Why airport codes don't match their cities: ORD, LAX, YYZ and more

How airport codes are chosen

The three letters on your boarding pass and bag tag are an IATA location code. IATA, the airlines' trade association, hands them out under its Resolution 763, and only when an airline asks: usually the first airline to fly to a new airport. The rule is simple. The first choice is the first three letters of the place's name. If those are taken, the next choice is a free combination, preferably starting with the place's first letter. Every code must be unique, and with about 11,300 of some 17,000 possible combinations already in use, the obvious letters are often gone.

Codes also have to last. IATA treats them as permanent and changes one only for a strong reason, usually safety. So when an airport is renamed, or its city is, the code stays as it was.

That leaves three kinds of codes that don't match their city: codes from an old name, codes that had to avoid letters already taken or set aside, and codes from somewhere other than the city itself.

Codes named after the airport's old name

Many of the best-known mismatches spell a name the airport no longer has.

Chicago chose Orchard Field for its new airport in 1945 and renamed it in 1949 after Edward "Butch" O'Hare, a naval aviator. New Orleans began commercial flights at Moisant Field, named after the aviator John Moisant, in 1946. Orlando's code comes from McCoy Air Force Base, which closed in 1974; the airport became Orlando International in 1976. In each case the airport changed its name and kept its letters.

Whole cities have been renamed under their codes too. Mumbai is still BOM, Chennai MAA and Kolkata CCU: the letters of Bombay, Madras and Calcutta. Beijing is PEK, from Peking; Ho Chi Minh City is SGN, from Saigon; and St Petersburg is LED, from Leningrad.

The X in LAX

In the 1930s airlines chose their own two-letter codes, and Los Angeles was simply LA. By the late 1940s there were too many airports for two letters, and the codes grew to three; Los Angeles became LAX in 1947. The X means nothing: it filled the third place. Newspaper histories say Portland's PDX and Phoenix's PHX gained their X the same way. IATA took over the codes from the airlines in the 1960s.

Letters that were already taken

In the US, some first letters were set aside before the airlines got to them. The FAA, which gives US airports their identifiers, does not hand out three-letter ones that start with N, W, Y or Z. N is the US Navy's. K and W begin the call signs the FCC gives radio and television stations, Q belongs to international telecommunications, and Z marks the FAA's own air route traffic control centres.

Most big US airports use the same three letters for the FAA and for IATA, so a US airport code starting with N or W is rare. Newark is EWR, and Norfolk is ORF.

Canada's Y

Almost every big Canadian airport starts with Y: Toronto Pearson is YYZ, Montreal YUL, Vancouver YVR and Calgary YYC. IATA dates the habit to before the Second World War and says it is believed to come from the two-letter codes of weather stations or radio beacons. It also says new Canadian codes no longer have to follow it.

Why Toronto is YYZ in particular has no official explanation. The stories online, most of them about an old weather station at Malton, where the airport stands, are just that: stories nobody has been able to confirm.

Codes from somewhere else

Some codes match a place, just not the city on the ticket.

• CVG, Cincinnati. The airport is in Boone County, Kentucky, across the Ohio River. Its code comes from Covington, the Kentucky city across the river from Cincinnati, because CIN was already taken.
• IAD, Washington Dulles. It was first coded DIA, and IATA changed it to IAD because DIA was too easily confused with DCA, Washington's other airport. It is IATA's own example of a code that had to change.
• WAS, Washington. Cities with more than one airport can have a code of their own: WAS covers DCA, IAD and BWI. A city with one airport shares its code, like Geneva's GVA.

IATA codes and ICAO codes: JFK and KJFK

Pilots and air traffic controllers use a different code: ICAO's four letters. ICAO, the UN's aviation agency, publishes them for airports commercial or not, for flight plans and air traffic control. The first letter is usually the region and the second the country: Barcelona's LEBL is L for southern Europe and E for Spain. Canadian airports start with C, as in CYYZ.

In the contiguous US, the ICAO code is a K in front of the airport's FAA identifier, so New York's JFK is KJFK and Chicago's ORD is KORD. Alaska and Hawaii have their own prefixes: Honolulu is PHNL.

The big letters on our prints are the IATA code, the one on the bag tag. Under them sits the city, and under that the date: how a day of real flights becomes the print above them.