Learning Library
Glossary
Aviation terminology explained clearly — from METAR to NOTAM and beyond.
134 terms
Type to filter terms. The full A-Z glossary is listed below.
A
ADS-B
Automatic Dependent Surveillance–Broadcast — a satellite-based system where aircraft broadcast their GPS position, altitude, and speed, enhancing surveillance coverage and accuracy.
adverse yaw
An unwanted yaw in the direction opposite to a turn, caused by unequal drag on the ailerons — corrected with rudder input.
AGL
Above Ground Level — altitude measured from the terrain directly below the aircraft, as opposed to above mean sea level (MSL).
aileron
A hinged control surface on the trailing edge of each wing that controls roll by moving asymmetrically — one goes up while the other goes down.
aircraft category
A classification system based on approach speed or maximum takeoff weight — determines minimum separation, approach procedures, and runway requirements.
aircraft icing
The accumulation of ice on an aircraft's external surfaces during flight through visible moisture at freezing temperatures — degrades aerodynamic performance and adds weight.
AIRMET
Airmen's Meteorological Information — a weather advisory for conditions hazardous primarily to light aircraft, including moderate turbulence, icing, and low visibility.
altimeter setting
The barometric pressure value set on an aircraft's altimeter so that it reads field elevation on the ground — provided in METARs and by ATC.
ancillary revenue
Revenue from non-ticket sources such as baggage fees, seat selection, onboard sales, and loyalty programs — an increasingly important component of airline profitability.
angle of attack
The angle between a wing's chord line and the relative wind — the primary factor determining lift and stall behavior.
AOA indicator
Angle of Attack indicator — a cockpit instrument that displays the aircraft's current angle of attack, providing direct stall margin information.
apron
The paved area at an airport where aircraft are parked, loaded, fueled, and boarded — also called the ramp or tarmac.
ATC
Air Traffic Control — the ground-based service that directs aircraft on the ground and in controlled airspace to maintain safe separation.
ATIS — Automatic Terminal Information Service
ATIS (Automatic Terminal Information Service) is a continuous broadcast of recorded aeronautical information at busier airports, providing arriving and departing pilots with essential weather and operational data.
B
baggage handling system
The integrated conveyor, sorting, and tracking infrastructure at an airport that moves checked luggage between check-in, security screening, aircraft, and claim areas.
baggage reconciliation
The security process ensuring every checked bag loaded on an aircraft is matched to a boarded passenger — a critical security requirement.
bank angle
The angle of the aircraft's wings relative to the horizon during a turn — directly determines load factor, turn rate, and effective stall speed.
BECMG
Becoming — a TAF change indicator meaning conditions are expected to gradually transition to a new state within a specified time window.
BKN
Broken — a cloud cover designation in METARs meaning 5/8 to 7/8 of the sky is covered, constituting a ceiling.
bleed air
Compressed air extracted from a jet engine's compressor section — used for cabin pressurization, anti-icing, and pneumatic systems.
block hour
The time from when an aircraft pushes back from the gate (blocks out) to when it arrives at the gate at the destination (blocks in) — the standard unit for measuring aircraft utilization.
bypass ratio
The ratio of air passing around (bypass) a turbofan's core to air passing through the core — higher ratios mean greater fuel efficiency and lower noise.
C
cabin pressurization
The process of maintaining air pressure inside an aircraft cabin at a livable level while cruising at high altitudes where ambient pressure is dangerously low.
CASM
Cost per Available Seat Mile — a key airline efficiency metric measuring the operating cost of flying one seat one mile, regardless of whether it is occupied.
CAVOK
Ceiling and Visibility OK — a METAR/TAF abbreviation indicating visibility 10 km or more, no cloud below 5,000 ft or below the highest minimum sector altitude, and no significant weather.
ceiling
The height of the lowest layer of clouds reported as broken (BKN) or overcast (OVC) — determines VFR/IFR conditions and approach minimums.
center of gravity
The point at which an aircraft's total weight acts as if concentrated — its position relative to the wing determines stability and control authority.
chord line
The straight line connecting the leading edge to the trailing edge of an airfoil — used as the reference for measuring angle of attack.
clear air turbulence
Turbulence encountered in cloud-free air, typically near jet streams and at high altitudes — invisible to radar and difficult to forecast precisely.
codeshare
An arrangement where two or more airlines share the same flight, each marketing it under their own designator code — expanding network reach without operating additional aircraft.
cold front
A boundary where a cold air mass advances and undercuts a warmer air mass — producing narrow bands of intense weather including thunderstorms, turbulence, and wind shifts.
controlled airspace
Airspace classes (A, B, C, D, E) where ATC provides separation services and communication is required — entry restrictions vary by class.
critical angle
The angle of attack at which a wing produces maximum lift — exceeding it causes airflow separation and an aerodynamic stall.
crosswind
A wind blowing perpendicular to the runway or aircraft track — requiring pilot compensation during takeoff, approach, and landing to maintain alignment.
cumulonimbus
A towering, anvil-shaped cloud associated with thunderstorms — producing severe turbulence, lightning, hail, heavy precipitation, and wind shear.
D
decision height
The specified altitude on a precision approach at which a pilot must decide whether to land or execute a missed approach — based on whether the runway environment is visible.
deicing
The application of heated glycol-based fluid to an aircraft on the ground to remove snow, ice, or frost before takeoff — ensuring clean wing surfaces for safe flight.
density altitude
Pressure altitude corrected for non-standard temperature — the altitude at which the air density matches standard atmosphere conditions, affecting aircraft performance.
differential pressure
The difference between cabin pressure and outside atmospheric pressure — the primary structural load on a pressurized fuselage during flight.
dispatch reliability
The percentage of scheduled flights that depart without a mechanical cancellation or delay exceeding a defined threshold — a key indicator of airline operational quality.
diversion
The rerouting of a flight to an airport other than its planned destination — triggered by weather, mechanical issues, fuel shortage, or medical emergencies.
downdraft
A column of sinking air within or near a convective cell — can produce rapid altitude loss and is particularly hazardous near the ground.
drag
The aerodynamic force opposing an aircraft's motion through the air — composed of parasite drag and induced drag.
drag coefficient
A dimensionless number (CD) quantifying the total aerodynamic drag on a body, used in the drag equation.
E
EASA
European Union Aviation Safety Agency — the EU authority responsible for civil aviation safety regulation, aircraft certification, and operational standards across Europe.
elevator
A hinged control surface on the horizontal stabilizer that controls pitch — deflecting it changes the aircraft's nose-up or nose-down attitude.
empennage
The tail assembly of an aircraft, including the horizontal stabilizer, elevator, vertical stabilizer, and rudder — provides pitch and yaw stability.
ETOPS
Extended-range Twin-engine Operations — certification allowing twin-engine aircraft to fly routes far from diversion airports, based on demonstrated engine and systems reliability.
F
FAA
Federal Aviation Administration — the U.S. government agency responsible for regulating civil aviation, certifying aircraft, and managing the national airspace system.
flap
A high-lift device on the trailing edge of the wing that increases both lift and drag when extended — used to reduce takeoff and landing speeds.
flight data recorder
A crash-survivable device that records flight parameters (altitude, speed, heading, control inputs, engine data) — essential for accident investigation.
flight level
An altitude expressed in hundreds of feet when the altimeter is set to 29.92 inHg — used for vertical separation above the transition altitude.
flight plan
A document filed with ATC containing the planned route, altitude, speed, fuel, and other details for a flight — required for IFR operations and recommended for VFR.
fuel burn
The rate at which an aircraft consumes fuel, typically expressed in pounds or kilograms per hour — a critical factor in range, cost, and environmental impact.
fuselage
The main body of an aircraft that houses the crew, passengers, and cargo — its shape significantly affects aerodynamic drag and structural integrity.
G
gate
A designated position at an airport terminal where aircraft park for passenger boarding and deplaning, connected by a jet bridge or accessed by stairs.
GDS
Global Distribution System — a network that enables travel agencies and websites to search, book, and issue tickets for airline seats, hotel rooms, and car rentals.
go-around
The maneuver of aborting a landing attempt and climbing away to reposition for another approach — a standard procedure, not an emergency.
ground speed
The actual speed of an aircraft relative to the ground — true airspeed adjusted for wind, determining time en route and fuel burn.
H
holding pattern
A racetrack-shaped flight path where aircraft circle in a defined area while awaiting clearance to proceed — used when arrival traffic exceeds airport capacity.
hub-and-spoke
An airline network model where flights radiate from central hub airports, connecting passengers through hub transfers — maximizing network connectivity from fewer routes.
I
IATA
International Air Transport Association — the global trade association for airlines, responsible for 3-letter airport and airline codes, ticketing standards, and industry coordination.
ICAO
International Civil Aviation Organization — the UN specialized agency that sets global standards for aviation safety, security, and efficiency.
IFR — Instrument Flight Rules
Instrument Flight Rules (IFR) govern flight operations conducted primarily by reference to instruments rather than visual references, enabling safe navigation in low-visibility and cloud conditions.
ILS
Instrument Landing System — a precision radio-based approach system providing lateral (localizer) and vertical (glideslope) guidance for landing in low visibility.
indicated airspeed
The airspeed reading displayed directly on the cockpit instrument, based on dynamic pressure — uncorrected for installation error, compressibility, or density altitude.
induced drag
Drag that is a direct byproduct of lift generation, caused by wingtip vortices deflecting the local airflow — increases at lower speeds and higher angles of attack.
interline
An agreement between airlines allowing passengers to use a single ticket across multiple carriers, with coordinated baggage transfer and ticketing.
J
K
L
lift
The aerodynamic force perpendicular to the relative wind that supports an aircraft in flight — generated primarily by the wings.
lift coefficient
A dimensionless number (CL) that quantifies the lift generated by an airfoil at a given angle of attack, used in the lift equation.
load factor
The ratio of total lift to aircraft weight, expressed in G units — increases during turns, turbulence, and pull-ups, raising effective stall speed.
load factor (airline metric)
The percentage of available seats that are filled with paying passengers — a key measure of airline capacity utilization.
M
Mach number
The ratio of an aircraft's true airspeed to the local speed of sound — used for high-altitude cruise speed reference and buffet boundary management.
mean aerodynamic chord
The reference chord length of a wing used for aerodynamic calculations, CG positioning, and stability analysis.
METAR — Meteorological Aerodrome Report
METAR is a standardized format for reporting current weather observations at airports. Issued hourly, it provides pilots and controllers with temperature, wind, visibility, cloud, and pressure data.
microburst
A localized, intense downdraft that spreads outward on contact with the ground, producing sudden wind speed changes of 30–100+ knots — extremely hazardous during takeoff and approach.
minimum equipment list
An approved document listing aircraft equipment that may be inoperative for dispatch under specific conditions — enables flight without grounding for minor unserviceabilities.
missed approach
A prescribed procedure executed when a pilot cannot establish sufficient visual reference at the decision height — involving a climb, turn, and repositioning for another attempt.
mountain wave
An atmospheric wave pattern formed when stable air flows over mountainous terrain — can produce severe turbulence, rotors, and extreme altitude deviations.
MSL
Mean Sea Level — the standard reference datum for altitude measurement, used on aeronautical charts and for altimeter calibration.
MTOW
Maximum Takeoff Weight — the highest weight at which an aircraft is certified to begin its takeoff roll, limited by structural, performance, and regulatory constraints.
N
nautical mile
A unit of distance equal to one minute of latitude (1,852 meters / 6,076 feet) — the standard unit for aviation and maritime distances.
NOTAM — Notice to Air Missions
A NOTAM (Notice to Air Missions) is an official notice containing information essential to personnel concerned with flight operations, alerting them to hazards, changes, or temporary conditions.
NTSB
National Transportation Safety Board — the independent U.S. agency that investigates civil aviation accidents and issues safety recommendations.
O
occluded front
A complex frontal boundary where a cold front overtakes a warm front, combining weather characteristics of both — often producing widespread precipitation and turbulence.
on-time performance
The percentage of flights arriving within 15 minutes of their scheduled arrival time — a widely tracked airline and airport operational metric.
OVC
Overcast — a cloud cover designation in METARs meaning 8/8 of the sky is completely covered by cloud, always constituting a ceiling.
P
parasite drag
All aerodynamic drag not related to lift production — includes form drag, skin friction drag, and interference drag — increases with the square of airspeed.
PIREP
Pilot Report — a report of actual weather conditions encountered in flight, submitted by pilots and used to supplement forecast data.
pitch
Rotation about the aircraft's lateral axis — controlled by the elevator, determining the nose-up or nose-down attitude.
POH
Pilot's Operating Handbook — the FAA-approved document containing operating limitations, performance charts, and procedures specific to an aircraft type and serial number.
point-to-point
An airline network model where flights connect cities directly without routing through a central hub — common among low-cost carriers, offering faster travel times.
pressure altitude
The altitude indicated when the altimeter is set to the standard datum of 29.92 inHg (1013.25 hPa) — used for aircraft separation above transition altitude.
pushback
The procedure of moving an aircraft backward from the gate using a tug or tractor, since aircraft cannot easily reverse under their own power.
R
RASM
Revenue per Available Seat Mile — an airline metric measuring total revenue generated per seat mile flown, combining ticket and ancillary revenue.
revenue management
The practice of dynamically adjusting fares and inventory to maximize total revenue — using demand forecasting, booking curves, and fare class controls.
roll
Rotation about the aircraft's longitudinal axis — controlled by ailerons, producing bank angle for turning.
rudder
A hinged control surface on the vertical stabilizer that controls yaw — used for coordinated turns, crosswind corrections, and asymmetric thrust management.
runway
A defined rectangular area on an airport prepared for aircraft takeoff and landing — designated by a number based on its magnetic heading.
RVR
Runway Visual Range — an instrumentally measured distance over which a pilot can see runway markings or lights from the approach end, reported in feet or meters.
S
SIGMET
Significant Meteorological Information — an advisory issued for hazardous weather phenomena (thunderstorms, severe turbulence, volcanic ash, icing) that pose a risk to all aircraft.
slat
A high-lift device on the leading edge of the wing that extends to increase the critical angle of attack — delays the stall to lower speeds.
slot
A designated time window at a capacity-constrained airport during which an airline is authorized to operate a takeoff or landing — a scarce and valuable resource.
SMS
Safety Management System — a systematic approach to managing safety, including organizational structure, accountability, policies, and procedures, as required by ICAO for airlines and airports.
SPECI
Special METAR — an unscheduled weather observation issued when conditions change significantly between routine hourly reports.
spoiler
A flat plate on the upper wing surface that deploys upward to disrupt airflow, reducing lift and increasing drag — used for speed control, roll assist, and ground deceleration.
squawk
A four-digit transponder code assigned by ATC for radar identification — special codes (7500, 7600, 7700) indicate hijack, communication failure, or emergency.
stall speed
The minimum airspeed at which a wing can maintain level flight at a given weight, configuration, and load factor — below this speed, a stall occurs.
T
TAF
Terminal Aerodrome Forecast — a coded weather forecast for the area within 5 statute miles of an airport, covering a 24- or 30-hour period.
taxiway
A defined path at an airport connecting runways to aprons, gates, and other facilities — designated by letters and used for aircraft ground movement.
TCAS
Traffic Collision Avoidance System — an airborne system that independently detects nearby transponder-equipped aircraft and provides resolution advisories to prevent mid-air collisions.
TEMPO
Temporary — a TAF change indicator meaning conditions are expected to fluctuate temporarily, lasting less than an hour each time.
thermal
A column of rising warm air generated by uneven surface heating — used by glider pilots for lift and a source of convective turbulence for powered aircraft.
thrust
The forward force produced by an aircraft's engines — must overcome drag for acceleration and equal drag for constant speed flight.
transponder
An electronic device that receives radar interrogations and transmits a coded response with identification and altitude data — essential for ATC radar surveillance.
trim tab
A small adjustable surface on a primary control surface that provides a constant aerodynamic force, relieving the pilot of sustained control pressure.
tropopause
The boundary between the troposphere and stratosphere, where temperature stops decreasing with altitude — important for turbulence prediction and flight level selection.
true airspeed
The actual speed of the aircraft through the air mass, corrected for altitude and temperature — used for flight planning and navigation.
TSA
Transportation Security Administration — the U.S. agency responsible for security screening of passengers and baggage at airports.
turbofan
A jet engine with a large fan at the front that bypasses much of the airflow around the core — the dominant powerplant on modern commercial aircraft, offering high efficiency and low noise.
turboprop
A gas turbine engine that drives a propeller through a reduction gearbox — efficient at lower speeds and altitudes, commonly used on regional aircraft.
turnaround time
The elapsed time between an aircraft's arrival at the gate and its departure on the next flight — a critical factor in aircraft utilization and schedule reliability.
U
V
V-speeds
Standardized airspeed references (V1, Vr, V2, Vref, Vne, etc.) that define critical operational limits and targets for each phase of flight.
VFR — Visual Flight Rules
Visual Flight Rules (VFR) are a set of regulations that allow pilots to fly by visual reference to the ground and other aircraft, requiring minimum weather conditions for visibility and cloud clearance.
visibility
The greatest horizontal distance at which prominent objects can be seen and identified — a primary factor in determining flight rule applicability and approach minimums.
W
wake turbulence
Turbulence generated by wingtip vortices trailing behind an aircraft — particularly dangerous for smaller aircraft following larger ones during approach and departure.
warm front
A boundary where a warm air mass advances over a retreating cold air mass — producing widespread low ceilings, poor visibility, and steady precipitation ahead of the front.
waypoint
A predetermined geographical position defined by coordinates or a named fix, used for navigation and to define airways, approaches, and departure procedures.
weight
The gravitational force acting on the aircraft — one of the four forces of flight, opposed by lift and affected by fuel burn, payload, and loading.
wind shear
A sudden change in wind speed or direction over a short distance — hazardous during takeoff and approach, capable of causing rapid airspeed and altitude changes.