Aviation Dictionary

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  A check – A particular type of aircraft maintenance check specified by the manufacturer of the aircraft.  Not all aircraft have the same letters for these checks, they are aircraft specific.  However, typically an A check will be done on an aircraft every 500 to 700 flying hours.  Other checks include B, C, D, IV, and W checks.  Not all are based on flying hours.  A typical B check, for example, may be after say 120 elapsed days.  C checks might be specified as every 500 days, 15 months or 6000 flying hours and so on according to manufacturer and aircraft type.  Some checks may also be in terms of number of cycles.  It is also possible to split these checks.  For example, some airlines may choose to perform 2 “half-C” checks or even 3 “third-C” checks.
  ABC Guide –
  ACARS – Equipment fitted to British Airways aircraft that detects when the aircraft has pushed back by sensing that the doors are closed and brakes are off.  At this point a message is sent out that the aircraft is off blocks.  This system is open to abuse in that it is possible to close doors and release brakes but stay on stand.  This makes the flight appear to have departed punctually but in fact still occupies resources when it shouldn’t and takes off late.
  Accept (c.f. offer) ­–
  ACS – One of a set of IATA defined standard variations on the aircraft type that are given a special subtype code to uniquely define the subtype.  For example an Airbus Industrie A340‑200 has an aircraft subtype of “342” and the A340-300 is subtype “343”.  The full list of available aircraft subtypes and their subtype codes are given in the SSIM Manual.
  Action code – The code used by the system to tell the vendor what ACTION should be taken on the
  segment or SSR (request, cancel, etc.).
  Actual Time of Arrival – The time at which a craft arrives at a specified point at a destination.
  Actual Time of Departure – The time of leaving a specified point at a place.
  Ad-hoc schedule – A variation, addition or cancellation from the basic schedule of one or more flights on single dates.
  Ad-hoc Schedule Message –
  Administrating carrier – The airline which controls the operation of a flight.
  AHC – Airport Handling Committee (IATA)
  AHM – Airport Handling Manual (IATA).
  Air Traffic Control – the ground-based personnel and equipment concerned with controlling and monitoring air traffic within a particular area.
  Air Transport Association of America – (ATA)
  Air Transport Movement – Landings or take-offs by aircraft engaged in the commercial carriage of passengers, cargo or mail.
  Air waybill – air waybill (AWB) or air consignment note is a receipt issued by an international airline for goods and an evidence of the contract of carriage, but it is not a document of title to the goods. Hence, the air waybill is non-negotiable.
  Airborne – moving or being carried through the air
  Aircraft – A transport vehicle which is certified as airworthy by a competent aeronautical authority.  NB: as defined by IATA, this definition “may include surface vehicles, the bookings and traffic handling for which are dealt with in a similar manner to that used for aircraft”.
  Aircraft configuration – Also known as seating configuration.  Planned utilisation layout of aircraft interior space.  This can include the need for seat-occupying interpreters and long haul crew rest seats, so the saleable seats are therefore the remainder.
  Aircraft on Ground.  Maintenance term for those aircraft available to them on the ground and accessible to them for maintenance.
  Aircraft fleet – May refer to the complete complement of an airline’s fleet, or a subset defined by: range (e.g. long haul fleet, mid-range fleet, short haul fleet); aircraft type (e.g. 747 fleet, A310 fleet); or function
  Aircraft registration – (also known as tail allocation)
  Aircraft type – One of a set of IATA defined standard types of aircraft that are given a General Designator to uniquely define the type.  For example a McDonnell Douglas MD11 passenger aircraft has a General Designator of M11.  The mixed configuration MD11 is a different type with a General Designator of M1M.  The full list of available aircraft types and their General Designators are given in the SSIM Manual..
  Aircraft subtype – One of a set of IATA defined standard variations on the aircraft type that are given a special subtype code to uniquely define the subtype.  For example an Airbus Industry A340‑200 has an aircraft subtype of “342” and the A340-300 is subtype “343”.  The full list of available aircraft subtypes and their subtype codes are given in the SSIM Manual.
  Aircraft version – Defines a specific seating configuration of a particular aircraft type.
  Aircraft utilisation –
  Airline designator – An IATA standard two or three letter identifier that uniquely defines an airline.
  Airport advice procedure – see airport clearance procedure.
  Airport authority –
  Airport clearance procedure – ... (also known as airport advice procedure)
  Airport co-ordinator – … (also known as co-ordinator)
  AMADEUS – A particular passenger reservation system widely used by travel agents in Europe (compare GALILEO).
  AOC – see …
  AOG – see Aircraft On Ground.
  AIRIMP – Reservations Interline Messaging Procedures – Passenger (ATC/IATA)
  Airline –
  Airline designator – The two or three character IATA code that uniquely identifies a carrier and is most commonly used as the first part of a flight designator.
  Airworthy – An aircraft holding a current, valid C of A.
  Airspace –
  ARINC – Aeronautical Radio Incorporated.
  Arrival station – A station at which a flight leg will land.
  ASK – see Available Seat Kilometres.
  ASM – see Ad-hoc Schedule Message.
  ATA – [1] see Air Transport Association of America.
  ATA – [2] see Actual Time of Arrival.
  ATD –see Actual Time of Departure.
  ATC – see Air Traffic Control.
  ATC Passenger Committee – A committee of the ATCA.
  ATCA – Air Traffic Conference of America, now Air Transport Association of America
  ATM ­– see Air Transport Movement
  ATK – see Available Ton Kilometres
  ATZ – Air Traffic Zone.
  Aviation authority – A country’s official body responsible for all aspects of air safety. ????
  Available Seat Kilometres – For a given flight or segment of a flight, this figure is the product of the distance travelled in kilometres times the number of available passenger seats.  It is used to give an idea of the maximum passenger throughput being offered by the airline.
  Available Ton Kilometres – For a given flight or segment of a flight, this figure is the product of the distance travelled in kilometres times the number of tons of payload that could be carried.  It is used to give an idea of the maximum cargo throughput being offered by the airline.
  B check – A particular type of aircraft maintenance check specified by the manufacturer of the aircraft.  Not all aircraft have the same letters for these checks, they are aircraft specific.  However, typically an A check will be done on an aircraft every 500 to 700 flying hours.  Other checks include B, C, D, IV, and W checks.  Not all are based on flying hours.  A typical B check, for example, may be after say 120 elapsed days.  C checks might be specified as every 500 days, 15 months or 6000 flying hours and so on according to manufacturer and aircraft type.  Some checks may also be in terms of number of cycles.  It is also possible to split these checks.  For example, some airlines may choose to perform 2 “half-C” checks or even 3 “third-C” checks.
  Baggage – suitcases and bags containing personal belongings packed for travelling; luggage.
  Base (also known as ACS)
  Base stand ­– A term used by some airlines to describe an aircraft stand that is controlled by an engineering or maintenance department and as such would normally be used only for aircraft that are awaiting some sort of technical service.  In certain circumstances, base stands might also be used as off-pier stands for passenger flights at some airports.
  Base station – An airport at which the airline would maintain aircraft, and / or out of which it would operate crew.  Compare crew base and maintenance base.
  Basic schedule – Also known as a seasonal schedule.  The planned regularly operated flights of an airline. (IATA definition). This is essentially all those flights for a given IATA season that are planned via SSMs.  Ad-hoc flights (via ASMs) are not included in this definition.  For the purpose of the Functional Requirements, this is taken to include regularly operated flights during a sub season as well.
  Block time – The period of elapsed time between an aircraft pushing off blocks at the start of a flight leg and arriving on blocks at the end.  The actual block time is this period as actually operated.  For planning purposes, the block time is derived from several factors: departure airport; arrival airport; aircraft type; carrier; service type in/out; and whether of not it applies to peak time, winter or summer.
  Blocked space flight – see leased space flight.
  Blocking[s] – (also known as aircraft blockings), Blocked, Blocked off.  The task of allocating a specific period of time to an aircraft or aircraft type in order to reserve this period for a specific use of that aircraft or an aircraft of that type.  See also maintenance blockings.
  Board point – See station of embarkation.
  Body type – A categorisation of an aircraft into one of either wide bodied or narrow bodied.  (Official IATA definition???…)
  Booking – see reservation.
  Break of journey – see stopover.
  Bucket –
  Bulkhead – Rigid partition.
  Bump –
  C check –... (see A checks).
  C of A ­– see Certificate of Airworthiness.
  Cabin – A compartment where passenger seats are installed.
  Cabin crew ­– Airline staff responsible for looking after passengers in flight, more properly called flight attendants.
  Cabin refurbishment ­– A regular aircraft maintenance procedure recommended by the manufacturer during which the cabin is refurbished.
  Call sign – The unique code assigned to an aircraft that is used by its pilot to identify the aircraft to air traffic control.
  Car. – Common abbreviation for carrier.
  Cargo – Any goods carried on an aircraft and covered by an air waybill.
  Carrier – The airline responsible for any passengers, baggage, cargo or mail being carried at the point in question.
  Carrier code – see airline designator.
  Certificate of Airworthiness – (also known as C of A) A certificate issued on an aircraft after manufacture by a country’s aviation authority that certifies the aircraft to be fully safe to fly.  The certificate remains in force as long as the manufacturer’s servicing and maintenance regime has been rigidly adhered to or exceeded.  If the regime is allowed to lapse, or evidence of adherence cannot be produced, the aircraft must be re-certified by a representative of the aviation authority.
  Change of equipment en route –A scheduled change of aircraft, occurring one or more times en route, but identified by one airline designator/flight number between the station of origin and the station of final destination (also known as change of gauge en route).
  Change of gauge en route – see change of equipment en route.
  Charter flight – … (compare scheduled flight).
  Check window – The blocking pre-allocated to some sort of aircraft maintenance within which a specific tail number will be scheduled for maintenance (compare maintenance blocking).
  Check-in gate –
  Chock-on – (see/better known as on-blocks; or sometimes referred to as on-chocks)
  Chock-off – (see/better known as off-blocks; or sometimes referred to as off-chocks)
  City pair – Two cities that define a flight segment, being the passenger’s view of the flight between the station of departure and the station of final destination.
  CISC – see
  Class – Segregation of passengers according to the fare paid or facilities and services offered.  F = First, C = Coach, Y = …???
  Close-out – The final procedures that the departure-gate goes through as soon as it has closed the flight to further passengers.
  CNL – see
  CoCo – Connection Compiler
  Cockpit crew –
  Code list – An EDIFACT term for the complete set of data element values of a coded simple data element.
  Code sharing flight – (also known as code share) A generic term referring to various types of operational or commercial arrangements between two or more airlines.  See joint operation flight, leased or blocked space flight or shared airline designator flight.
  Combi – An aircraft designed or configured to take both cargo and passengers (compare full pax).
  Commercial ferry flight – A ferry flight that has been opened up to bookings and now carries fare-paying passengers.
  Commercial flight – Any flight that has been planned to carry fare-paying passengers or cargo.
  Compartment – A space designated within an aircraft for the carriage of passengers or deadload.
  Complexing – see funnel flight (also known as, starburst, W flight, Y flight)
  Component data element – An EDIFACT term for a simple data element used within a composite data element.
  Composite flight – A flight composed of two or more member flights of any type, but which is identified with an airline designator/flight number combination different from any of its member flights.
  Computerised Reservation System – The general term for any flight booking system based on computer.  Generally used to refer to the airline’s own reservation system but strictly speaking can include centralised commercial systems such as AMADEUS and GALILEO.
  Conditional – The status of a data element, or EDIFACT segment, composite data element, simple data element or component data element, marked C, which becomes mandatory under certain circumstances which have to be specified.
  Concession – see extension concession.
  Configuration – see aircraft configuration.
  Connection – (also known as transfer) the physical transfer from one flight to another (online or interline) within a reasonable time interval.
  Container – see unit load device.
  Co-ordinated airport – An airport that requires all aircraft movements to get slot clearance before a flight is scheduled to arrive at or depart from that airport (compare non-co-ordinated airport)
  COP – see trip.
  Country Code – A 2 letter code uniquely identifying a country as defined in ISO 3166.  ICAO/IATA...
  CR – see cabin refurbishment.
  Crew –
  Crew base – An airport out of which an airline operates crew.
  Crew pairing – (Also known in some airlines as crew rotation).  This is the task of matching both cockpit and cabin crews to the scheduled flights so as to ensure the appropriately skilled crews are used, while ensuring that Flight Duty Regulations are adhered to and the minimum crew costs are incurred.
  Crew roster –
  Crew rotation – see crew pairing.
  Crew tracking  –
  Crew turnaround time – ... (compare transit time, turnaround time).
  Crossflow – A situation that can arise in terminals where a stream of passengers (for example just having arrived on an inbound flight) has to cross paths in the terminal with another stream of passengers (for example going to board a departing flight) and thus causes a delay to both streams and congestion in the terminal.
  CRS – see Computerised Reservation System.
  Curfew – A period of a day during which all operations at a given station must cease (compare night ban).
  Cycle – A single take-off and landing of an aircraft.
  D check – ... (see A checks).
  D³ – (also known as DDD) see Demand Driven Dispatch.
  Data element – a sequence of alpha-numeric characters which, depending on their specific context and position, has a unique meaning, e.g. “flight designator”, “days of operation”.
  Data element separator – An EDIFACT term for a service character used to separate simple data elements or composite data elements.
  Dated schedule – Also known as a fully dated schedule.  A local term used by some airlines to describe a schedule whose flights are defined with specific dates, not just by standard weeks effective over a given date range (compare frequential schedule).
  Daylight Saving Time – ...(compare UTC).
  Daylight saving group – A term sometimes used to define a set of airports that all share a common date and time at which they would switch over to daylight saving time.
  Days of operation – The days of the week on which a flight operates.  This is often specified as a seven item string of numbers from 1 to 7 representing the days of the week (starting from Monday as 1).  Where the flight operates, the day number appears.  Where it does not operate, there is a hyphen.  So, a flight operating, say, Monday, Wednesday and Friday only would be represented by the string “1-3-5--”, and just weekends would be “-----67”.
  DCS – see Dispatch Control System
  Deadhead –
  Deadload – Anything carried on an aircraft other than passenger and crew (???) Fuel etc.?
  Delay reason – see irregularity code.
  Demand Driven Dispatch – (also known as D³) An approach to maximising revenue that relies on forecasting over and under bookings for specific flights near to the day of operation, then finds ways of re-rotating aircraft so that the aircraft are best matched to the actual expected passengers numbers in various classes.
  Departure gate –
  Dry lease – An aircraft leasing arrangement where the lessor provides only the aircraft itself and the airline is responsible for all aspects of staffing, fuelling and operating it(compare wet lease)
  Dispatch Control System –
  Dispatcher –
  Domestic flight leg – A flight between two stations to which the same ISO country code applies.
  DST – see Daylight Saving Time.
  Dummy aircraft type – An ‘invalid’ aircraft type code used where, say, an IT system demands an aircraft type in order to do a task, but the user knows it is not important and anyway cannot be defined yet.  It is common practice here to use ‘X’, as IATA don’t support that as an aircraft type.
  Duplicate leg – A single, non-operational leg of a flight that, for commercial reasons, is displayed under more than one flight number by the operating carrier, or is displayed by a different airline designator/flight number by an airline other than the operating carrier (also known as marketing leg, non-operational leg).
  ECB – EDIFACT Co-ordination Board (IATA).
  EDIFACT– Electronic Data Interchange For Administration, Commerce and Transport (United Nations).
  En route – (also known as through) Between station of origin and station of destination.
  EQT – EQuipment Type.  An ASM message type as defined in the SSIM that notifies someone that an item of equipment or aircraft type that was scheduled has changed.
  Equipment – Can mean either an aircraft type itself (see change of equipment en route, EQT) or something fitted to an aircraft.
  Estimated Time of Arrival –
  Estimated Time of Departure –
  ETA – see Estimated Time of Arrival.
  ETD – see Estimated Time of Departure.
  ETOPS – A contraction of ExTended OPerationS (see extended operations). 
  Euroslot – The European authority governing use of airspace over Europe.  Co-ordinates flight paths and airspace slot permissions across Europe, but is not responsible for airport slot allocation.
  Extended Operations – Also known as ETOPS.  This is where an aircraft that would normally never be allowed to operate further than, for example, 1 flying hour from an airport, would be fitted with special equipment that allowed to fly as far as, say, 1.5 hours away, thus offering the potential to alleviate potential routing problems.
  Extension concession  – Authorisation (from the country’s aviation authority?) to operate an aircraft for up to a certain number of hours and cycles beyond its official deadline for an A or C check.  This is normally only sought as a last resort when maintenance rotations cannot be found that will operate the flight schedule while giving specific tail allocations the ground time they need at the time they need it.
  FDR – see Flight Duty Regulations.
  FEGP – see Fixed Electrical Ground Point ???
  Ferry flight – A flight leg that has been made necessary in order to make sure that an aircraft is on ground at a given airport at a given time.  It would normally be planned as an empty leg flight with no passenger expected.  However, it may be decided to open this flight up to passengers in order to create revenue from it (compare commercial ferry flight).
  Fictitious point – A location identifier reserved for the purpose of schedule construction to overcome day/date duplication and to describe legs with elapsed times greater than 23 hours 59 minutes.
  FIFO – See First In First Out.
  Finals – (also known as final approach, on finals, c.f. in zone, landed) The stage of an aircraft’s flight between ... (??? of the station at which it is about to land, and actually landing) .  Also a message sent from the ATC (ACARS?) to any systems that need to know the status and ETA of an arriving flight.  Typically this defines a time range between 7?? minutes from landing and having landed.
  First In First Out – A general term used to describe ‘queuing’ operations where the first entity into the queue assumes higher priority than those arriving subsequently.  Thus when dequeuing the entities, the First In becomes the First Out.  Compare LIFO.  In airline planning, “FIFO/LIFO” is used specifically in the context of aircraft rotations where the FIFO heuristic is applied at outstations and LIFO is applied at base stations so as to maximise the time for which aircraft are made available for maintenance.
  FIS – see Flight Information System.
  Fixed Electrical Ground Point – ???
  Fleet – May refer to the complete complement of an airline’s fleet, or a subset defined by: range (e.g. long haul fleet, mid range fleet, short haul fleet); aircraft type (e.g. 747 fleet, A310 fleet); or function (e.g. charter fleet).
  Flight – The operation of one or more legs with the same flight designator.
  Flight attendant –
  Flight designator – A unique identifier for a flight that comprises the airline designator and flight number.
  Flight Duty Regulations – The set of legislation and local agreements that define the working terms and conditions of the cabin and cockpit crews.  This will include things such as maximum working hours, night stop thresholds, breaks and so on.
  Flight Information System –
  Flight interchange – A flight, operated by a single aircraft, of one or more than one leg on which operators differ by leg.
  Flight leg – The operation between a departure station and the next arrival station.
  Flight number – The numerical part of the unique string that identifies each flight.  See flight designator.
  Flying hours – A measure of the accumulated number of hours for which an aircraft has been airborne between specific points in time.  A common use of this is for aircraft maintenance where, for example, there may be a maximum number of flying hours accumulated between maintenance checks.
  Forced connection – (Also known as forced link or forced turn).  This is a constraint imposed by the airline that one flight must be made to connect with another at a particular station.  This is done in order to ensure that  crew or cargo can be transferred between the flights in order to meet commitments.
  Forced link – see forced connection.
  Forced turn - see forced connection.
  Fragile – Applied to a schedule where high flight density, high utilisation of resources, and/or very small amounts of spare time between different flights means that minor delays to one flight cause knock-on and often spiralling delays to other flights.  Compare robust.
  Frequency – (also known as frequency rate) Term used in some airlines in longer term planning where the plan is only concerned with passenger volumes and aircraft types. In this situation a given flight’s frequency may be, say, five times per day.
  Frequential flight – A description of a flight defining it and how it will operate week by week over a given ‘effective date’ range with the same: flight designator, days of operation, and aircraft type.
  Frequential schedule – Sometimes used to describe a schedule whose flights are defined entirely as frequential flights not specific flight instances by date.  Compare [fully] dated schedule.
  Full pax – An aircraft designed or configured to carry just passengers and baggage, not cargo (compare combi).
  Fully dated schedule – see dated schedule.
  Funnel flight – (also known as complexing, starburst, W flight, Y flight).  A flight, composed of two or more members flights, which is identified by the airline designator/flight number of one of the members.  Only one airline designator/flight number is operational on any one leg may have multiple non-operational flight numbers.
  GALILEO – (compare AMADEUS).
  Gate – See departure gate.
  General designator – The unique IATA defined code that identifies an aircraft type.  Also known as General Designator .
  Generic flight –
  Geographic discontinuity –
  GCD – see Great Circle Distance.
  GDS – Global distribution system.
  Gone technical – Applied to an aircraft that has had some sort of mechanical failure that affects its serviceability.
  Grandfather rights – The expectation of an airline to be allowed to continue using a slot that has previously been allocated to them in the past.  Assuming a slot is used for at least 80% of the latest schedule, the same slot would usually be re-allocated without debate when requested for the next season.  If the utilisation falls below this figure, the airline would have to negotiate use of that slot on an equal status with any other airlines that may have requested it.
  Grandfather slot – A specific slot currently allocated to an airline under the assumption of grandfather rights and which on this principle they would reasonably expect to be granted the same slot again for the following season.
  Great Circle Distance –
  Ground time – The minimum amount of time for which an aircraft will need to be on the ground and accessible to ramp staff between arriving from one flight leg and departing on another.  This is decided by two main timings.  One is the ground handling time requirement to enable the aircraft to be cleaned, re-catered, refuelled and so forth.  The other is the technical ground time to allow for maintenance staff to do basic aircraft checks and servicing.  (These are in turn influenced by the aircraft type, station and handling agent performance, and inbound & outbound sectors.)  The ground time is the greater of these two times.
  Ground time exception –
  Handling agent –
  Heavy Maintenance Visit – A major overhaul of an aircraft that is done every few years and requires meticulous logistical planning.  It involves stripping the aircraft down completely and renovating / replacing many parts and fully stripping / repainting the fuselage.  An HMV may take two or three weeks.
  HMV – see Heavy Maintenance Visit.
  Hold - A cargo or baggage carrying compartment of an aircraft.
  Holding area – A region of airport tarmac that is used to temporarily station taxiing aircraft pending, say, a stand becoming free.
  Holding pattern –
  Hub – (Also known as hub station) a … (compare spoke station)
  IATA Airport Handling Manual –
  IATA – International Air Transport Association.
  IATA Code – Unique identifier for an airport.
  IATED – IATA EDIFACT Directory.
  ICAO – International Civil Aviation Organization.
  ICAO Code – A secondary code of four letters used instead of the IATA code to define airports in certain specific contexts: for example NOTAMS.
  ICC – see Interline Communications Committee.
  ICM – see Interline Communications Manual.
  Identifier – A character or group of characters used to identify or name an item of data and possibly to indicate certain properties of that data.
  Interchange – An EDIFACT term for a sequence of EDIFACT messages, of the same or of different types starting with the interchange header and ending with the interchange trailer.
  Interchange header – An EDIFACT term for the service segment starting and uniquely identifying an interchange.
  Intercontinental –
  Interline connection – (also known as interline transfer) The transfer of passengers, baggage, cargo or mail between flights of different airlines.
  Interchange trailer – An EDIFACT term for the service segment ending an interchange.
  Interline transfer – see interline connection.
  IFE – see In Flight Entertainment.
  ILS – see Instrument Landing System.
  In Flight Entertainment –
  In zone – (compare on finals, landed)
  Inertial Navigation System – A navigation device based on detection of tiny changes in acceleration of a known mass on board the aircraft.  By detecting, analysing and integrating these changes, the system can continuously track the aircraft’s displacement in three dimensions, and thus deduce its current position relative to a known starting point.
  INS – see Inertial Navigation System.
  Instrument Landing System – Equipment fitted to an aircraft that allows it to land in conditions of very poor visibility.  These systems fall into different classes according to the minimum visibility in which it enables the aircraft to land.
  Interline – That which occurs between two or more different airlines.
  Interline Communications Committee –
  Interline Communications Manual –  (ATA/IATA).
  Intermediate visit – A particular type of aircraft maintenance check.  See A check.
  International Air Transport Association –
  International Civil Aviation Organization –
  International flight leg – A flight leg between two stations to which different ISO country codes apply.
  Irregularity code – (also known as delay reason) e.g. IR1, IR2...
  ISO – International Organisation for Standardisation.
  ISO country code – see country code.
  ISO 3166 – A standard defining all country codes.
  Intermediate visit –
  Itinerary – A single flight or a series of identical flights defined by a continuous period and days of operation (and frequency rate if applicable), each of which consists of one or more contiguous legs which, taken together, describe the complete routing of that flight.
  IV – see intermediate visit.
  Joint operation flight – A flight on which more than one airline operates one or more of its legs (compare ...).
  Landed –
  Landing –
  Last in First Out –  A general term used to describe ‘stacking’ operations where the latest entity to arrive into a stack sits ‘on top’ of the previous ones.  Thus when unstacking the entities, the latest to have arrived becomes the earliest to leave the stack; and hence the Last In becomes the First Out.  Compare FIFO.  In airline planning, “LIFO/FIFO” is used specifically in the context of aircraft rotations where the LIFO heuristic is applied at base stations and FIFO is applied at outstations so as to maximise the time for which aircraft are made available for maintenance.
  Leased space flight – (also known as blocked space flight) A flight where the operating airline leases (or blocks) some seats/space to one or more other airlines and all participants to such an agreement sell their seats/space on that flight under their own designator.
  Leg – see flight leg.
  Leg Schedule Message – A simple leg-oriented message defined in the  SSIM intended mainly for use in advising ATC authorities and handling agents of schedule information.
  LIFO – see Last In First Out.
  Line of work – (also known as line of duty, compare rotation)
  Line Number – A specific line of duty to be flow comprising flight numbers by aircraft type.
  Local time – The actual time of day at a particular location.  This differs from UTC by a standard variation at any point on the globe.
  Location identifier –
  Long haul –
  LSM – see Leg Schedule Message. 
  Mail – All types of material communications carried on an aircraft, e.g. General Post Office mail, diplomatic mail, and company (airline) mail.
  Main hours – Term used in aircraft maintenance to describe operable hours available
  Maintenance base – An airport at which an airline maintains its aircraft.
  Maintenance  blockings – Also known as a maintenance slot, but not to be confused with an airport slot. A particular time period allocated at a maintenance base during which a particular type of maintenance operation is planned for a specific aircraft type.
  Maintenance checks – see A check.
  Maintenance slot – A particular time period allocated at a maintenance base during which a particular type of maintenance operation is planned for a specific aircraft type (compare slot, see also A, B, C, and D checks).
  Maintenance opportunities –
  Mandatory – The status of a data element or EDIFACT segment composite data element, simple data element, or component data element, marked M, containing information which forms a fundamental part of the procedure and must always be included.
  Market – Often used to describe a particular segment as would be booked by passengers.
  Marketing flight – see duplicate leg (also known as non-operational leg).
  Maximum Take-Off Weight –
  Message – An EDIFACT term for an identified, named and structure set of functionally related data segments as described in a message specification, starting with the message header and ending with the message trailer.
  Message header – An EDIFACT term for the service segment starting and uniquely identifying a message.
  Message trailer – An EDIFACT term for the service segment ending a message.
  Mid fleet – A term sometimes used to describe aircraft that operate over the mid range flight distances.
  MIDT – see …
  Movement – The arrival or departure of an aircraft.
  MTOW – see Maximum Take-Off Weight.
  Narrow-bodied – … (see body type)
  New Generation Large Aircraft – A new style of wide body aircraft currently being designed for operation towards the end of the century.
  NGLA – see New Generation Large Aircraft.
  Night ban – A restriction at a given station giving the latest time at which a flight might be operated.  Such bans are imposed according to different criteria, this differentiates them from curfews.  The most common criteria is the aircraft type, followed by whether the flight is: a specific carrier, charter or scheduled, a ferry flight, or a commercial ferry flight.
  Night stops –
  No-shows – The term for a passenger who is booked on a flight but does not check in to the flight.  Compare show-go.
  Non-co-ordinated airport – An airport that does not have high pressure on its airspace, and as a result can handle flight arrivals and departures without needing to plan and agree slots with the airline in advance.  For such airports, the airlines need only send a Scheduled Movement Advice to notify the expected movement time  (compare co-ordinated airport).
  Non-operational leg – see duplicate leg (also known as non-operational leg, marketing flight).
  NOTAM ­– NOtification To AirMen.  A telexed message sent to notify pilots in particular of special conditions that may apply in certain areas, such as runway restrictions or unusual aircraft operating in the area.
  O&D – see Origin and Destination.
  OAG – see Other Airlines Group.  OAL too???
  OCSC – see Operations Control Sub-Committee.
  Off blocks – ... (also sometimes referred to as off-chocks or chock-off)
  Off chocks – (see/better known as off-blocks or sometimes referred to as chock-off)
  Off pier –   ... service  ... stands (compare On-pier)
  Off point – see Station of disembarkation (compare Board point).
  Offer –
  On blocks – ... (also sometimes referred to as on-chocks or chock-on)
  On chocks – (see/better known as on-blocks or sometimes referred to as chock-on)
  On finals – (compare in zone, landed)
  Online – (also known as on-line) Pertaining to that which takes place within the same airline.
  On-line connection – (also known as online transfer) The transfer of passengers, baggage, cargo, or mail between flights of the same airline.
  On-pier – (compare Off pier)
  Operation – The act of a transport vehicle travelling from point to point.
  Operational reserve – An aircraft that is held in readiness for operation by a carrier but is not normally scheduled into the planned operation and is mainly used to provide additional capacity in the event of unexpected demand, technical failures, resourcing problem, leasing opportunities and so on.
  Operating carrier –
  Operating flight –
  Operational leg – A flight leg which is physically operated and identified by its airline designator/flight number.  Any other airline designators and/or flight numbers associated with the same flight leg are considered to be non-operational flight legs.
  Operations Control Sub-Committee – ...(IATA).
  Operator –
  Origin and Destination – ... (also known as O&D) A flight, or segment of a flight as booked by a passenger that is defined by the city pair at which the passenger(s) initially board and finally disembark.
  Originating flight – A flight designated by a flight designator, commencing at the station in question.
  Other Airlines Group –
  Outstation – An airport to which the airline simply operates but at which it does not maintain aircraft nor out of which it operates crew.
  Overbooking –
  Overbuilt – A term sometimes used to describe an airline’s schedule in the early stages of planning where more flights have been planned than the airline thinks it can resource.  As resource allocations are made, the less profitable flights are dropped from the schedule.
  Overflight – A flight that flies over a given country or region in controlled airspace.  Permission must be gained for overflights by sending a telex request to the authorities of the country being overflown.
  Overhours – Describes an Aircraft that is still in operation even though overdue for a maintenance visit.
  Pairing – British Airways’ term for trip.
  Passenger – Any person carried on and aircraft and covered by a ticket.
  Passenger Reservations Manual – ... (IATA)
  Pattern – see trip.
  PAX – A frequently used short hand for passenger(s).
  Payload –
  Payload exception – Maximum aircraft payloads are defined by the aircraft type but certain geographical regions may need exceptions in this data. Payload exceptions are based on estimated values based on historical trends for both the weight of passengers baggage and the weight of the cargo in the hold. For example, people travelling in Africa carry more baggage than travellers in Europe (i.e. cargo density per region).
  Period ­–
  Plan –
  Planned maintenance –
  PRM – see Passenger Reservations Manual.
  PSC – ATA/IATA joint Passenger Services Conference
  Pushback –
  Qualifier – A data element whose value, extracted from a code list, gives specific meaning to the function of another data element or a segment.
  Ramp –
  Ramp staff –
  Range –
  Reed Travel Group ­–
  Region –
  Registration –
  Reservation – (also known as booking) The allotment in advance of seating or sleeping accomodation for a passenger or of space or weight capacity for baggage, cargo or mail.
  Reservation system –
  Reservations control carrier – The airline which controls the reservations for a flight.
  Return from airborne – When an aircraft has taken off from a station of departure en route to another station, and finds that due to an unforeseen circumstance it has to return to the station of departure (compare Return to stand).
  Return to stand – When an aircraft that has pushed back and taxi’d off stand, but then has to return to a stand due to some unforeseen event without getting airborne (compare Return from airborne)
  Revenue management –
  Robust – Applied to a schedule where low flight density, low utilisation of resources, and/or large amounts of spare time between flight mean that minor delays to one flight do not usually cause knock-on delays to other flights.  Compare fragile.
  Roster – ... typically one month...
  Rotation – Meaning an aircraft rotation.  The operation of consecutive legs with the same aircraft irrespective of the flight designator(s) between visits to (a) maintenance base(s).
  Rotation number – A local term used be some airlines and being an identifier that equates to a virtual aircraft of a given rotation subtype but need not relate to a known aircraft registration.
  Rotation subtype – A local term used be some airlines as a sub-categorisation of standard IATA aircraft subtypes.  A sort of aircraft sub-sub-type.  This is used for aircraft rotations because it ensures that the properties that are important constraints as regards aircraft rotations are preserved regardless of tail assignment.  These properties may be different to those used to categorise subtypes alone.
  Route –
  Routing[s] – A list of consecutive legs in operational sequence between the station of origin and the station of destination of any flight.
  RPL – see ????.
  Saleable seats – The number of seats that can actually be occupied by passengers.  This may be less than the number defined by the aircraft configuration due to having to allow seats for interpreters or long haul crew rests.  This number will also usually be less than the maximum booking levels, as extra bookings are often taken to compensate for a predicted percentage of no-show passengers.
  Schedule – ... (also known as flight schedule).
  Schedule Co-ordination Conference – ... (also known as IATA Conference, Slot Conference)
  Scheduled flight – …(compare charter flight).
  Scheduled Information Request –
  Scheduled Movement Advice – A type of slot notification message that is similar to a Slot Clearance Request except that it does not require confirmation.  It is used at non-co-ordinated airports where the local conditions mean that it is highly unlikely that there will be problems obtaining slots.  The Scheduled Movement Advice simply notifies the airport of an airline’s intention to operate that slot, and the airline will assume that the slot will be available unless they are told otherwise.
  Scheduled Time of Arrival –
  Scheduled Time of Departure –
  SCC ­– see Schedule Co-ordination Conference.
  SCR – see Slot Clearance Request.
  Season –
  Season code –
  Sector – A city pair that will be flown via a single flight leg.
  Segment [1] – The operation between board point and subsequent off point within the same flight.
  Segment [2] – An EDIFACT term for ...
  Segment terminator – ...
  Segment character – ...
  Service segment – see segment.
  Service type –
  Shared airline designator flight – A flight designated by a flight designator of one airline but operated by another airline on its behalf as part of a commercial agreement.
  Short connection – A connection where the departing flight leaves earlier than the minimum planned connection time should allow, resulting in either rushed passengers or even missed connections.
  Short haul –
  Show-go – The term for a passenger who has checked in and has baggage in the hold but shows up at the checkin gate at the last minute – or even late – knowing that the aircraft is unlikely to depart without him as his baggage would have to be removed from the hold first.
  SI – see Supplementary Information.
  Simple data element – An EDIFACT term for a data element containing a single value.
  SIR – see Scheduled Information Request.
  ------------------------------------------------ Still to rationalise from here on. --------------------------------
  SISC – Schedules Information Standards Committee (IATA)
  SITA – Société Internationale de Télecommunications Aéronautiques.
  SKM – (SKm) see Available Seat Kilometres.
  Slot – The scheduled time of arrival or departure available or allocated to an aircraft movement on a specific date at a specific airport.  Although this, the official IATA definition of a slot, is purely to do with a given date/time at a given station; the practice is sometimes different.  If, for example, a slot has been confirmed but the aircraft type is subsequently changed, this should make no difference.  However, if the airport’s resources are already at their limit, and the change is, say from narrow body to wide body, the airport may decide it simply can’t cope and refuse the slot/change.  In practice then, a slot is really a combination of both a particular time window and implied resource/throughput demands a the station in question.  Compare maintenance blocking.
  Slot Clearance Request
  SMA – see Scheduled Movement Advice.
  SPC – Scheduling Procedures Committee (IATA)
  Spoke station –
  SSI message – A loose term used to describe any of the standard schedule messages defined in the SSIM.
  SSIM – Standard Schedules Information Manual published twice yearly by IATA
  SSM – (c.f. ASM) Standard Schedules Message
  STA – see Scheduled Time of Arrival.
  Stand –
  Stand allocation –
  Standard variation – The number of hours (or hours-and-a-half) by which a particular station is ahead of or behind UTC, or the difference in time between a time zone’s local time and UTC.  This may also be applied during periods of Daylight Saving Time in which case the standard variation will be different (normally by one hour) to the standard variation during normal local time.
  Starburst– see funnel flight (also known as, complexing, W flight, Y flight)
  Station – A place to which a location identifier has been assigned.
  Station of destination –
  Station of embarkation – The station at which passengers board the aircraft (also known as board point).
  Station of final destination (also known as station of ultimate destination)
  Station of origin
  STD – see Scheduled Time of Departure.
  Stopover – (also known as break of journey) A deliberate interruption of a through journey by the passenger at a station between the station of origin and the station of ultimate destination.
  Subseason – Any period of time greater that one day that falls wholly within a given season.
  Sub-type Code – (see Aircraft Subtype)
  Summer season
  Supplementary Information – A line in an SCR telex that introduces a pain language remark in free format text.
  Swap –
  Tail number – see aircraft registration.
  Tail assignment – The process of deciding which specific aircraft (identified by their aircraft registrations) are to be allocated to particular uses (e.g. rotations, flights, stand allocations etc.).
  Taxi –
  Taxiway –
  Technical landing – A landing for non-traffic purposes.
  Terminating flight – A flight, designated by a flight designator, ending at the station in question.
  Tie – Used in schedule planning (particularly when doing aircraft rotations) to mean the situation where two or more aircraft either arrive at or depart from a station at the same time.
  Time zone – A geographical area internationally recognised as operating to the same local time throughout that zone.  One time zone will operate at a different local time to all others.  This difference is in whole or half hour intervals.  The time zone is defined as having a certain number of hours or half hours difference from UTC.
  Timetable
  TKM – (or TKm) see Available Ton Kilometres
  Tow, Towing ­– Aircraft being moved within an airport by special tug vehicles rather than under their own power.
  Tower hours –
  Traffic restriction – A limitation on flights that may operate over specific sectors.  This may be due to equipment restrictions (e.g. aircraft without dingys not allowed to fly over water) political problems (flights from unfriendly countries not allowed in) and so on.  The format of a traffic restriction notice is defined in the SSIM, but the semantics of the message are not prescribed by IATA.
  Traffic rights – The right to fly specific types of flight over a country (c.f. overflight).
  Transfer – see connection.
  Transit flight – A flight, designated by a flight designator, during an en route landing at the station in question.
  Transit station/airport – A scheduled en route stopping station on a flight.
  Transit time – The time an aircraft remains in transit at the station in question, i.e. from the time the aircraft is on blocks to the time it is off blocks at a station where it is not being turned round, but is simply continuing on another leg of the same flight (compare turnaround time, crew turnaround time).
  Trip –  A work package consisting of an anonymous crew roster and a number of duties.  Each duty may include zero or more flight sectors and/or other activities.  A trip commonly consists of several flights originating from and returning to a home base, and a full complement of crew roles for those flights.
  Turnaround – The station in an aircraft rotation, where the flight number changes.
  Turnaround Time – The time an aircraft spends at a station when it is not considered to be operating a flight (i.e. from the time the aircraft is on blocks to the time it is off blocks) and where it is doing a turnaround (compare transit time).
  Typical week – A way of defining a period of a schedule by assuming that the flights in a given (typical) week will exactly repeat each week over that period.  Note that ‘BLUESKY’ will provide fully dated schedule operations not typical week ones.
  UN/ECE – United Nations Economic Commission for Europe.
  Unit load device – A load carrying device which interfaces directly with aircraft loading and restraint systems and meets all restraint requirements without the use of supplementary equipment.  As such it becomes a component part of the aircraft.  The device can be either a combination of components or one complete structural unit.  A combination unit is an aircraft pallet plus net plus non-structural igloo, or pallet plus net.  A structural unit is a lower deck or a main deck cargo container, or a structural igloo assembly.
  UTC – Universal Time Co-ordinated.  A single time reference point being the agreed time at zero degrees longitude without correction for daylight saving time (see also standard variation, local time).
  V171 –
  Variant –
  Virtual segment –
  W check – see A check….
  W flight – see funnel flight (also known as, starburst, complexing, Y flight)
  Waitlisted slots – When a slot is being negotiated, the slot request may be rejected but the requester still asks to be put on a reserve list for the slot in the event that it becomes free later.  These slots are know as the requestester’s waitlisted slots.
  Wet lease – An aircraft leasing arrangement where the lessor provides the aircraft in a ready-to-fly state including crew (compare dry lease).
  Wide-bodied – … (see body type).
  Winter season
  Y flight– see funnel flight (also known as, starburst, W flight, Complexing)
  Yield –
  Yield management – Any process of maximising revenue by tuning what the airline offers the passenger so as to increase the revenue accrued for a given flight.  This may not equate to maximising seat occupancy as, for example, it may be more profitable to cut-off the number of cheap advanced bookings in the expectation of getting (possibly fewer) late bookings at a much higher fare.
  Zero Fuel Weight – The weight of an aircraft with no fuel on board.
  ZFW – see Zero Fuel Weight