ICAO vs. IATA Codes: What's the Difference and Why Airports Have Both
Book a flight and you'll see three letters, like LAX. Read a METAR, a flight plan, or hear a pilot on the radio and you'll see four, like KLAX. Same airport, two completely different codes. Here's what each one is for, and why the system never merged them into one.
What IATA Codes Are
IATA codes are the three-letter codes you see on boarding passes, baggage tags, and booking sites: JFK, LHR, NRT. They're assigned by the International Air Transport Association, the trade body for commercial airlines, and they exist for one job: making air travel identifiable to passengers and bookable across airline and travel-agency systems. Because there are only 26 letters and three slots, some codes are reused across different airports over time, and a few are historical rather than literal, like ORD for Chicago O'Hare, a holdover from the airport's old name, Orchard Field.
What ICAO Codes Are
ICAO codes are the four-letter codes used in operational aviation: flight plans, METARs and TAFs, air traffic control, and charts. They're assigned by the International Civil Aviation Organization, the United Nations body that sets global aviation standards, and they're built for precision rather than recognition. Every ICAO code is unique worldwide, with no reuse, which matters when a controller or a pilot needs zero ambiguity about which airport is meant.
Why Airports Have Both
The two systems were built by different organizations for different audiences. IATA codes are commercial: short, memorable, and designed for a passenger-facing industry that needed a fast way to route baggage and tickets as air travel scaled up in the mid-20th century. ICAO codes are operational: longer, regionally structured, and designed for pilots, dispatchers, and controllers who need to identify any airstrip on Earth, including plenty of small fields with no scheduled airline service and therefore no IATA code at all.
How to Tell Them Apart at a Glance
Letter count is the fastest tell: three letters means IATA, four means ICAO. ICAO codes also carry a regional prefix. In the continental United States, nearly every ICAO code starts with K, so JFK becomes KJFK and LAX becomes KLAX. Canada uses C, much of the UK uses EG, Germany uses ED, France uses LF, and Japan uses RJ. Alaska and Hawaii are the common US exception: Anchorage is PANC and Honolulu is PHNL, both under the Pacific region's P prefix rather than K.
When Each One Is Used
If you're booking a ticket, checking a departure board, or tracking a bag, you're using IATA codes; that's the system the entire commercial travel industry is built on. If you're reading a METAR or TAF, filing or reading a flight plan, or listening to ATC communications, you're in ICAO territory. Weather reports in particular are always ICAO: a METAR is filed against the four-letter code, not the three-letter one, which is why aviation weather sources and flight-planning tools default to ICAO even when the airport is also a major commercial hub with a well-known IATA code.
AvClock's airport search accepts either code, but every saved airport, weather report, and clock row displays the ICAO identifier, matching the same four-letter codes used in METARs, TAFs, and flight plans, so what you see in the app lines up with what you'd see anywhere else in operational aviation.
AvClock is reference and informational only, not for actual flight planning or navigation. Always use official sources (FAA, NOTAMs, charts, ATC) for that.