Aviation Glossary

An A Check is the lightest scheduled maintenance inspection performed on a commercial aircraft, typically every 400–600 flight hours or 1–2 months, whichever comes first. It takes 6–24 hours and is usually carried out overnight at the airline's base or at a line maintenance facility.

A-CDM is an operational framework, developed by Eurocontrol, in which airport operators, airlines, ground handlers, and air traffic control share real-time data on each flight's turnaround so they can jointly optimize aircraft turnaround and departure sequencing.

ACARS (Aircraft Communications Addressing and Reporting System) is the digital datalink system that transmits short text messages between aircraft and ground stations. It automates the reporting of flight events — out, off, on, in (OOOI times) — and enables two-way digital communication between cockpit and operations.

An ADL (Additions and Deletions List) is the update message transmitted after the initial PNL to communicate last-minute passenger list changes — late check-ins, no-shows and additional passengers — to the ground handling agent, keeping the list current until gate closure.

ADS-B (Automatic Dependent Surveillance — Broadcast) is the surveillance technology in which aircraft automatically broadcast their GPS-derived position, altitude, speed and identification to ground stations and other aircraft. It is the successor to radar-based surveillance and forms the backbone of modern air traffic management.

The IATA Airport Handling Manual (AHM) is the industry's standard reference for ground handling policies and standard messaging, used by airlines, ground handlers, and airports worldwide to keep turnaround and cargo procedures consistent.

AIDX is IATA's XML-based global messaging standard for exchanging flight data — such as schedules, operational times, and disruption information — between airlines, airports, and other third parties, developed as a modern, structured alternative to legacy Type B messaging.

The AOCC is an airline's centralized, around-the-clock facility that monitors the day's flight operations in real time and makes the operational decisions needed to manage delays, diversions, and the reassignment of crews and aircraft.

An AODB (Airport Operational Database) is the central data hub that aggregates, stores and distributes all flight-related operational data at an airport — schedules, slot allocations, actual movement times, resource assignments and flight status — serving as the single source of truth for airport systems.

APIS (Advance Passenger Information System) is the data system and legal framework requiring airlines to transmit passenger passport and identity information to the border security authorities of the destination country prior to departure. It is governed by ICAO Doc 9944 and national legislation.

An APU is a small, self-contained gas turbine — typically mounted in the tail — that provides electrical power, compressed air and main-engine starting capability while an aircraft is on the ground, without needing ground power or the main engines running.

ATPCO (Airline Tariff Publishing Company) is the industry-owned data company that collects, validates and distributes airline fare and rule data to GDS platforms, pricing engines and fare management systems. It is the central repository for published airfares worldwide.

An airline alliance is a formal, long-term partnership between separately-owned airlines that coordinate frequent-flyer reciprocity, codesharing, lounge access and connecting service, without merging — the three global alliances are Star Alliance, oneworld and SkyTeam.

Ancillary revenue is income airlines earn from products and services sold beyond the base airfare — such as baggage fees, seat selection, priority boarding, and onboard sales — and it is a core pillar of low-cost carrier business models.

A B Check is a scheduled maintenance inspection historically performed every 6–8 months, taking 1–3 days and covering more detailed systems inspections than an A Check. Note: B Check as a distinct maintenance level has been phased out by many modern aircraft programmes and OEMs, with its tasks absorbed into enhanced A Check or C Check packages.

BCBP (Bar Coded Boarding Pass) is the IATA standard that defines the data format for barcoded boarding passes. Whether on paper or mobile device, it encodes passenger and flight data in a 2D barcode (PDF417 or Aztec) readable by gate scanners, SBD units and kiosk systems.

A BHS (Baggage Handling System) is the automated conveyor, sorting and screening infrastructure that transports checked baggage from check-in acceptance points through security screening to the correct aircraft loading area or baggage claim belt.

A BRS (Baggage Reconciliation System) is the security system that cross-references gate boarding data against checked-baggage records to identify passengers whose bags are on board but who have not presented at the gate. Mandatory for all international flights under ICAO and EU regulations.

The BSP (Billing and Settlement Plan) is the IATA-managed financial settlement system through which travel agents collect and remit ticket sales proceeds to airlines. It simplifies and centralises the financial relationship between agents and multiple carriers through a single reporting, billing and settlement process.

A baggage tag is the barcoded, machine-readable label attached to checked luggage at check-in, built around a unique IATA-standardized 10-digit "license plate" number that every automated Baggage Handling System (BHS) reads to sort, load, transfer and track a bag from check-in to arrival.

Biometric passenger processing uses physiological identifiers — primarily facial recognition — to verify a traveller's identity at airport touchpoints: check-in, bag drop, lounge access, boarding gate and border control, replacing or supplementing the manual document and boarding pass check.

The "black box" refers to the two crash-hardened flight recorders every commercial aircraft carries — the Flight Data Recorder (FDR), capturing flight parameters, and the Cockpit Voice Recorder (CVR), capturing cockpit audio — both painted bright orange despite the name, and built to survive the conditions of a crash.

Block time (also block-to-block time) is the total elapsed time from the moment an aircraft leaves the departure gate (off-block) to the moment it arrives at the destination gate (on-block). It includes taxi, flight time and any airborne holding, and is the basis for schedule planning, crew duty calculation and airline cost accounting.

A C Check is a comprehensive scheduled base maintenance inspection performed approximately every 20–24 months or 6,000 flight hours, requiring 1–2 weeks in a maintenance hangar. It covers in-depth structural inspection, system overhaul and accumulated deferred maintenance.

CIQ (Customs, Immigration, Quarantine) refers to the three separate government control functions that international passengers, crew, and goods pass through when entering or, in some countries, leaving a country by air.

A CRS (Central Reservation System) is the core module within a PSS that manages an airline's flight inventory, schedules and reservations. It controls seat availability, booking classes and fare availability in real time across all distribution channels.

CUPPS (Common Use Passenger Processing Systems) is the IATA standard for shared agent-operated passenger-processing positions such as check-in desks and boarding gates. It succeeded the legacy CUTE standard, while CUSS remains the complementary standard for passenger-operated self-service devices.

CUSS (Common Use Self-Service) is the IATA standard that enables passengers to check in at shared self-service kiosks serving multiple airlines. A single physical kiosk can run check-in applications from different carriers.

CUTE (Common Use Terminal Equipment) is the IATA standard that allows airport check-in counters, gate terminals and associated equipment to be shared by multiple airlines, eliminating the need for each carrier to maintain dedicated hardware.

A codeshare is a commercial arrangement in which two airlines share the same physical flight: one airline (the operating carrier) operates the aircraft while another (the marketing carrier) sells seats on the flight under its own flight number and IATA code.

A D Check is the most comprehensive and expensive scheduled aircraft maintenance event, performed every 6–12 years. The aircraft is essentially stripped to its airframe for complete structural inspection, taking 4–6 weeks and costing $4–6 million or more for a widebody aircraft.

A Departure Control System (DCS) is the operational software used by airlines to manage check-in, seat assignment, boarding pass issuance and flight capacity from the check-in counter through to gate departure.

DEPA is the IATA SSR code designating a deportee travelling under escort — an immigration officer or authorised personnel — accompanying the individual on the return flight. The escort remains with the passenger from boarding through to arrival at the destination.

DEPU is the IATA SSR code for a deportee or person being removed travelling without an escort officer. The airline and destination authority are notified of the passenger's status; handling relies on airline staff awareness and coordination rather than a dedicated escort.

The IATA Dangerous Goods Regulations (DGR) is the industry-standard manual for classifying, packaging, labeling, and documenting hazardous materials shipped by air, built on the ICAO Technical Instructions that member states apply as regulation.

De-icing removes existing frost, ice or snow from an aircraft before departure, while anti-icing separately protects a cleaned surface from new contamination for a defined holdover time, using four standardised fluid types (I–IV) matched to weather conditions and aircraft type.

A diversion is when a flight is redirected to land at an airport other than its originally planned destination, typically because of weather, a medical emergency, a mechanical issue, or another operational reason.

A dry lease is an arrangement in which an aircraft owner leases out the aircraft alone, without crew, maintenance, or insurance — the lessee supplies these and operates the aircraft under its own Air Operator Certificate (AOC).

Duty free refers to goods sold to international travelers, typically in airport retail areas past security or aboard aircraft, without certain import duties or taxes that would otherwise apply, subject to rules that vary by country and destination.

An Electronic Flight Bag (EFB) is a portable or installed electronic device that gives flight crews access to charts, manuals, checklists, and performance calculations, replacing the paper flight bag traditionally carried by pilots.

ETA (Estimated Time of Arrival) is the current best estimate of when an aircraft will touch down or arrive on stand at the destination airport. It updates continuously based on actual departure time, airspeed, wind and routing, and is distinct from the scheduled arrival time (STA).

ETD (Estimated Time of Departure) is the current best estimate of the time at which an aircraft will push back from the gate or leave the stand. It is a dynamic value that updates as operational conditions change, and is distinct from the scheduled departure time (STD).

ETOPS is the certification framework that allows twin-engine airliners to fly routes a set number of minutes away from the nearest diversion airport on one engine, replacing the older blanket 60-minute rule and enabling twin-engine jets on long overwater and remote routes.

The eAWB is the electronic version of the paper Air Waybill — the contract of carriage and receipt for goods in air cargo — transmitted as structured data instead of a printed document, under IATA's e-freight modernization program.

An eGate (Automated Border Control Gate) is the self-service border crossing technology that uses biometric verification — typically facial recognition or fingerprint — to automate the passport and identity check at border control, enabling eligible travellers to cross without interacting with a border officer.

An FFP (Frequent Flyer Programme) is an airline loyalty scheme that rewards passengers with miles or points for flights and partner purchases. Accumulated miles can be redeemed for award tickets, upgrades and other benefits, while tier status unlocks priority services.

A FIDS (Flight Information Display System) is the airport information technology system that collects, processes and displays real-time flight status information — departures, arrivals, gate assignments, delays and cancellations — on screens throughout the terminal.

The Flight Management System (FMS) is an onboard avionics computer that integrates navigation, flight planning, and aircraft performance data so the crew can program and fly a route with optimized fuel use, speed, and altitude from takeoff to landing.

A fare basis code is the alphanumeric code printed on an airline ticket that identifies the exact fare product purchased, including its booking class (RBD) and the specific rules — such as refundability, minimum or maximum stay, and seasonality — that apply to it.

Fly-by-wire is a flight control technology in which computers interpret the pilot's or autopilot's control inputs and send electrical signals to actuators that move the control surfaces, replacing the mechanical cables, rods, and hydraulic linkages used in traditional flight control systems.

A GDS (Global Distribution System) is the technology platform through which travel agents and online booking tools access real-time flight inventory, fares and availability from multiple airlines simultaneously. Amadeus, Sabre and Travelport are the three dominant GDS providers.

GNSS (Global Navigation Satellite System) is the general term for satellite-based positioning systems used in aviation, of which GPS, operated by the United States, is one implementation alongside others such as GLONASS, Galileo, and BeiDou.

GPWS (Ground Proximity Warning System) and its enhanced successor EGPWS are onboard systems that alert pilots when the aircraft is at risk of colliding with terrain, helping prevent controlled-flight-into-terrain (CFIT) accidents.

GSE refers to the vehicles and equipment used to service an aircraft during turnaround, including pushback tugs, belt loaders, catering trucks, fuel bowsers, and de-icing vehicles.

A go-around is a routine, deliberate manoeuvre in which a crew discontinues an approach and climbs away instead of landing, triggered by anything from an unclear runway to an unstabilised approach — a planned, trained-for outcome rather than an emergency.

Ground handling encompasses all services provided to an aircraft between arrival and departure — passenger handling, baggage, ramp services (fuelling, towing, de-icing), cargo, catering, cleaning and technical support — typically provided by a specialised ground handling company contracted by the airline.

A Heavy Maintenance Visit (HMV) is a scheduled base maintenance event in which an aircraft is withdrawn from service and taken to a hangar for deep structural inspection, system overhaul and modification work that cannot be performed during line maintenance. C Checks and D Checks are the primary heavy maintenance events.

An ILS (Instrument Landing System) is the precision radio navigation system that guides aircraft to the runway during low-visibility approaches. It provides lateral guidance (localiser) and vertical guidance (glideslope) to the aircraft's instruments, enabling landings in weather conditions below visual minima.

ILS approach categories (CAT I, II, IIIA, IIIB, IIIC) classify precision instrument approaches by the minimum decision height and visibility or runway visual range at which a crew may continue toward landing, based on ground equipment, aircraft capability, and crew qualification.

An INAD (Inadmissible Passenger) is a traveller refused entry to a country by its immigration authority and returned to the point of embarkation or another country. Airlines are legally and financially responsible for the deportation of passengers they carried who were found to be inadmissible at the destination.

IOSA is IATA's internationally recognized audit program that evaluates an airline's operational management and safety control systems across eight operational areas, and which every IATA member airline must pass and renew every two years.

IROPS is airline shorthand for significant, unplanned disruptions to the flight schedule — caused by events such as severe weather, IT system outages, strikes, or widespread mechanical issues — along with the recovery processes airlines use to restore normal operations.

The inflight connectivity ecosystem is the layered supply chain that delivers Wi-Fi and networked digital services inside an aircraft cabin — spanning GEO, MEO and LEO satellite operators, the service providers and platforms that manage multi-orbit access, the antenna and terminal manufacturers who put hardware on the aircraft, and the onboard networking systems that turn a satellite signal into a working seatback or personal-device connection.

An interline agreement is a commercial arrangement between two or more airlines that allows passengers to travel on a single ticket across the networks of all participating carriers, with through-checked baggage and mutual recognition of disruption obligations.

A jet bridge (also called a passenger boarding bridge or jetway) is the enclosed, moveable connector linking an airport terminal gate to the aircraft door, allowing passengers to board and disembark without exposure to the elements or the ramp environment.

Juliet is the ICAO phonetic alphabet code word for the letter J. Spelled with a double-t (Juliett in ICAO documentation) to ensure non-English speakers stress the second syllable. Used in callsigns, registrations and any aviation radio communication requiring the letter J.

Kilo is the ICAO phonetic alphabet code word for the letter K. It is also the standard aviation unit prefix for thousands — kilofeet (altitude), kilograms (weight) — making K one of the most functionally versatile letters in aviation communications.

Line maintenance covers all aircraft maintenance tasks performed between scheduled flights — pre-flight inspections, transit checks, overnight checks and minor defect rectification — to keep the aircraft in continuous service without hangar withdrawal.

Passenger load factor is the percentage of available seat kilometres (ASKs) occupied by revenue passengers, expressed as revenue passenger kilometres (RPKs) divided by ASKs. It is the primary capacity utilisation metric for airlines and a key indicator of commercial performance.

MCT (Minimum Connecting Time) is the shortest transfer time in which a passenger can safely make a connecting flight at a given airport without missing the onward departure. Values are set by IATA and airport operators and vary by transfer type (domestic-domestic, international-domestic, etc.).

MEDA is the IATA SSR code designating a passenger with a medical condition that may affect the flight or require special handling. It triggers a medical clearance process and notifies crew and ground staff to provide appropriate assistance.

The MEL is the airline-specific, regulator-approved list defining which aircraft equipment may be inoperative on a given flight and under what conditions, derived from and never more permissive than the manufacturer's Master Minimum Equipment List (MMEL).

MRO (Maintenance, Repair and Overhaul) is the industry term for the full spectrum of aircraft maintenance activities — from routine overnight checks to complete structural overhauls — carried out to keep aircraft airworthy and compliant with regulatory requirements.

MTOW is the certified maximum total weight — aircraft, fuel, passengers, baggage and cargo combined — at which an aircraft is permitted to attempt takeoff, distinct from the separate maximum ramp, landing and zero fuel weight limits that govern other phases of flight.

NDC (New Distribution Capability) is the IATA XML-based communication standard that enables airlines to distribute rich content — ancillaries, personalised offers, dynamic pricing — directly to travel agents and booking tools without routing through traditional GDS intermediaries.

NFC (Near Field Communication) is the short-range wireless communication technology (range up to 10cm) used at airports for contactless boarding pass scanning, mobile payment and identity verification. It enables passengers to board aircraft by tapping a smartphone or wearable against an NFC reader.

A NOTAM (Notice to Airmen, now officially Notice to Air Missions) is a notice distributed by official channels to alert pilots and flight operations personnel to information essential for safe flight — airspace restrictions, navigational aid outages, runway closures and hazardous conditions.

A no-show is a passenger who holds a confirmed reservation for a flight but fails to check in or present themselves for boarding, without cancelling the booking in advance.

An O&D pair is a passenger's true origin airport and final destination airport, treated as a single unit of travel demand regardless of how many connecting flights or which airlines are used to complete the journey.

OSI (Other Service Information) is a free-text informational note added to a PNR for the airline's awareness. Unlike an SSR, it requires no action from the airline — it carries contextual information such as VIP status, programme membership or contact notes.

OTP (On-Time Performance) is the key performance indicator measuring the percentage of flights that depart or arrive within a defined threshold — typically 15 minutes — of their scheduled time. It is the primary punctuality metric used by airlines, airports and regulators.

Overbooking is the practice of selling more tickets than an aircraft has seats, anticipating no-shows; when too many booked passengers show up, airlines must first seek volunteers before resorting to involuntary denied boarding, which triggers statutory compensation in most major markets.

A PNL (Passenger Name List) is the pre-departure message transmitted by the airline to the ground handling agent, handling company or partner airline, listing all passengers on the flight with their names, seat numbers and SSR information.

A Passenger Name Record (PNR) is the data structure that holds all information relating to a passenger's booking — identity, flight segments, ticket, special service requests (SSR) and contact details — under a single record identified by a unique six-character reference code.

PRM (Passenger with Reduced Mobility) is the umbrella term for travelers who need assistance moving through the airport or aircraft, with the specific type of help recorded using standardized wheelchair SSR codes: WCHR, WCHS, and WCHC.

A Passenger Service System (PSS) is the central software platform airlines use to manage reservations, inventory, ticketing and passenger services. It forms the data layer on which the DCS and other operational systems depend.

The ICAO Phonetic Alphabet is the standardised set of 26 code words — Alpha through Zulu — assigned to each letter of the Latin alphabet to ensure unambiguous voice communication over radio between pilots, controllers and ground personnel worldwide.

QNH is the altimeter setting that, when applied to the aircraft's barometric altimeter, causes it to indicate the aircraft's altitude above mean sea level (AMSL). It is derived from the local atmospheric pressure reduced to sea level and is the standard altimeter setting used below the transition altitude.

Quebec is the ICAO phonetic alphabet code word for the letter Q. In aviation, Q also appears as a prefix in the Q-code system — a set of three-letter codes (QNH, QFE, QNE) historically used in radio communications and still standard in altimeter settings and weather reports.

An RBD (Reservation Booking Designator) is the single letter code — such as Y, B, M, Q or X — used in the CRS and GDS to denote a specific booking class within a cabin. Each RBD carries distinct fare, accrual and availability rules and is the mechanism through which airline yield management is operationalised.

RFID (Radio Frequency Identification) is the wireless technology used in aviation baggage handling to track bags through the airport journey. RFID baggage tags replace or complement traditional barcodes, enabling more reliable automated reading rates (99%+ vs 80–85% for barcodes) and real-time tracking throughout the BHS.

An RMS is the software platform an airline uses to implement its yield/revenue management strategy in practice, forecasting demand and controlling seat inventory and fare-class availability across booking channels to optimize revenue.

RNP and RNAV are the two families of performance-based navigation specification under ICAO's PBN framework that let aircraft fly precise, repeatable paths defined by onboard systems rather than by flying directly to and from ground-based navaids.

RVSM is the airspace standard that reduced the minimum vertical spacing between aircraft above Flight Level 290 from 2,000 feet to 1,000 feet, roughly doubling the number of usable cruise altitudes in the busiest part of the flight envelope.

SARPs are the Standards and Recommended Practices adopted by ICAO under the Chicago Convention's 19 Annexes — the mechanism by which ICAO sets binding-in-intent international aviation requirements that member states are expected to implement in their own national regulations.

A Self Bag Drop (SBD) unit is an automated baggage acceptance point where passengers who have already completed check-in can weigh and deposit their luggage without staff assistance. It is the physical complement to the CUSS kiosk check-in flow.

An SSR (Special Service Request) is the standardised IATA data field used to record passenger requests for special services — wheelchair assistance, special meals, medical support, infant bassinets — in the PNR using four-letter codes such as WCHR, VGML and MEDA.

STCR is the IATA SSR code designating a passenger who must travel lying flat on a stretcher, typically due to a medical condition or post-surgical requirement. Stretcher carriage requires removal of economy seats, special medical clearance and coordination with the airline's medical desk.

SWIM (System Wide Information Management) is the aviation data-sharing framework that enables standardised, interoperable exchange of operational information — flight data, weather, airspace, airport status — across all stakeholders in the aviation ecosystem using internet-based protocols.

An airport slot is the permission granted by a slot coordinator for an airline to use an airport's full infrastructure — runway, terminal and apron — to arrive or depart at a specific date and time. Slots are allocated at Level 3 (fully coordinated) airports where demand exceeds capacity.

Special meal codes are standardized four-letter codes airlines use to record and communicate a passenger's requested in-flight meal for religious, medical, dietary, or age-related reasons, distinct from the standard catering served to other passengers.

A squawk code is a four-digit code entered into an aircraft's transponder that identifies it to air traffic control radar, including three universally reserved emergency codes — 7500 (hijacking), 7600 (radio failure) and 7700 (general emergency).

A stopover is a deliberate, extended break in a passenger's journey at an intermediate point, typically lasting well beyond the time needed simply to change planes, before continuing to the final destination.

TCAS is an onboard system that independently tracks nearby transponder-equipped aircraft and warns the crew of a collision risk, escalating from an informational Traffic Advisory (TA) to a directive Resolution Advisory (RA) that pilots are trained to follow immediately.

TIMATIC (Travel Information Manual Automatic) is the IATA database system used by airlines and airports to verify passenger travel document requirements — visa, passport validity, health requirements and entry restrictions — at check-in and boarding, based on nationality, destination and transit points.

An aircraft turnaround is the ground process between an aircraft's arrival at stand and its subsequent departure: the coordinated sequence of deplaning, cleaning, catering, fuelling, technical inspection, baggage offload/load and boarding that must be completed within a target time to maintain schedule.

Type B messaging is the legacy store-and-forward telex-style network, carried over the SITA and ARINC (Collins Aerospace) global networks, that airlines and airports use to exchange structured, text-based operational messages such as passenger, load, and disruption data.

A ULD (Unit Load Device) is a standardised container or pallet used to consolidate cargo, mail and baggage into a single unit for efficient loading into the lower hold of wide-body aircraft. ULDs allow ground equipment to handle large quantities of freight as a single, forklift-compatible unit.

A UM (Unaccompanied Minor) is a child travelling without a parent or guardian who is enrolled in the airline's supervised unaccompanied minor programme. The airline assumes duty of care from check-in at the origin through to handover to an authorised adult at the destination.

VHF (Very High Frequency, 30–300 MHz) is the primary radio band used for air-ground voice communications in civil aviation. ATC and pilots communicate on VHF frequencies assigned by ICAO for different phases of flight — ground, tower, approach, departure and en-route.

A VOR (VHF Omnidirectional Range) is a ground-based radio navigation beacon that transmits a signal allowing aircraft to determine their radial — the magnetic bearing from the station — enabling position fixing and airway navigation. VORs form the backbone of the conventional airway system.

Wake Turbulence Category is the ICAO classification (Light, Medium, Heavy, Super) that groups aircraft by Maximum Takeoff Weight to determine the minimum following separation air traffic control must apply, since heavier aircraft generate stronger, longer-lasting wake vortices.

A waypoint is a defined geographical position — identified by a five-letter name code (e.g. LOGAN, TULIP) or a VOR/DME fix — used to define flight routes, airways, departure and arrival procedures, and to report position to ATC.

A wet lease is an aircraft leasing arrangement in which the lessor supplies the aircraft, crew, maintenance and insurance (ACMI) and retains operational control, distinct from a dry lease where the lessee supplies everything but the bare aircraft and operates it under its own certificate.

X-ray inspection is the primary security screening method for carry-on baggage and checked luggage at airports, using X-ray imaging to detect prohibited items — weapons, explosives, liquids above limits — without opening bags. Required at all commercial airports under ICAO Annex 17 and national regulations.

Yield management (revenue management) is the practice of dynamically controlling the availability and price of airline seats to maximise revenue from each flight — opening and closing booking classes (RBDs) in real time based on demand, booking pace and remaining capacity.

Zulu time is the aviation and military term for Coordinated Universal Time (UTC). All aviation operations — flight plans, ATC communications, NOTAMs, METARs and schedules — use Zulu time to eliminate confusion from time zones and daylight saving changes across global operations.