They are on every airline reservation, baggage tag and boarding pass you have ever received, those 3 little capitalised letters. But what do they mean and where do they come from?

IATA codes differ from ICAO (International Civiil Aviation Orgainisation) codes. These  are made up of 4 letters instead (456976 combinations!) and are used for all aerodromes around the world not just ones that allow for commercial aircrafts. They are used to identify other aviation facilities such as weather stations, flight service stations and area control centres whether they are located at airports or not.

Lets go back to the start. When the Wright brothers first took the skies in 1903 airports did not exist but as air travel became more common there was a need for categorising the increasing number of destinations that could be flown. Initially pilots in the United States used the two-letter code from the National Weather Service (NWS) for identifying cities. This system became unmanageable for cities and towns without an NWS identifier, thus a three-letter system of airport codes was implemented, today being designated by IATA (International Air Transport Authority).

To ease the transition many existing airports simply placed an X after the weather station code, hence LA became LAX, Portland became PDX and Phoenix PHX etc. Incidentally at the historic sand dune in Kitty Hawk where the first flight occurred the U.S. National Parks Service maintains a tiny airstrip called FFA — First Flight Airport.

Many stations are simple and obvious using the first 3 letters of  their city name, for example MADrid, SYDNEY, MIAmi. Others use the first letters of their city name, Salt Lake City (SLC) and Port of Spain. Others are based on the area of the city they are based, for example the Buenos Aires suburb of EZEiza, OToPeni, the suburb of Bucharest, Rio De Janeiro’s  Galeao (GIG) and Rome’s Fiumicino (FCO). London having so many airports is forced to use the smaller towns  they are based to avoid confusion whilst retaining its heady global city title (London Heathrow (LHR), London Gatwick (LGW) and London City (LCY).

History, rather than geography, solves the puzzle of TYS, GEG, OGG and MCO. Knoxville, also in Tennessee, doesn’t have a single letter in common with its tag of TYS; however, a historian would know that the TYSon family donated the land in honor of their son killed in World War I. The current Orlando International Airport stands on the land that used to be McCOy Air Force Base  Spokane International Airport is coded as GEG in honor of Major Harold C. Geiger, a pioneer in Army aviation and ballooning. Geiger field was renamed in 1960 but the code was not changed. Kahului Airport, Maui, was designated as OGG in honor of aviation legend, and Lihue native, Hawaiian Airlines Capt. Bertram James ‘Jimmy’ HOGG

One of the world’s largest airports, JFK, is also one of the very few that changed call letters. A change is rare because an identifier becomes so well known to airline staff that changes are not normally permitted. Interestingly the John F. Kennedy airport’s former code also came from the name of the field — IDL for Idlewild airport (itself named for the Idlewild golf course whose land became JFK).

Many IATA airport codes point to their previous ‘colonial’ name. BOM (Bombay (Mumbai), SGN (Saigon/Ho Chi Minh City), PEK (Peking/Beijing), LED (Leningrad / St. Petersberg).

What of cities of the same name? Where would us travel agents be without airport codes to distinguish the many common Latin city names such as Santa Maria, Santiago and San Salvador. Flying people to the wrong country most likely! In the same vein when Dubai Airport was built and they saw the obvious choice of DUB already taken by Dublin they sensibly added an X in the middle  (DXB) to make it clear we couldnt book the fair skinned Irish to frazzle in the desert.

Further to avoid confusion in the United States they state that the first and second letters or second and third letters of an identifier may not be duplicated with less than 200 nautical miles separation. District Of Columbia Airport meant that the nearby and newer Dulles International Airport had to re-jig its initial to form the current IAD, rather than the more obvious choice of DIA.  Houston’s new Intercontinental Airport (IAH) had to adopt something much different than the older HOU (Hobby Airport) across the city.

If you have ever laid awake wondering why no United States airports begin with the letter N wonder no more. It is because these have been specially reserved for the US Navy bases, NPA (Pensacola) and NKX (Miramar, California) are where the nations best pilots learn their trade. Whereas the Federal Communications Commission has taken all the ‘W’ and ‘K’ codes. Cities that begin with these have had to make up irregular airport codes, hence EWR for Newark, EYW for Key West and ILM (Wilmington) Internationally you will not find any commercial airport codes beginning with Q, as this was reserved for international communications, cities beginning with ‘Q’ had to find alternate codes.

And what about those pesky Canadian airport codes, that all begin with Y, the bane of the travel agents and check-in staff’s lives. Four of the ten provincial capital airports in Canada have ended up with codes beginning with YY, including YYZ for Toronto, Ontario, YYJ for Victoria, British Columbia, YYT for St. John’s, Newfoundland, and YYG for Charlottetown, Prince Edward Island. Canada’s largest airport is YYZ for Toronto-Pearson. When the Canadian transcontinental railways were built, each station was assigned its own two letter Morse code. VR was Vancouver, TZ Toronto, QB Quebec, WG Winnipeg, SJ St. Johns, YC Calgary, OW Ottawa, EG Edmonton, etc. When the Canadian government established airports, it used the existing railway codes for them as well. If the airport had a weather station, authorities added a “Y” to the front of the code, meaning “Yes” to indicate it had a weather station.

There are other fun ones. FAT is Fresno, California. DUM is in DUMai, Indonesia, whie Norway’s Bodo Airport is BOO. Harbour, Eolie Island, in Italy is ZIP. Headingly, Australia, is HIP. Hot Springs, Arkansas, is HOT. And Willow, Alaska, is WOW. Also I couldn’t do this article without adding in some some rude ones such as COK (Cochin, India), FUK (Fukuoka, Japan), NOB (Nosara, Costa Rica) and DIK (Dickinson, USA).

With 17576 3-letter combinations available and air travel becoming more common is there a chance we could run out of airport codes? Well this is very unlikely. As it is there are ‘only’ 9000 commercially registered airports so that leaves plenty of space left and plenty more codes to make up in the future.