3. Location Identifier Systems
While many countries and other aeronautical agencies have in the past devised systems of identifiers for airports, airfields and other aviation-related facilities, there are four main systems in use today, two of them worldwide in scope and the other two specific to the USA and Canada.
All four systems have the same aim - to provide an unambiguous means of referring to specific airports. However there are a number of important differences between the rules adopted by each of the systems.
Each is considered in turn below.
4. IATA - International Air Transport AssociationIATA
’s stated mission is "to represent and serve the airline industry", and so its focus is on commercial air transport. Originally founded in 1919, it now groups together nearly 270 airlines which between them fly over 95 percent of all international scheduled air traffic.
IATA Resolution 763 states that all member airlines and CRSs shall use the location IDs published three times per year in the "Airline Coding Directory"; principal applications are for ticketing, reservations and baggage handling, together with numerous other uses.
Location IDs covering airports in the United States are assigned by IATA in conjunction with the Air Transport Association (ATA) - the trade organisation for the principal US airlines.
Main features of the IATA/ATA location identifier system are:
- All codes are combinations of three letters (e.g., JFK)
- Approximately 50 combinations are reserved, and not available for assignment to airports (e.g., HDQ, QZX, ZZZ, etc)
- Wherever possible, IATA assigns codes which coincide with the first three letters of the location name (e.g., BOGota, SINgapore, SYDney) or at least with the first letter of the name. Codes may also correspond to less obvious historical associations for a location (e.g., ORD, MCO). In other cases, the first letter of an airport’s name is omitted and subsequent letters used (e.g., cORK, wILMington)
- Codes may also be assigned to non-airport locations such as rail and bus stations and other "off-line points" (such codes normally start with Q, X or Z)
- Codes are considered permanent, and are rarely reused; a standard exception to this is when a new airport such as Denver or Munich is constructed to replace a city’s current airport, and the existing code for the previous airport is transferred
- Codes for US airports are normally (but not always) the same as the FAA-assigned three-letter codes for the same location (see below for examples of exceptions).
- Codes for Canadian airports are normally (but not always) the same as the Transport Canada-assigned three-letter codes for the same location (see below for examples of exceptions).
- By convention, heliports are often assigned codes starting with J, though this is not mandatory
- A location may, in rare cases, have more than one code assigned to it simultaneously.
- The IATA resolution also makes reference to "metropolitan areas", which can also be allocated codes in the same sequence. The resolution offers no definition of these, although it can be inferred from the Airline Coding Directory that a metropolitan area contains two or more locations, each of which has an assigned IATA code. It is unclear as to whether these locations must both be airports or whether a metropolitan area may contain, for example, an airport and a bus or rail station. On one hand the resolution refers to "… a request to remove an airport from a metropolitan area comprising only two airports and the consequential dismantling of that metropolitan area" - which implies that a metropolitan area must consist of two or more airports. However there are many examples in the Airline Coding Directory of metropolitan areas comprising a single airport plus one or more non-airport locations (e.g., BHX, BTS, BUF).
- The resolution also says that if a metropolitan area is served by only one airport, the same code is used for the area and the airport; if an area is served by more than one airport, each airport will have its own code, and the code for the metropolitan area will be either one of the airport codes, or a unique code of its own. It follows that if a location "belongs" to a metropolitan area with a different code (eg ORD/CHI) then there must be other locations belonging to that area (in this case MDW, PWK, etc.).
- For many applications, it is convenient to consider every location as belonging nominally to its own metropolitan area (ie each location will have both a location code and a "city" code).