physical exam by a personal physician every 48 months and an online medical education course every 24 months. Limited to aircraft under 6,000 lbs with no more than 6 seats.
BFR
Biennial Flight Review. Now formally called a Flight Review under 14 CFR 61.56. Requires at least 1 hour of ground training and 1 hour of flight training with a CFI every 24 calendar months to maintain pilot privileges.

C

CFIT
Controlled Flight Into Terrain. An accident where an airworthy aircraft under pilot control is unintentionally flown into the ground, water, or an obstacle. A leading cause of fatal GA accidents, often related to VFR flight into IMC.
CFI
Certificated Flight Instructor. A pilot who holds a flight instructor certificate and is authorized to provide flight and ground training. CFIs provide the endorsements required for solo flight, knowledge tests, and practical tests.
CFII
Certificated Flight Instructor — Instrument. A CFI who also holds an instrument instructor rating and is authorized to provide instrument flight training.
CG
Center of Gravity. The point at which the aircraft would balance if suspended. Must remain within the approved envelope throughout all phases of flight for safe operation.
Class A Airspace
Airspace from 18,000 feet MSL up to and including FL600. IFR flight only. ATC clearance required. All aircraft must be on an IFR flight plan and equipped with a Mode C transponder.
Class B Airspace
Airspace surrounding the busiest airports (e.g., major airline hubs). Resembles an upside-down wedding cake. ATC clearance required for all aircraft. Mode C transponder and ADS-B Out required.
Class C Airspace
Airspace surrounding airports with an operational control tower, radar approach control, and a minimum level of IFR or passenger operations. Two-way radio communication required. Mode C transponder required within and above.
Class D Airspace
Airspace surrounding airports with an operational control tower. Typically extends from the surface to 2,500 feet AGL. Two-way radio communication required. No transponder requirement (unless in a Mode C veil).
Class E Airspace
Controlled airspace that is not Class A, B, C, or D. Encompasses most of the airspace above 1,200 feet AGL in the continental US. No ATC communication requirement for VFR flight, but IFR flights require ATC clearance.
Class G Airspace
Uncontrolled airspace. ATC has no authority or responsibility to control air traffic. Exists primarily below 1,200 feet AGL in areas not designated as Class B, C, D, or surface-based Class E.
CPL
Commercial Pilot License/Certificate. Authorizes the holder to act as PIC of an aircraft for compensation or hire. Requires minimum 250 hours total time under Part 61.
CRM
Crew Resource Management. A systematic approach to optimizing the use of all available resources — people, equipment, and information — to achieve safe and efficient flight operations. Originally developed for airline crews, now applied to all aviation.
CTAF
Common Traffic Advisory Frequency. The frequency used for self-announce position and intentions at non-towered airports. Often the same as UNICOM (122.8 MHz) or MULTICOM (122.9 MHz).

D

DA
Decision Altitude. The altitude on a precision approach (ILS or LPV) at which the pilot must decide to continue to land or execute a missed approach. Replaces the term Decision Height (DH) in modern usage.
DPE
Designated Pilot Examiner. An experienced pilot authorized by the FAA to conduct practical tests (checkrides) for pilot certificates and ratings. DPEs are not FAA employees but act under FAA authority.
DUATS
Direct User Access Terminal System. A legacy system that allowed pilots to file flight plans and receive weather briefings electronically. Now largely replaced by Leidos Flight Service and 1800wxbrief.com.

E

EFB
Electronic Flight Bag. A computing device used by pilots for flight operations including charts, approach plates, weather, weight and balance, and performance calculations. Must comply with AC 120-76D for Part 121/135 operations.
ELT
Emergency Locator Transmitter. A device that broadcasts a distress signal on 121.5 MHz and 406 MHz when activated by impact forces. Required on most GA aircraft per 14 CFR 91.207.
ETA
Estimated Time of Arrival. The projected time at which an aircraft will arrive at its destination, based on current groundspeed and remaining distance.
ETD
Estimated Time of Departure. The projected time at which an aircraft will depart from an airport.

F

FAF
Final Approach Fix. The point on an instrument approach where the final approach segment begins. On non-precision approaches, this is where descent to the MDA begins. Identified by a Maltese cross on approach plates.
FAR
Federal Aviation Regulation. Common informal term for Title 14 of the Code of Federal Regulations (14 CFR), which governs aviation in the United States.
FBO
Fixed-Base Operator. A commercial business at an airport that provides services such as fuel, hangar space, aircraft rental, maintenance, and pilot amenities.
FL
Flight Level. Altitude expressed in hundreds of feet when the altimeter is set to 29.92" Hg. FL180 = 18,000 feet pressure altitude. Used at and above 18,000 feet MSL (Class A airspace).
FRAT
Flight Risk Assessment Tool. A structured checklist used during preflight planning to evaluate cumulative risk factors including weather, pilot experience, aircraft condition, and external pressures. The FAA encourages FRAT use for all GA flights.
FSS
Flight Service Station. A facility providing pilot briefings, flight plan services, en-route advisories, search and rescue, and assistance to lost or emergency aircraft. Now operated by Leidos as a contracted service.

G

G-AIRMET
Graphical AIRMET. A graphical representation of AIRMET information presented on a map for easier interpretation. Available at aviationweather.gov. Shows areas of IFR conditions, turbulence, icing, and strong surface winds.
GA
General Aviation. All civil aviation except scheduled air service and military aviation. Encompasses private flying, flight training, aerial work, business aviation, and on-demand charter operations.
GFA
Graphical Forecasts for Aviation. A web-based product from the Aviation Weather Center that replaced the legacy Area Forecast (FA). Provides graphical depictions of forecast clouds, turbulence, icing, and surface conditions.
GPS
Global Positioning System. A satellite-based radio navigation system providing position, velocity, and time information. The foundation for RNAV approaches, ADS-B, and modern area navigation.
GS
Glideslope. The vertical guidance component of an ILS approach. Typically set at 3 degrees, providing the correct descent path to the runway threshold.

H

HIRL
High Intensity Runway Lights. The brightest category of runway edge lights, used at airports with precision instrument approaches.

I

IAF
Initial Approach Fix. The point where an instrument approach procedure begins. Multiple IAFs may exist for a single approach, each providing a different transition route.
IFR
Instrument Flight Rules. Rules governing flight when visibility is below VFR minimums or in controlled airspace above FL180. Requires an instrument rating, an IFR-equipped aircraft, and an ATC clearance.
ILS
Instrument Landing System. A precision approach system providing both lateral (localizer) and vertical (glideslope) guidance. The most common precision approach in the US. Minimums typically 200 feet DA and 1/2 mile visibility.
IMC
Instrument Meteorological Conditions. Weather conditions below the minimums prescribed for VFR flight. Requires instrument rating and IFR flight plan. VFR flight into IMC is a leading cause of fatal GA accidents.
IPC
Instrument Proficiency Check. A check with a CFII, examiner, or check airman required when an instrument-rated pilot has not met the recency-of-experience requirements of 14 CFR 61.57(c). Restores instrument currency.

K

KIAS
Knots Indicated Airspeed. The airspeed read directly from the airspeed indicator, uncorrected for installation and instrument errors. Used for compliance with operating limitations and V-speeds.
KTAS
Knots True Airspeed. Indicated airspeed corrected for air density (temperature and pressure altitude). Used for flight planning, navigation, and performance calculations.

L

LOC
Localizer. The lateral guidance component of an ILS. Also available as a standalone approach (LOC approach) providing only lateral guidance without a glideslope. Localizer width is typically 5 degrees (700 feet wide at the threshold).
LOC-I
Loss of Control — In-flight. The most common fatal accident category in general aviation. Includes aerodynamic stalls, spins, spiral dives, and any situation where the pilot loses the ability to control the aircraft in flight.
LPV
Localizer Performance with Vertical guidance. A GPS-based precision-like approach using WAAS. Provides both lateral and vertical guidance with minimums comparable to an ILS (as low as 200 feet DA). Does not require ground-based equipment.

M

MAP
Missed Approach Point. The point on a non-precision approach where the missed approach procedure must be initiated if the runway environment is not in sight. On precision approaches, the DA serves this function.
MDA
Minimum Descent Altitude. The lowest altitude on a non-precision approach to which descent is authorized without the runway in sight. The pilot must level off at MDA and may not descend further until identifying the runway environment.
MEA
Minimum En-route Altitude. The lowest altitude on a published airway that ensures obstacle clearance, adequate navigation signal reception, and ATC communication coverage.
METAR
Meteorological Aerodrome Report. A standardized format for reporting current surface weather conditions at an airport. Issued hourly by ASOS/AWOS stations. Special METARs (SPECI) are issued when conditions change significantly.
MOA
Military Operations Area. Airspace designated for military training activities. VFR traffic is permitted but should exercise extreme caution. IFR traffic is separated from military activity by ATC.
MSL
Mean Sea Level. Altitude measured from average sea level. Airport elevations, airway altitudes, and most charted altitudes are expressed in MSL. Used with the altimeter setting from the nearest reporting station.
MVFR
Marginal Visual Flight Rules. Weather conditions with ceiling 1,000-3,000 feet AGL and/or visibility 3-5 statute miles. Legal for VFR flight but requires caution. Depicted in blue on weather products.

N

NDB
Non-Directional Beacon. A ground-based radio transmitter that broadcasts on a specific frequency. Used with the ADF for navigation. Being phased out in the US as GPS-based navigation becomes standard.
NORDO
No Radio. An aircraft operating without radio communication capability. Permitted in most uncontrolled airspace and some controlled airspace with prior arrangements (light gun signals from tower).
NOTAM
Notice to Air Missions (formerly Notice to Airmen). A notice containing time-critical information essential to flight safety. Covers runway closures, airspace restrictions, navaid outages, and other hazards. Checking NOTAMs is required by 14 CFR 91.103.
NWS
National Weather Service. The US government agency responsible for aviation weather products including METARs, TAFs, AIRMETs, SIGMETs, and area forecasts. Products available at aviationweather.gov.

O

OAT
Outside Air Temperature. The ambient air temperature measured by an aircraft sensor. Used with pressure altitude to determine density altitude, which affects aircraft performance.

P

PA
Pressure Altitude. The altitude indicated when the altimeter is set to 29.92" Hg (standard pressure). Used for performance calculations and flight above 18,000 feet MSL.
PAPI
Precision Approach Path Indicator. A visual glide path aid consisting of four light units beside the runway. Two red/two white indicates on the correct 3-degree glidepath.
PIC
Pilot in Command. The pilot responsible for the operation and safety of an aircraft during flight. The PIC has final authority and responsibility for the flight per 14 CFR 91.3.
PIREP
Pilot Report. A report of actual flight conditions observed by a pilot, submitted to ATC or FSS. PIREPs are critical for reporting icing, turbulence, wind shear, and cloud conditions that automated systems cannot observe.
POH
Pilot's Operating Handbook. The FAA-approved document for a specific aircraft containing operating limitations, emergency procedures, normal procedures, performance data, weight and balance, and systems descriptions.
PPL
Private Pilot License/Certificate. Authorizes the holder to act as PIC for personal or recreational purposes. May carry passengers but may not fly for compensation or hire. Requires minimum 40 hours total time under Part 61.
PTS
Practical Test Standards. The legacy FAA document that defined standards for practical tests. Largely replaced by the Airman Certification Standards (ACS) for most certificates and ratings.

R

RA
Resolution Advisory. A command from TCAS II directing the pilot to climb or descend to avoid a traffic conflict. Pilots are required to follow RA commands immediately, even if it conflicts with an ATC instruction.
RNAV
Area Navigation. A navigation method that allows aircraft to fly on any desired flight path, rather than point-to-point along ground-based navaids. GPS is the primary RNAV sensor in modern aircraft.

S

SA
Situational Awareness. A pilot's mental model of the current state and projected future state of the flight. Includes position, weather, traffic, fuel state, systems status, and ATC communications.
SDP
Single Pilot Resource Management. The application of CRM principles to single-pilot operations. Focuses on workload management, automation management, task prioritization, and decision-making.
SIGMET
Significant Meteorological Information. An advisory for weather conditions hazardous to all aircraft. Covers severe icing, severe or extreme turbulence, volcanic ash, dust storms, and sandstorms reducing visibility below 3 miles.
SID
Standard Instrument Departure. A published IFR departure procedure providing obstacle clearance and an orderly transition from the terminal area to the en-route structure.
STAR
Standard Terminal Arrival Route. A published IFR arrival procedure providing an orderly transition from the en-route structure to the terminal area and approach.
SVFR
Special VFR. A clearance that allows VFR flight within Class B, C, D, or E surface areas when weather is below basic VFR minimums but the pilot can maintain clear of clouds and 1 SM visibility. Requires ATC clearance.

T

TA
Traffic Advisory. An alert from TCAS indicating nearby traffic that may pose a threat. Informational only — no maneuver is commanded. Displayed as a yellow circle on TCAS displays.
TCAS
Traffic Collision Avoidance System. An airborne system that interrogates nearby transponders to detect and display traffic, and provides Resolution Advisories to avoid collisions. Required on aircraft with more than 30 seats.
TAF
Terminal Aerodrome Forecast. A weather forecast for the area within 5 statute miles of an airport. Valid for 24 or 30 hours. Issued four times daily. Includes wind, visibility, weather, clouds, and change groups.
TFR
Temporary Flight Restriction. A regulatory action that restricts certain aircraft from operating in a defined area on a temporary basis. Common for VIP movements, sporting events, disaster areas, and military operations. Always check before flight.
TRSA
Terminal Radar Service Area. Airspace where radar service is available to VFR aircraft but participation is voluntary. Located at airports that do not qualify for Class C but have radar approach control.

V

VFR
Visual Flight Rules. Rules governing flight when weather conditions meet or exceed specified minimums (generally 3 SM visibility and 1,000-foot ceiling). The pilot maintains visual reference to the ground and is responsible for see-and-avoid traffic separation.
VMC
Visual Meteorological Conditions. Weather conditions that meet or exceed the minimums for VFR flight. Specific minimums vary by airspace class and altitude.
VOR
VHF Omnidirectional Range. A ground-based radio navigation aid providing 360 degrees of azimuth information. The backbone of the federal airway system, though being gradually decommissioned as GPS navigation expands.
VSI
Vertical Speed Indicator. A flight instrument that displays the rate of climb or descent in feet per minute. Also called a variometer. Standard rate of descent on an ILS glideslope is approximately 500-700 fpm depending on groundspeed.

W

W&B
Weight and Balance. The process of calculating aircraft total weight and center of gravity position to ensure both are within approved limits. Required by 14 CFR 91.9 and 91.103 before every flight.
WAAS
Wide Area Augmentation System. A GPS enhancement system that improves accuracy, integrity, and availability of GPS signals. Enables LPV approaches with minimums comparable to ILS. Requires a WAAS-capable GPS receiver.
WINGS
The FAA's Pilot Proficiency Program. A voluntary program that provides structured recurrent training through online courses and flight activities. Completing a WINGS phase satisfies the Flight Review requirement of 14 CFR 61.56.

Related guides

How to Read METARs and TAFsDecode aviation weather reports and forecasts with real examples.US Airspace ClassesClass A through G — requirements, dimensions, and weather minimums.Part 61 Pilot CertificatesCertificate tiers, requirements, privileges, and endorsements.