The first time I flew through Chicago O'Hare, I stared at my boarding pass and thought it had to be a typo. ORD? For O'Hare? I spent the whole layover Googling it, and fell into a rabbit hole that ended with a Sioux City gift shop selling "Fly SUX" merchandise. Airport codes are assigned by a real system, but the system is layered on top of 80 years of history, military airfields, renamed cities, and codes that were simply already taken.
Who does the assigning
The 3-letter codes on your ticket are assigned centrally by the International Air Transport Association (IATA). The core rules are simple: the code must be unique, and it usually derives from something recognizable. In practice, "recognizable" covers a lot of ground, because the obvious letters are often taken by somebody else.
That is the key to the whole mystery. Dubai could not be DUB, because Dublin got there first. New Orleans could not be NOL; the code belonged to an airport on Poland's Nakolik River. When the obvious choice is taken, IATA reaches for the airport's name, its former name, or, in rare cases, just letters that were available.
The usual patterns
Most codes fall into a few buckets. City-name codes are the friendly ones: MIA for Miami, ATH for Athens, LAX for Los Angeles. Airport-name codes show up where a city has several airports or the airport itself is famous: JFK for New York's John F. Kennedy, LHR for London Heathrow, CDG for Paris Charles de Gaulle, BWI for Baltimore/Washington International. Multi-city airports mash names together: DFW for Dallas/Fort Worth, MSP for Minneapolis-Saint Paul, RDU for Raleigh-Durham.
My favorite category: the ghost names
This is where it gets fun. A huge number of confusing codes are fossils, left over from what the airport used to be called:
| Code | Airport | The ghost name |
|---|---|---|
| ORD | Chicago O'Hare | Orchard Field, the site's name before 1949 |
| MCO | Orlando International | McCoy Air Force Base |
| MSY | New Orleans | Moisant Stock Yards, near the old Moisant Field |
| FAT | Fresno Yosemite | Fresno Air Terminal |
| LCK | Rickenbacker (Columbus) | Lockbourne Air Force Base |
| CMH | John Glenn Columbus | Columbus Municipal Hangar |
| IAD | Washington Dulles | International Airport Dulles |
| DCA | Reagan National | District of Columbia Airport |
Chicago's story is my favorite. The site was a Douglas aircraft plant next to a farming community called Orchard Place. The airfield became Orchard Field, got the code ORD, and then in 1949 the city renamed it for Edward "Butch" O'Hare, a WWII flying ace and Medal of Honor recipient. The name changed; the code stayed. Eighty years later, millions of travelers a year type ORD without knowing they are typing the name of an apple-growing settlement.
The ones that just make you laugh
Some codes are accidents that stuck. Sioux City, Iowa, is SUX, and after years of trying to get it changed, the airport gave up and started selling "Fly SUX" souvenirs, which I respect enormously. St. Pete-Clearwater is PIE. Derby Field in Nevada, serving Lovelock, is LOL. Kahului Airport in Hawaii is OGG, named for local aviation pioneer Jimmy Hogg, which is a much better story than a joke.
Old city names survive too. Beijing's main airport is still PEK, from when the city was romanized as Peking. Mumbai kept BOM from Bombay, Chennai kept MAA from Madras, and St. Petersburg is LED from Leningrad. Renaming a city does not rename its code, and in my opinion that is exactly right: codes are infrastructure, and infrastructure should not wobble every time a map gets redrawn.
Can a code change?
Rarely, but yes. Codes are deliberately stable because they are embedded in ticketing systems, baggage networks, and navigation databases worldwide. When they do change it is usually geopolitics, like Berlin Schonefeld keeping SXF but changing its ICAO code after German reunification. For IATA codes, the bias is overwhelmingly toward keeping the old one, ghosts and all.
Look up any US code
Now that you know the stories, you can check the codes yourself:
Search the free US airport codes database
It covers 679 US airports with scheduled airline service, with IATA and ICAO codes, city, and state, plus a free CSV download. Data comes from OurAirports and is released to the public domain.
Sources: Wikipedia, "IATA airport code"; Fodor's, "How Do Airports Get Their Codes"; Aviation Week, "The Mystery of Airport Codes"; Travel Tomorrow, "Ever wondered how airport codes are assigned?" Verified October 2026.