Aviation Glossary

A

ADF (Automatic Direction Finder)

A radio navigation instrument that determines the bearing to an NDB (Non-Directional Beacon) ground station relative to the aircraft's heading.

ADS-B (Automatic Dependent Surveillance-Broadcast)

A surveillance technology where aircraft broadcast their GPS-derived position, altitude, and velocity, enabling air traffic control and other aircraft to track them in real time.

Aerodrome

A defined area on land or water used for the arrival, departure, and surface movement of aircraft. Includes both airports and smaller airfields.

AGL (Above Ground Level)

A measurement of altitude expressed as the height above the terrain directly below the aircraft.

Ailerons

Hinged control surfaces on the trailing edge of each wing that control roll (bank) by moving in opposite directions.

AIM (Aeronautical Information Manual)

The FAA's official guide to basic flight information and ATC procedures for pilots operating in the US National Airspace System.

Airframe

The mechanical structure of an aircraft, excluding engines, avionics, and other systems. Includes the fuselage, wings, and empennage.

Airmet (Airmen's Meteorological Information)

A weather advisory issued for conditions that may affect light aircraft, including moderate turbulence, icing, and low visibility.

Airspeed

The speed of an aircraft relative to the surrounding air mass. Distinguished from ground speed, which is speed relative to the ground. See: Navigation

Airway

A designated corridor of controlled airspace between navigation aids, defined by a centreline and width, used for en-route IFR flight.

Altimeter

An instrument that measures altitude by sensing atmospheric pressure and converting it to a height reading based on the altimeter setting (QNH/QFE).

AMSL (Above Mean Sea Level)

A standard datum for expressing altitude, measured vertically from mean sea level. Most aerodrome elevations and airspace boundaries are given in AMSL.

AOA (Angle of Attack)

The angle between the chord line of the wing and the relative wind. Exceeding the critical angle of attack causes an aerodynamic stall regardless of airspeed.

AOPA (Aircraft Owners and Pilots Association)

The world's largest civil aviation membership organisation, representing the interests of general aviation pilots and aircraft owners.

Approach

The phase of flight in which an aircraft descends toward an aerodrome for the purpose of landing, often following a published instrument approach procedure. See: Approach & Landing

APU (Auxiliary Power Unit)

A small gas-turbine engine, typically in the tail section, that provides electrical power and pneumatic air for engine starting and cabin systems while on the ground.

ATC (Air Traffic Control)

The ground-based service responsible for directing aircraft on the ground and in controlled airspace, ensuring safe separation between aircraft. See: ATC Phraseology

ATIS (Automatic Terminal Information Service)

A continuous broadcast of recorded aerodrome information including weather, runway in use, and relevant NOTAMs, identified by a phonetic letter.

Autopilot

An automated system that controls the aircraft's flight path without constant manual input, capable of maintaining heading, altitude, speed, and executing programmed routes.

Avionics

Electronic systems used in aircraft, including communication radios, navigation equipment, flight management systems, and display units.

Azimuth

The horizontal angular direction of a bearing, measured clockwise from north. Used in radar displays and navigation to express the direction to a target or waypoint.

B

Backtrack

To taxi along a runway in the opposite direction to the landing or take-off direction, typically to reach the start of the runway at airports without taxiway access.

Barometric Pressure

The pressure exerted by the atmosphere at a given point, measured in hectopascals (hPa) or inches of mercury (inHg), used to set altimeters.

Base Leg

The flight path at right angles to the extended centreline of the landing runway, flown between downwind and final approach in a standard traffic pattern.

Bearing

The horizontal direction of one point from another, expressed in degrees from north (either magnetic or true). See: Navigation

Block Time

The total elapsed time from when an aircraft first moves under its own power (blocks off) to when it comes to rest at the destination gate (blocks on).

Braking Action

A report on the effectiveness of runway braking, rated as good, medium, poor, or nil, often due to contamination such as snow, ice, or standing water.

Briefing

A structured presentation of flight-relevant information before departure, covering weather, NOTAMs, route, fuel, and expected procedures.

Buster

A term used primarily in military aviation meaning to fly at maximum continuous speed.

BARO-VNAV

A vertical navigation method using barometric altitude data to provide vertical guidance on RNAV approaches, less precise than SBAS but widely available.

C

Calibrated Airspeed (CAS)

Indicated airspeed corrected for instrument and position errors. CAS equals true airspeed only in standard sea-level conditions.

CAVOK (Ceiling and Visibility OK)

A METAR abbreviation meaning visibility is 10 km or more, no cloud below 5,000 ft or the highest minimum sector altitude, and no significant weather. See: METAR & Weather

Ceiling

The height above ground of the lowest layer of cloud reported as broken (BKN) or overcast (OVC), or the vertical visibility in obscuring phenomena.

Circling Approach

A visual manoeuvre after completing an instrument approach, used when the runway in use is not aligned with the approach procedure. See: Approach & Landing

Class A Airspace

Controlled airspace from FL180 to FL600 (US) where only IFR flight is permitted and all aircraft must have an ATC clearance. See: Airspace Classification

Class B Airspace

Controlled airspace surrounding the busiest airports, requiring ATC clearance, two-way radio, and a Mode C transponder for all aircraft. See: Airspace Classification

Class C Airspace

Controlled airspace surrounding airports with an operational control tower and radar approach control, requiring two-way radio and transponder. See: Airspace Classification

Class D Airspace

Controlled airspace around airports with an operating control tower, requiring two-way radio communication prior to entry. See: Airspace Classification

Class E Airspace

Controlled airspace that is not Class A, B, C, or D. IFR flights require ATC clearance; VFR flights do not but must comply with visibility and cloud separation rules. See: Airspace Classification

Class G Airspace

Uncontrolled airspace where ATC has no authority or obligation to provide separation. Pilots are responsible for their own traffic avoidance. See: Airspace Classification

Clearance

An authorisation issued by ATC for an aircraft to proceed under specified conditions within controlled airspace. A clearance is not an instruction to violate regulations.

Climb

The phase of flight in which an aircraft gains altitude, achieved by increasing the angle of attack and/or adding power to produce a positive rate of climb.

Cockpit

The section at the front of the aircraft where the flight crew operate the controls and instruments. Also called the flight deck on larger aircraft.

Comms (Communications)

Radio communication equipment and frequencies used for pilot-ATC interaction, including VHF, HF, and SATCOM systems. See: Radio Telephony

Controlled Airspace

Airspace of defined dimensions within which ATC services are provided. Includes Class A, B, C, D, and E airspace. See: Airspace Classification

Course

The intended direction of flight, measured as the angle between north and the flight path over the ground. Distinguished from heading, which accounts for wind correction.

Crosswind

A wind component blowing perpendicular to the direction of travel or the runway centreline. Pilots apply crosswind correction techniques during take-off and landing.

CTA (Control Area)

A controlled airspace extending upward from a specified height above the surface, typically surrounding an airport or airway.

CTR (Control Zone)

A controlled airspace extending from the surface upward to a specified limit, usually around an airport, protecting arriving and departing IFR traffic.

D

DA (Decision Altitude)

The altitude in a precision approach at which the pilot must decide to either continue the approach (if visual references are acquired) or execute a missed approach. Expressed as altitude AMSL. See: Approach & Landing

Dead Reckoning

A navigation method that estimates current position by advancing a known position using course, speed, time, and wind data without reference to external navigation aids. See: Navigation

Density Altitude

Pressure altitude corrected for non-standard temperature. A critical performance metric, as high density altitude reduces engine power and aerodynamic lift.

Departure

The phase of flight immediately after take-off, including the initial climb and any published standard instrument departure (SID) procedure.

DH (Decision Height)

The height above the runway threshold at which a decision to land or go around must be made during a precision approach. Expressed relative to the threshold elevation. See: Approach & Landing

Displaced Threshold

A runway threshold that is not at the beginning of the paved surface. The preceding area may be used for taxiing and take-off but not for landing.

DME (Distance Measuring Equipment)

An avionics system that measures the slant-range distance between the aircraft and a ground transponder, displayed in nautical miles. See: Navigation

Downwind

The leg of a traffic pattern flown parallel to and in the opposite direction of the active runway. Aircraft on downwind prepare for the base turn and approach.

Drag

The aerodynamic force that opposes an aircraft's forward motion through the air. Comprises parasite drag (form, skin friction, interference) and induced drag (a by-product of lift).

DVOR (Doppler VOR)

A type of VOR ground station that uses the Doppler effect to generate a more accurate bearing signal, less susceptible to site errors caused by reflections from buildings and terrain.

E

EAT (Expected Approach Time)

The time at which ATC expects an arriving aircraft, subject to delay, will be cleared to commence its approach for landing.

EFIS (Electronic Flight Instrument System)

A flight deck display system that replaces traditional mechanical instruments with electronic screens showing attitude, navigation, and engine data.

EGPWS (Enhanced Ground Proximity Warning System)

An advanced terrain awareness system that uses GPS and a terrain database to provide predictive warnings of potential controlled flight into terrain.

Elevation

The vertical distance of a fixed point (such as an aerodrome) above mean sea level. Not to be confused with altitude, which refers to an airborne aircraft.

ELT (Emergency Locator Transmitter)

A radio transmitter that activates automatically on impact or manually by the crew, broadcasting a distress signal on 121.5 MHz and 406 MHz to aid search and rescue.

Emergency

A condition of distress or urgency. Distress (MAYDAY) is declared when an aircraft is threatened by grave and imminent danger; urgency (PAN PAN) when safety is a concern but not immediately life-threatening. See: Emergency Procedures

Empennage

The tail assembly of an aircraft, consisting of the horizontal stabiliser, elevator, vertical stabiliser (fin), and rudder.

ETA (Estimated Time of Arrival)

The predicted time at which an aircraft will arrive at a designated point, such as a waypoint, airport, or parking stand.

ETD (Estimated Time of Departure)

The predicted time at which an aircraft will depart from the gate or begin its take-off roll.

ETE (Estimated Time En Route)

The estimated total flying time from departure to destination, calculated using distance, planned speed, and forecast wind. See: Flight Planning

F

FAF (Final Approach Fix)

A designated point on a non-precision instrument approach where the final descent to the runway begins. In precision approaches this is typically the glideslope intercept point. See: Approach & Landing

FIR (Flight Information Region)

An airspace of defined dimensions within which flight information services and alerting services are provided. Every portion of the atmosphere belongs to a FIR.

Flaps

Hinged surfaces on the trailing edge of the wings that increase lift and drag when extended, allowing slower approach speeds and steeper descent angles.

Flare

The gentle pitch-up manoeuvre performed just before touchdown to reduce the descent rate and allow the aircraft to settle onto the runway smoothly.

Flight Level (FL)

A standard pressure altitude expressed in hundreds of feet with the altimeter set to 1013.25 hPa (29.92 inHg). For example, FL350 is 35,000 ft on the standard setting.

Flight Plan

A document filed with ATC or flight information services detailing the intended route, altitude, speed, fuel, and other details of a proposed flight. See: Flight Planning

FMS (Flight Management System)

A computer system that automates navigation, performance calculations, and flight plan management, integrating GPS, INS, and radio navigation inputs.

FOD (Foreign Object Debris / Damage)

Any object on an aerodrome movement area that could damage an aircraft. FOD damage is a significant safety and maintenance concern, especially to jet engines.

Fuel

Aviation fuel, principally Avgas (100LL) for piston engines and Jet A-1 (kerosene) for turbine engines. Flight planning must account for trip fuel, reserves, contingency, and alternate fuel. See: Flight Planning

G

GA (General Aviation)

All civil aviation operations other than scheduled air services and non-scheduled air transport operations for hire. Includes private, training, recreational, and business flights.

Glide Ratio

The ratio of horizontal distance travelled to altitude lost in a power-off glide. A higher glide ratio means the aircraft can travel further for each unit of altitude lost.

Glidepath

The planned descent profile towards the runway, defined by a specific angle (typically around 3 degrees) for a stabilised approach.

Glideslope (GS)

The vertical guidance component of an ILS that provides a precise descent angle (usually 3 degrees) to the runway touchdown zone. See: Approach & Landing

GNSS (Global Navigation Satellite System)

The generic term for satellite-based navigation systems, including GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China). See: Navigation

Go-Around

A manoeuvre in which a pilot aborts an approach and climbs away from the runway, either on instruction from ATC or by pilot decision due to unstable approach or traffic. See: Approach & Landing

GPS (Global Positioning System)

A satellite-based navigation system operated by the US that provides position, velocity, and timing information to receivers worldwide. See: Navigation

Ground Effect

A phenomenon where an aircraft experiences increased lift and reduced drag when flying very close to the surface (within approximately one wingspan), due to disruption of wingtip vortices.

Ground Speed (GS)

The speed of an aircraft relative to the ground, determined by true airspeed adjusted for wind. Ground speed determines actual progress along a route.

H

Heading

The direction in which the aircraft's nose is pointing, expressed in degrees from north. Heading differs from track when there is a crosswind component. See: Navigation

Holding Pattern

A racetrack-shaped manoeuvre flown at a specified fix, altitude, and heading to keep aircraft within a defined airspace while awaiting further ATC clearance.

HSI (Horizontal Situation Indicator)

A cockpit instrument that combines a heading indicator with a VOR/ILS course deviation indicator, providing an integrated view of the aircraft's lateral navigation situation.

Hypoxia

A condition caused by insufficient oxygen reaching body tissues, impairing judgement and motor function. Onset varies with altitude; supplemental oxygen is typically required above 10,000 ft.

Hydroplaning

A condition where a layer of water between the tyres and runway surface prevents effective braking and directional control. Risk increases with speed and water depth.

I

IAS (Indicated Airspeed)

The airspeed reading shown directly on the airspeed indicator, uncorrected for instrument, position, compressibility, or density errors.

ICAO (International Civil Aviation Organization)

A specialised agency of the United Nations that sets international standards and recommended practices (SARPs) for civil aviation safety, security, and efficiency.

Icing

The accumulation of ice on aircraft surfaces, occurring when the aircraft flies through visible moisture at temperatures at or below 0 degrees C. Disrupts airflow and adds weight.

IFR (Instrument Flight Rules)

A set of regulations permitting flight in instrument meteorological conditions (IMC) by reference to instruments and under ATC control, without requiring external visual references.

ILS (Instrument Landing System)

A precision approach aid providing both lateral guidance (localiser) and vertical guidance (glideslope) to the runway, enabling approaches in low visibility. See: Approach & Landing

IMC (Instrument Meteorological Conditions)

Weather conditions below the minimums specified for visual flight rules (VFR), requiring flight under IFR. Generally visibility below 5 km or cloud below certain limits.

Indicated Airspeed

See IAS. The uncorrected reading on the airspeed indicator, driven by the difference between pitot (total) pressure and static pressure.

INS (Inertial Navigation System)

A self-contained navigation system that computes position, velocity, and attitude using accelerometers and gyroscopes, without external radio signals.

J

Jet Blast

The high-velocity exhaust gases produced by jet engines, capable of causing damage to nearby aircraft, vehicles, and structures, and posing a serious hazard to personnel.

Jet Stream

A narrow band of strong winds (typically 60-200+ knots) found at high altitude, usually between 25,000 and 45,000 ft. Can significantly affect flight times and fuel burn. See: Meteorology

K

Kilogram (kg)

The SI unit of mass. In aviation, fuel, payload, and aircraft weight are commonly measured in kilograms outside the United States, where pounds (lbs) are used.

Knot (kt)

A unit of speed equal to one nautical mile per hour (approximately 1.852 km/h or 1.151 mph). The standard unit for airspeed, wind speed, and ground speed in aviation.

KTAS (Knots True Airspeed)

True airspeed expressed in knots, representing the actual speed of the aircraft through the air mass, corrected for altitude and temperature effects.

L

Landing

The final phase of flight in which the aircraft touches down on the runway, decelerates, and exits to a taxiway. See: Approach & Landing

Latitude

The angular distance north or south of the equator, expressed in degrees. Together with longitude, it defines a precise position on Earth. See: Navigation

Lift

The aerodynamic force generated by the wings perpendicular to the relative wind, opposing the weight of the aircraft and enabling flight.

LNAV (Lateral Navigation)

An RNAV approach mode providing lateral (left-right) guidance based on GPS or other RNAV sensors, without vertical guidance. See: Approach & Landing

Load Factor

The ratio of lift to aircraft weight, expressed in G units. In level flight the load factor is 1G; it increases in turns and manoeuvres.

Localiser (LOC)

The lateral guidance component of an ILS, transmitting a radio signal that defines the extended centreline of the runway. See: Approach & Landing

Longitude

The angular distance east or west of the prime meridian (Greenwich), expressed in degrees. Paired with latitude to define a position on Earth. See: Navigation

M

Mach Number

The ratio of the aircraft's true airspeed to the local speed of sound. Mach 1.0 equals the speed of sound; jet transports typically cruise around Mach 0.78-0.85.

Magnetic Bearing

A bearing measured with reference to magnetic north rather than true north, accounting for the local magnetic variation.

Magnetic Variation

The angular difference between true north and magnetic north at a given location. Also called magnetic declination. See: Navigation

MAP (Missed Approach Point)

The point in an instrument approach at which the missed approach procedure must be initiated if the required visual references are not established. See: Approach & Landing

MAYDAY

The international radiotelephony distress signal, spoken three times, indicating that the aircraft is in grave and imminent danger and requires immediate assistance. See: Emergency Procedures

MDA (Minimum Descent Altitude)

The lowest altitude to which descent is permitted on a non-precision approach without the required visual reference for landing. See: Approach & Landing

METAR (Meteorological Aerodrome Report)

A standardised format for reporting current weather conditions at an airport, including wind, visibility, weather phenomena, clouds, temperature, dewpoint, and pressure. See: METAR & Weather

Minimums

The lowest altitude (DA, DH, or MDA) and visibility at which a pilot may descend on an instrument approach. If minimums are not met, the approach must be abandoned.

Mode S

An advanced secondary surveillance radar (SSR) mode that interrogates each aircraft individually by its unique 24-bit address, reducing frequency congestion and enabling data link.

MSA (Minimum Sector Altitude)

The lowest altitude that provides a minimum clearance of 300 m (1,000 ft) above all obstacles within a specified sector around a navigation aid or waypoint.

MSL (Mean Sea Level)

The average sea surface level, used as the reference datum for measuring elevation and altitude in aviation. See also AMSL.

N

Nautical Mile (NM)

A unit of distance used in aviation and maritime navigation, equal to one minute of latitude or approximately 1,852 metres (6,076 ft). See: Navigation

NDB (Non-Directional Beacon)

A ground-based radio transmitter that emits a signal in all directions, used with an ADF receiver to determine bearing to the beacon. See: Navigation

NOTAM (Notice to Air Missions)

A published notice containing information on the establishment, condition, or change in any aeronautical facility, service, procedure, or hazard that is essential for flight safety.

Non-Precision Approach

An instrument approach that provides lateral guidance only (no electronic glideslope), such as VOR, NDB, or LNAV approaches. The pilot descends in steps to the MDA. See: Approach & Landing

O

OAT (Outside Air Temperature)

The ambient static air temperature outside the aircraft, used in performance calculations, icing assessment, and deriving true airspeed from calibrated airspeed.

OBS (Omni Bearing Selector)

The rotatable course-setting knob on a VOR indicator that allows the pilot to select a desired radial for navigation. See: Navigation

Octa

A unit of cloud cover measurement representing one eighth of the sky. Cloud cover is reported in oktas from 0 (clear) to 8 (overcast) in METAR reports. See: METAR & Weather

Overshoot

To fly beyond a planned turning point or extended runway centreline, or an alternative term for a go-around in some regions.

PAPI (Precision Approach Path Indicator)

A system of lights alongside the runway that provides visual glidepath guidance, showing red and white combinations to indicate if the aircraft is on, above, or below the correct approach angle. See: Approach & Landing

P

PAN PAN

The international radiotelephony urgency signal, spoken three times, indicating that the aircraft has a condition requiring assistance but is not in immediate danger. See: Emergency Procedures

Payload

The revenue-generating load carried by an aircraft, including passengers, baggage, and cargo. Maximum payload is limited by structural weight limits and available fuel.

PIC (Pilot in Command)

The pilot designated as having final authority and responsibility for the operation and safety of the flight. The PIC is the ultimate decision-maker on board.

Pitot Tube

A forward-facing probe that measures the total (ram) air pressure to determine indicated airspeed. Blockage causes erroneous airspeed readings.

POH (Pilot's Operating Handbook)

The manufacturer-approved document containing operating limitations, procedures, performance data, and systems descriptions for a specific aircraft type.

Precision Approach

An instrument approach that provides both lateral and vertical guidance to the runway, such as an ILS or GLS approach. See: Approach & Landing

Pressure Altitude

The altitude indicated when the altimeter is set to the standard datum of 1013.25 hPa (29.92 inHg). Used for flight level assignment above the transition altitude.

Prohibited Area

Airspace of defined dimensions where flight is completely forbidden for security or national defence reasons.

Q

QDM

The magnetic heading to steer to reach a station, assuming zero wind. Provided by ATC or determined by the aircraft's ADF.

QDR

The magnetic bearing of the aircraft from a station. It is the reciprocal of the QDM.

QFE

The atmospheric pressure at aerodrome elevation. When set on the altimeter, the instrument reads height above the aerodrome.

QNE

The indicated altitude when the altimeter is set to the standard pressure setting of 1013.25 hPa (29.92 inHg). Used for flight level readings.

QNH

The atmospheric pressure adjusted to mean sea level. When set on the altimeter, the instrument reads altitude above mean sea level.

R

Radial

A magnetic bearing extending outward from a VOR station. An aircraft on the 270 radial is due west of the station. See: Navigation

Radio Altimeter (Radar Altimeter)

An instrument that measures the aircraft's precise height above the terrain directly below by timing the return of a radio signal bounced off the ground.

Restricted Area

Airspace where flight is restricted due to hazardous activities (e.g., military exercises, weapons firing). Entry requires specific permission.

RNAV (Area Navigation)

A method of navigation that permits aircraft to fly any desired path within the coverage of ground or space-based navigation aids, rather than flying directly between them. See: Navigation

RNP (Required Navigation Performance)

An RNAV specification that includes on-board performance monitoring and alerting capability, ensuring the aircraft stays within a defined lateral accuracy.

Runway

A defined rectangular area on an aerodrome prepared for the landing and take-off of aircraft, designated by a two-digit number based on its magnetic heading divided by 10.

RVR (Runway Visual Range)

The distance over which a pilot on the centreline of the runway can see the runway surface markings or lights, measured by instruments near the runway. Used for low-visibility operations.

S

SID (Standard Instrument Departure)

A published IFR departure procedure providing a transition from the runway to the en-route structure, reducing radio communication and ensuring obstacle clearance.

Sigmet (Significant Meteorological Information)

A weather advisory for significant weather hazards affecting all aircraft, including severe turbulence, volcanic ash, and severe icing. See: Meteorology

Slats

Movable surfaces on the leading edge of the wings that extend to increase the wing's camber and delay stall onset at high angles of attack.

Slip

A manoeuvre where the aircraft is deliberately flown in an uncoordinated state (yaw without turn) to increase drag or correct for crosswind during approach.

Spoilers

Panels on the wing's upper surface that deploy to disrupt airflow, reducing lift and increasing drag. Used during descent, after touchdown, and for roll control on some aircraft.

Squawk

A four-digit transponder code assigned by ATC to identify an aircraft on radar. Special codes include 7700 (emergency), 7600 (comms failure), and 7500 (hijack). See: ATC Phraseology

Stall

An aerodynamic condition in which the wing exceeds its critical angle of attack, causing a sudden reduction in lift. A stall can occur at any airspeed and any attitude.

STAR (Standard Terminal Arrival Route)

A published IFR arrival procedure providing a transition from the en-route structure to a point from which an instrument approach can begin.

Static Port

An opening on the aircraft fuselage that senses ambient (static) air pressure, feeding the altimeter, airspeed indicator, and vertical speed indicator.

Stopway

A defined rectangular area beyond the end of a runway prepared as a suitable area for an aircraft to decelerate in the event of an abandoned take-off.

SELCAL (Selective Calling)

A system that alerts a specific aircraft's crew to an incoming HF or VHF radio call by transmitting a unique four-tone code, allowing the crew to reduce audio monitoring fatigue on long flights.

Standard Rate Turn

A turn at a rate of 3 degrees per second, completing a 360-degree turn in two minutes. Used as the standard for instrument flight holding patterns and procedure turns.

T

TAS (True Airspeed)

Calibrated airspeed corrected for air density (altitude and temperature). TAS increases with altitude for a given indicated airspeed.

TAF (Terminal Aerodrome Forecast)

A weather forecast issued for a specific aerodrome covering a period of 24 or 30 hours, using the same codes as METAR. See: METAR & Weather

Taxiway

A defined path on an aerodrome for the surface movement of aircraft, connecting runways to aprons, gates, and other facilities.

TCAS (Traffic Collision Avoidance System)

An airborne system that interrogates nearby transponders to detect potential collisions, issuing traffic advisories (TA) and resolution advisories (RA) with vertical escape manoeuvres.

Threshold

The beginning of the portion of the runway usable for landing, typically marked by white threshold markings and sometimes by green threshold lights.

Thrust

The forward force produced by the aircraft's engines (jet thrust or propeller thrust) that overcomes drag and propels the aircraft through the air.

Touch and Go

A training manoeuvre in which the aircraft lands on the runway and immediately applies power to take off again without coming to a full stop.

Track

The actual path of the aircraft over the ground, expressed as a bearing from north. Track differs from heading by the wind correction angle. See: Navigation

Traffic Pattern (Circuit)

The standard rectangular flight path around a runway, consisting of upwind, crosswind, downwind, base, and final legs, used for orderly arrival and departure of VFR traffic.

Transition Altitude (TA)

The altitude at or below which vertical position is expressed as altitude (with QNH set) and above which it is expressed as flight levels (with standard pressure set).

Transition Level (TL)

The lowest flight level available for use above the transition altitude. The layer between transition altitude and transition level is the transition layer.

Transponder

An airborne electronic device that transmits a coded signal when interrogated by radar, providing identification and altitude information to ATC.

Trim

The adjustment of aerodynamic surfaces (trim tabs) to relieve control pressures, allowing the aircraft to maintain a desired attitude hands-off.

True Airspeed

See TAS. The actual speed of the aircraft through the surrounding air mass, corrected for altitude and temperature from calibrated airspeed.

Turbulence

Irregular air motion caused by atmospheric instability, wind shear, jet streams, mountains, or convective activity. Categorised as light, moderate, severe, or extreme. See: Meteorology

U

Uncontrolled Airspace

Airspace (Class G) where ATC does not exercise any control authority. Pilots are responsible for their own separation from other traffic and terrain. See: Airspace Classification

Unicom

A non-government air-to-ground radio communication facility at uncontrolled airports, providing advisory information such as wind and runway in use.

UTC (Coordinated Universal Time)

The primary time standard used in aviation worldwide, eliminating confusion from different time zones. Also referred to as Zulu time.

Upwind

The leg of a traffic pattern flown in the same direction as landing, directly over or parallel to the runway. Also refers to the direction from which the wind is blowing.

V

V1 (Takeoff Decision Speed)

The speed during take-off beyond which the pilot should continue the take-off even if an engine failure is recognised. Below V1, the take-off should be rejected.

V2 (Takeoff Safety Speed)

The minimum speed that must be achieved by the time the aircraft reaches 35 ft above the runway after an engine failure at V1, ensuring adequate climb performance.

Va (Maneuvering Speed)

The maximum speed at which full or abrupt control deflection can be applied without risk of structural damage. Decreases with reduced aircraft weight.

VASI (Visual Approach Slope Indicator)

A system of lights near the runway providing visual descent guidance, showing red below the glidepath and white above, to assist pilots with approach angle. See: Approach & Landing

VFR (Visual Flight Rules)

A set of regulations that permit pilots to operate by visual reference to the ground and other aircraft, provided weather conditions meet specified minimums for visibility and cloud clearance.

VMC (Visual Meteorological Conditions)

Weather conditions equal to or better than the specified minimums for VFR flight, generally expressed in terms of visibility and distance from cloud.

VNE (Velocity Never Exceed)

The maximum speed that should never be exceeded in any phase of flight. Marked as a red line on the airspeed indicator.

VNAV (Vertical Navigation)

An FMS or RNAV function that provides vertical guidance along a computed descent or climb path, optimising fuel efficiency and meeting altitude constraints. See: Approach & Landing

VOR (VHF Omnidirectional Range)

A ground-based radio navigation aid that transmits 360 radials, allowing aircraft with a VOR receiver to determine their magnetic bearing from the station. See: Navigation

Vr (Rotation Speed)

The speed during take-off at which the pilot begins to raise the nose (rotate) to achieve a positive rate of climb.

Vref (Reference Landing Speed)

The threshold speed used as a reference for landing, typically 1.3 times the stall speed in the landing configuration. The target speed for crossing the runway threshold.

Vx (Best Angle of Climb Speed)

The speed that produces the greatest altitude gain per unit of horizontal distance, used for clearing obstacles after take-off.

Vy (Best Rate of Climb Speed)

The speed that produces the greatest altitude gain per unit of time, used for normal climb to reach cruise altitude efficiently.

W

Waypoint

A predetermined geographical position defined by latitude/longitude coordinates, used for RNAV navigation. Waypoints can be named (five-letter designators) or user-defined. See: Navigation

Weight

The force of gravity acting on the aircraft. Key weight values include MTOW (Maximum Takeoff Weight), MLW (Maximum Landing Weight), and ZFW (Zero Fuel Weight).

Wind Correction Angle (WCA)

The angle between the desired track and the heading needed to maintain that track, applied to compensate for crosswind drift. See: Navigation

Wind Shear

A sudden change in wind speed and/or direction over a short distance, particularly dangerous during take-off and landing. Can be associated with thunderstorms, fronts, and low-level jets. See: Meteorology

Wingspan

The distance from one wingtip to the other, measured in a straight line. Wingspan is a key factor in determining wake turbulence category and parking requirements.

Wake Turbulence

Disturbed air left behind an aircraft in flight, caused by wingtip vortices. Particularly hazardous behind heavy aircraft during take-off and landing; separation minima are applied by ATC.

X

X-ray (Phonetic)

The ICAO/NATO phonetic alphabet word for the letter X, pronounced "ECKS-ray". Used in aviation radio communications to avoid ambiguity. See: ICAO Alphabet

Y

Yankee (Phonetic)

The ICAO/NATO phonetic alphabet word for the letter Y, pronounced "YANG-key". See: ICAO Alphabet

Yaw

Rotation of the aircraft about its vertical (normal) axis, causing the nose to move left or right. Controlled primarily by the rudder pedals.

Yoke

The control column in the cockpit used to command pitch (fore/aft) and roll (left/right). Some aircraft use a sidestick instead of a traditional yoke.

Z

Zero Fuel Weight (ZFW)

The total weight of the aircraft and its contents excluding usable fuel. Maximum ZFW is a structural limit that prevents excessive bending loads on the wing roots.

Zulu Time

The aviation term for Coordinated Universal Time (UTC), denoted by the letter Z. All flight plans, METARs, NOTAMs, and ATC communications use Zulu time to ensure a single global time reference.