Aviation Glossary: Flight Tracking & Airline Terms

Plain-language definitions of 82 flight tracking, airline and airport terms, each with a Pakistan-focused example.

A · B · C · D · E · F · G · H · I · J · L · M · N · O · P · R · S · T · V · W

A

• ACMI: ACMI stands for Aircraft, Crew, Maintenance and Insurance: a type of lease in which the lessor provides all four.
• ADS-B: ADS-B (Automatic Dependent Surveillance–Broadcast) is a system in which an aircraft works out its own position from satellite navigation and broadcasts it, together with altitude, speed and identity, about once per second.
• Aircraft Registration: An aircraft registration is the unique code, like a car’s number plate, painted on an aircraft to show which country it is registered in.
• Airline Delay Code: An airline delay code is a standard number that airlines use to record the cause of a delay, such as late baggage, weather or air traffic control.
• Airport Slot: An airport slot is permission for an airline to land or take off at a particular airport at a particular time.
• Alternate Airport: An alternate airport is a backup airport where a flight can land if it cannot land at its destination.
• Apron: The apron is the area of an airport where aircraft are parked for boarding, loading, refuelling and maintenance.
• APU: An APU (auxiliary power unit) is a small engine, usually in the tail, that supplies electricity and air conditioning when the main engines are off.
• ASK: ASK (available seat kilometres) is a measure of an airline’s capacity: the number of seats multiplied by the distance flown in kilometres.
• ATA: ATA (actual time of arrival) is the time an aircraft really arrived, usually measured when it touched down or reached the gate.
• ATC: ATC (air traffic control) is the service that directs aircraft to keep them safely separated and moving in an orderly way.
• ATD: ATD (actual time of departure) is the time an aircraft really left, usually when it pushed back from the gate or took off.
• Autoland: Autoland is a system in which the aircraft’s autopilot lands the aircraft automatically, including the flare and rollout.

B

• Belly Cargo: Belly cargo is freight carried in the lower hold of a passenger aircraft, beneath the passengers.
• Block Time: Block time is the time from when an aircraft leaves the gate (off-blocks) to when it stops at the destination gate (on-blocks).

C

• Callsign: A callsign is the identifier a flight uses on the radio and in air traffic systems, usually the airline’s three-letter ICAO code followed by the flight number.
• CAT III: CAT III is the most demanding category of instrument landing, allowing aircraft to land in very low visibility, with runway visual range as low as about 200 m down to 50 m or less depending on the sub-category.
• Cloud Ceiling: The cloud ceiling is the height of the lowest layer of cloud that covers more than half the sky (broken or overcast).
• Codeshare: A codeshare is an arrangement where a flight operated by one airline is also sold under another airline’s flight number.
• Codeshare vs Interline: Codeshare means a flight is sold under another airline’s code; interline means airlines honour each other’s tickets without sharing flight numbers.
• Crosswind: A crosswind is wind that blows across the runway rather than along it.
• Cruise Altitude: Cruise altitude is the height at which an aircraft spends most of a flight, typically between about 31,000 and 41,000 feet for airliners.

D

• Diversion: A diversion is when a flight lands at an airport other than its planned destination.
• DME: DME (distance measuring equipment) is a ground station that tells an aircraft how far it is from the station.

E

• EASA: EASA (the European Union Aviation Safety Agency) is the European body that sets and enforces aviation safety rules in the EU and approves foreign airlines that fly there.
• ETA: ETA (estimated time of arrival) is the time a flight is currently expected to arrive.
• ETD: ETD (estimated time of departure) is the time a flight is currently expected to leave.
• ETOPS: ETOPS (extended-range twin-engine operations) is the approval that lets a two-engine airliner fly routes where the nearest suitable airport can be far away.

F

• FAA: The FAA (Federal Aviation Administration) is the United States authority that regulates civil aviation in the US.
• FIR: A FIR (flight information region) is a defined block of airspace in which a country, or a group of countries, provides air traffic and alerting services.
• Flight Dispatcher: A flight dispatcher is an airline specialist who plans a flight, checks weather and airspace, calculates fuel and monitors the flight alongside the captain.
• Flight Level: A flight level (FL) is an altitude expressed in hundreds of feet above the standard pressure level of 1013.25 hPa, for example FL350 is about 35,000 feet.
• Flight Plan: A flight plan is the document filed before a flight with the planned route, altitude, speed, fuel and alternate airports.
• Freighter: A freighter is an aircraft that carries only cargo, with no passenger cabin.
• Fuel Reserve: A fuel reserve is the extra fuel an aircraft must carry beyond the amount needed to reach its destination, to cover delays, diversions and contingencies.

G

• Go-Around: A go-around is when a pilot aborts a landing approach and climbs away to try again or divert.
• GPWS: GPWS (ground proximity warning system) is an onboard system that warns pilots when the aircraft is too close to the ground or to terrain.
• Ground Speed: Ground speed is an aircraft’s speed over the ground, in other words how quickly it is actually covering distance.

H

• Holding Pattern: A holding pattern is a racetrack-shaped loop that aircraft fly while waiting for clearance to land or continue.
• Hub and Spoke: Hub and spoke is a route network in which flights from many smaller airports (spokes) connect through one central airport (the hub).

I

• IATA: IATA (the International Air Transport Association) is the trade association of the world’s airlines, which also assigns the two-letter airline and three-letter airport codes used in ticketing.
• IATA Code: IATA codes are the short codes used by the travel industry: two letters for airlines (PK) and three letters for airports (KHI).
• ICAO: ICAO (the International Civil Aviation Organization) is the United Nations agency that sets international standards for civil aviation safety, air navigation and airport operations.
• ICAO Code: ICAO codes are the codes used by pilots, air traffic control and weather reports: three letters for airlines (PIA) and four letters for airports (OPKC).
• ILS: ILS (instrument landing system) is a ground-based radio system that guides an aircraft down to a runway using a horizontal and a vertical beam.
• Indicated Airspeed: Indicated airspeed (IAS) is the speed shown on the aircraft’s airspeed indicator, based on the pressure of the air rushing into the instrument.
• Interline: An interline agreement lets one airline sell and check baggage on tickets that include another airline’s flights, without the two airlines sharing flight numbers.

J

• Jet Bridge: A jet bridge (or boarding bridge) is a covered walkway that connects an aircraft door directly to the terminal.

L

• Load Factor: Load factor is the percentage of an airline’s seats that are filled with paying passengers.

M

• Mach Number: The Mach number is an aircraft’s speed as a fraction of the speed of sound in the surrounding air.
• MEL: An MEL (minimum equipment list) is the list of equipment that is allowed to be broken on an aircraft while it still flies, and under which conditions.
• METAR: A METAR is a routine report of the actual weather at an airport, issued in a standard coded format, usually every 30 or 60 minutes.
• MLAT: MLAT (multilateration) is a way of finding an aircraft’s position by comparing the exact time its transponder signal reaches several ground receivers.
• MSN: MSN (manufacturer serial number) is the unique number a manufacturer gives to each aircraft it builds.

N

• Narrowbody: A narrowbody (or single-aisle) aircraft has one aisle in the cabin and is used on short and medium routes.
• No-Show: A no-show is a passenger who has a booking but does not turn up for boarding and has not cancelled in advance.
• NOTAM: A NOTAM is a notice to pilots about a temporary change or hazard, such as a closed runway or restricted airspace.

O

• OOOI: OOOI stands for Out, Off, On, In: the four events that mark a flight, being pushback from the gate, takeoff, landing and arrival at the gate.

P

• PCAA: PCAA is an abbreviation commonly used for the Pakistan Civil Aviation Authority, the national body that regulates civil aviation in Pakistan and provides air navigation services.
• Pushback: Pushback is when a tug pushes an aircraft backwards away from the gate so it can taxi under its own power.

R

• Regional Jet: A regional jet is a small jet airliner, usually seating fewer than about 100 passengers, used on shorter or thinner routes.
• RPK: RPK (revenue passenger kilometres) is a measure of how much passenger traffic an airline carries: paying passengers multiplied by the distance they fly.
• RVR: RVR (runway visual range) is how far a pilot can see along the runway, measured by instruments beside it.
• RVSM: RVSM (reduced vertical separation minimum) allows aircraft to fly 1,000 feet apart vertically, instead of 2,000 feet, between about 29,000 and 41,000 feet.

S

• SID: A SID (standard instrument departure) is a published route that aircraft follow after takeoff to join the airways.
• Squawk: A squawk is a four-digit code that an aircraft’s transponder sends so air traffic control can identify it on radar.
• STA: STA (scheduled time of arrival) is the arrival time published in the airline’s timetable.
• STAR: A STAR (standard terminal arrival route) is a published route that aircraft follow from the airway down towards an airport.
• STD: STD (scheduled time of departure) is the departure time published in the airline’s timetable.

T

• TAF: A TAF (terminal aerodrome forecast) is a coded weather forecast for an airport, usually covering 24 hours or more.
• Taxiway: A taxiway is a path for aircraft to move between runways, aprons and terminals.
• TCAS: TCAS (traffic collision avoidance system) is an onboard system that warns pilots of nearby aircraft and tells them how to avoid a collision.
• Top of Descent: The top of descent is the point at which an aircraft leaves its cruise altitude and begins its descent towards the destination.
• Transition Altitude: The transition altitude is the height at which pilots change from setting their altimeter to local pressure to setting it to standard pressure.
• True Airspeed: True airspeed (TAS) is an aircraft’s actual speed through the air, corrected for altitude and temperature.
• Turboprop: A turboprop is an aircraft powered by a gas turbine engine that turns a propeller.
• Turnaround Time: Turnaround time is the time an aircraft spends on the ground between landing and its next departure.

V

• Visibility: Visibility is how far one can see horizontally in the prevailing weather, usually measured in metres or kilometres.
• VOR: A VOR (VHF omnidirectional range) is a radio beacon that tells an aircraft its bearing from the station.

W

• Wet Lease: A wet lease is an arrangement in which one airline rents an aircraft together with its crew, maintenance and insurance from another operator.
• Widebody: A widebody (or twin-aisle) aircraft has two aisles in the passenger cabin and is used mainly on long or busy routes.
• Windshear: Windshear is a sudden change in wind speed or direction over a short distance, which can make an aircraft lose or gain lift quickly.