If you’ve ever traveled, you’ve undoubtedly seen them everywhere—on tickets, baggage tags and departure and arrival displays: three-letter airport codes. Some, like BOS or LAX, are instantly identifiable. Others (here’s looking at you, OGG) seem more like cryptic puzzles waiting to be decoded.

So who decides what those letters representing airports should be, and how do they come up with these designations? Reader’s Digest went right to the source—the Montreal-based International Air Transport Association (IATA), which represents hundreds of airlines—to get the scoop.

Read on to discover the surprisingly in-depth mix of history, happenstance and sometimes head-scratching logic behind those seemingly simple airport identifier codes.

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What’s the history of airport codes?

Those airport codes didn’t start out as three letters. Here’s a little airplane trivia for you: In the 1930s, airlines began using two-letter airport codes, according to the IATA, and they were often based on the National Weather Service’s designations. The practice worked fine for a time, but by the late 1940s, aviation had taken off so much that airports outnumbered the available two-letter codes (676, for those keeping count). As a result, the system was forced to expand to three-letter codes, opening up a more accommodating 17,576 options. The triple-letter system is still the standard today.

Take Los Angeles International Airport, for example: In 1947, it switched from LA to LAX (the extra X was a popular, generic placeholder at the time). By the 1960s, commercial airlines asked the IATA to be responsible for standardizing these airport codes for consistency, and the organization has been assigning them ever since.

What’s the procedure for IATA assigning codes?

Requesting a new airport code isn’t a free-for-all—it follows a well-defined process. “The rules for the assignment of location identifiers are straightforward and are laid down in IATA Industry Resolutions, which have been developed in conjunction with IATA Member Airlines,” says the IATA coding team.

When aviation officials apply for an IATA code, they typically propose a three-letter combination that best reflects the location (think: DEN for Denver, or BOI for Boise). They must check a master coding directory to make sure that another airport doesn’t already use the one they’re requesting, and they submit a second, just-in-case choice, ideally starting with the airport location’s same first letter.

Can airports change their codes once assigned?

The short answer: rarely. “According to the applicable IATA Resolution, IATA Location codes are assigned permanently with very few exceptions—for example, when a change is needed to address air safety,” the coding team says. For instance, two airports with similar codes in the same region could result in confusion and navigational errors.

Nevertheless, changes have happened on rare occasions. New York City’s Idlewild Airport once used IDL, but it was renamed in honor of John F. Kennedy following his assassination. “It took a lot of political pressure for the FAA to relax its rule about the unchangeability of codes and assign the letters JFK, but this was eventually approved,” the IATA says. Fun fact: IDL was reassigned to Indianola, Mississippi.

What’s the backstory on some of the less intuitive airport codes?

Man checking his flight on the timetable display at the airportDAVID-PRADO/GETTY IMAGES

Not every code is as obvious as BOS for Boston. Orlando International in Florida, for instance, goes by MCO—a throwback to its former identity as McCoy Air Force Base. Westchester County Airport near White Plains in New York goes by HPN, which some say reflects neighboring towns Harrison, Purchase and North Castle.

Then there’s OGG, or Kahului Airport in Maui, named for Hawaiian Airlines Chief Pilot Jim Hogg. He reportedly chose OGG over the more literal—but unintentionally cheeky—option of HOG, which now belongs to Frank Pais International Airport in Holguin, Cuba.

What are some of the funnier airport codes?

With thousands of three-letter combinations in circulation, it’s almost inevitable that some will have humorous double meanings. Here are a few of the best—or at least the most eyebrow-raising:

  • Derby Field outside of Lovelock, Nevada, goes by LOL.
  • Sioux Gateway Airport in Sioux City, Iowa? That would be SUX.
  • Omega Airport in Namibia has the playful OMG.
  • BUM belongs to Butler Memorial Airport in Missouri.
  • And POO serves Poços de Caldas, Brazil.

Are IATA codes only used for airports?

Surprisingly, no. While the IATA may be best known for airport codes, it also assigns identifiers to non-airport locations like rail and bus stations. Why? The coding team explains, “This is at the request of an airline who wishes to establish one ticketed journey for passengers, [since] intermodal journeys are becoming more and more popular.”

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Aaron Rasmussen
Aaron is an accomplished travel and lifestyle writer with decades of experience across digital and print publications. His adventures through more than 50 countries have included navigating Iceland’s Ring Road, traversing Peru by luxury train, yachting in the Seychelles, and eating and drinking his way through Italy. His work has been featured in...
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Aaron Rasmussen