Airport codes—we see those three letters every time we book a flight or check in our luggage. Some of you even refer to your own airports with those three letters. How many people do you hear saying JFK instead of John F. Kennedy International Airport, or SFO instead of San Francisco International Airport? Probably very few.

But do you know how an airport gets a code assigned? Or, that those codes are actually four letters long? When it all comes down to it, there’s a lot that goes into naming and assigning then you may think.

The History

Airlines began to assign codes to airports in the 1930s, which consisted of two letters. In the 1940s, the number of airports grew, creating a need for a new coding system. As such, the three letter code came to life—the same ones we know today.

In the 1960s, airlines decided they needed a formal process in order to avoid any confusion between airports. As such, two organizations were given the task of assigning codes to airports. One is the International Civil Aviation Organization (ICAO), a branch of the United Nations that overseas aviation regulations, and the other is The International Air Transport Association (IATA), a trade organization for airlines.

ICAO assigns four letter codes utilized by airlines in mapping out their flight plans, as well as by air traffic control. The first letter in the code is associated with the country, whereas the other three letters indicate the airport. For instance, LAX is KLAX—the “K” stands for “U.S.”, and LAX is the particular airport.

The IATA assigns the more commonly known three letter code for every airport—IAH (Houston), SVO (Moscow), LIS (Lisbon). At times, the code IATA is the same as the last three letters that the ICAO assigns, but this doesn’t always happen.

The Assignment

How do codes get assigned? First, it’s important that the airport code is unique—no two airports have the same code. Second, the criteria used to assign a letter is based on the city the airport is located in, or if there are two airports in the same city, the other one may be assigned a code pertaining to a key descriptor. One example is Louis Armstrong New Orleans International Airport, which has been assigned MSY as its airport code. It originally stood for John Moisant, a famous pilot who crashed where the airport was later built. Other airports have been assigned more interesting and funny codes such as LOL (Derby Field airport in Nevada), OMG (Omega Airport in Namibia), BAD (Barksdale Air Force Base in Louisiana), and SUX (Gateway Airport in Iowa).

What’s your favorite airport code?