Two different systems, two different jobs
IATA codes are three letters, assigned by the International Air Transport Association, and exist for commercial purposes — booking systems, baggage tags, and the departure boards passengers actually read. ICAO codes are four letters, assigned by the International Civil Aviation Organization, and exist for operational purposes — flight plans, air traffic control, and official aeronautical charts.
How to tell them apart at a glance
Letter count is the fastest tell: three letters means IATA, four means ICAO. Beyond that, ICAO codes are built region-first — the first one or two letters identify a country or region before the airport itself, which is why they cluster predictably.
| Airport | IATA | ICAO | Pattern |
|---|---|---|---|
| JFK, New York | JFK | KJFK | Continental US ICAO codes start with K |
| Heathrow, London | LHR | EGLL | UK ICAO codes start with EG |
| Haneda, Tokyo | HND | RJTT | Japan ICAO codes start with RJ |
| Changi, Singapore | SIN | WSSS | Singapore ICAO codes start with WS |
Why they don't always look related
Sometimes the two codes share letters in an obvious way — LHR and EGLL both nod to "L" for London — but plenty of pairs look nothing alike. Chicago O'Hare is ORD (IATA) and KORD (ICAO), which lines up neatly, while Paris Charles de Gaulle is CDG (IATA) and LFPG (ICAO), where the ICAO code reflects France's regional prefix rather than the airport's initials.
Where you'll actually see each one
If you're booking a flight or reading a departure board, you're looking at an IATA code. If you're reading a pilot's flight plan, an air traffic control transmission, or an official aeronautical chart, you're looking at an ICAO code. Most major airports have both — a small number of very small or military-only fields have only one or the other.
Using this in Aviatle
Both codes are always accepted as a valid guess in Airport mode — you don't need to know which one to type, just whichever one you happen to remember. The final clue in every airport round reveals both side by side, which is a fast way to build up a mental library of the pairs over time.
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