How Are Airport Codes Determined?

Airport codes are a shortcut to identifying airports without needing to write out the full name of the facility. Whether it’s on checked baggage tags, boarding passes, or that inflight tracker, you’ll find airport codes at several places along your journey. Some of these three-letter codes make sense and correspond easily to the city you’re flying to. Others not at all. So how are they determined?

Los Angeles International Airport has the IATA code of LAX. Photo: Getty Images


Before we begin, it should be noted that there are actually two sets of codes for airports: IATA (International Air Transportation Association) and ICAO (International Civil Aviation Organization).

  • IATA three-letter codes are used for passenger-facing operations: As previously mentioned, this might be boarding passes, baggage tags, some airport signage.
  • ICAO codes, also known as “location indicators,” consist of four letters and are used within the industry- think pilots, air traffic control, airline operations planners, etc.

Determining IATA codes

In short, determining which three letters make up an IATA travel code comes down to two main things:

  1. How the airport wishes to identify itself
  2. The availability of that letter combination (to ensure there are no duplicates)

However, when it comes to the first reason, this can be for a wide array of factors, which include:

Closely matching the city or region that the airport serves:

  • Amsterdam (AMS)
  • Madrid (MAD)
  • Mexico City (MEX)
An old airport sign showing some of the world’s airport codes. Photo:

One good example of the ‘fluid’ nature of IATA codes was with “IST”: Only a few years ago, Istanbul Atatürk Airport was the main facility serving the city of Istanbul, Turkey. Sabiha Gökçen Airport also served the city, but to a lesser extent.

As such, the Atatürk Airport designated itself as IST for Istanbul. However, it was decided that the shiny, new main international facility, “Istanbul International Airport,” should have the code IST. Thus, Atatürk Airport then became ISL instead.

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Airports might also use letters that correspond with the name of the airport (sometimes this is a name that honors a historical figure):

Then there are other reasons that have an assortment of historical origins. For example, the airport that serves the city of Bishkek, Kyrgyzstan, has the IATA code of FRU. This originates from the Soviet name of the city of Bishkek, then called Frunze.

Canadian airports (in general) all begin with the letter Y. This has a history and explanation all its own, which can be found in a previous article.

Most Canadian IATA airport codes begin with the letter Y. Photo: Daniel via Wikimedia Commons 

Determining ICAO codes

ICAO’s four-letter location indicators range from being “a little different” from the corresponding IATA code, to not at all the same. When it comes to being very similar, this typically involves having the additional letter first, which indicates the region of the aerodrome. Here are some examples:

  • All continental US airports begin with the letter K: KLAX, KJFK, KORD – these correspond with LAX, JFK, and ORD, respectively.
  • Canadian airports begin with C: CYVR, CYYZ, CYUL, corresponding to their IATA codes of YVR, YYZ, and YUL, respectively.

As you can see in these cases, the IATA code is simply the ICAO code minus the first letter.

The regions and their ‘first letters’ as designated by ICAO. Photo: Hytar via Wikimedia Commons 

And then, there are ICAO codes that have no resemblance to their IATA counterpart. This is due to ICAO’s system. While the first letter will strictly represent the region, the second letter generally represents a country within that region.

  • EGLL represents London Heathrow (IATA: LHR), with G designating it a UK airport.
  • EYVI represents Vilnius airport in Lithuania (IATA: VNO). It is in the same region as London Heathrow and thus starts with E. The second letter, Y, indicates that it is in Lithuania.

To summarize, four-letter ICAO codes have a more rigid structure, with the first two letters being tied to an airport’s geography. IATA codes, on the other hand, do not have such rules. While they will often correspond to the city an airport serves, there are many more reasons for assigning codes and will depend on each and every airport.

Did you know about the reasons behind selecting airport codes? Let us know in the comments.