Airline and airport code system: How are they determined?

Photo: Pxhere

An IATA airport code, also known as an IATA location identifier, IATA station code, or simply a location identifier, is a three-letter geocode designating many airports and metropolitan areas around the world, defined by the International Air Transport Association.

Airport codes are divided into two types: IATA codes (three letters) for passenger operations and ICAO codes (four letters) for industry use.

IATA

IATA codes are determined based on how the airport wants to identify itself and the availability of the letter combination.

IATA three-letter codes are used for passenger-facing operations: This is what most passengers will be familiar with, and the codes used on tickets, boarding passes, and signage.

In short, deciding which three letters make up an IATA travel code comes down to two main things: How the airport wishes to identify itself and the availability of that letter combination to ensure there are no duplicates.

However, the first reason can be due to a multitude of factors, which include matching the city or region an airport serves. For example, Amsterdam Schiphol International Airport (AMS), Adolfo Suárez Madrid-Barajas International Airport (MAD), Mexico City International Airport (MEX)

Only a few years ago, Istanbul Atatürk Airport was the main facility serving the city of Istanbul, Turkey, and held the IST code. However, when the new Istanbul International Airport opened in 2018, the IST code was transferred over, with Atatürk being assigned ISL instead.

Many countries use their airports and codes to honor leaders or other historical figures. Some famous examples include:

JFK: New York's biggest airport is named after the 35th US President, John F. Kennedy, who was assassinated in 1963.

CDG: Paris' main airport is named after Charles de Gaulle, the military leader who went on to become the first president of the French Fifth Republic.

BOM: Mumbai was named Bombay during the British reign in India, and since the first airport opened during that time, it adopted BOM as its code, one it holds today as well.

ICAO 

ICAO codes can differ from their corresponding IATA codes and follow a more rigid structure based on an airport's geography and region.

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.

ICAO's four-letter location indicators range from being slightly different from the corresponding IATA code to not at all the same.

Regarding those that are relatively similar, this typically involves having the additional letter first, which indicates the region of the aerodrome.

For example, 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, and 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. However, since one region can have multiple countries, and only North America has its own breakdowns, it's a bit more complicated.

Some ICAO codes have no resemblance to their IATA counterpart due to this. 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 E designating Western Europe, and G designating it a UK airport.
EYVI represents Vilnius airport in Lithuania (IATA: VNO), with E designating Western Europe, and Y indicates that it is in Lithuania.

To summarize, four-letter ICAO codes have a more rigid structure, with the first two letters 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 they will depend on each and every airport.