International Civil Aviation Organization airport code

The ICAO (/ˌaɪˌkeɪˈoʊ/, eye-KAY-oh) airport code or location indicator is a four-character alphanumeric code designating aerodromes around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators are used by air traffic control and airline operations such as flight planning.

ICAO codes are also used to identify other aviation facilities such as weather stations, International Flight Service Stations or Area Control Centers, whether or not they are located at airports. Flight information regions are also identified by a unique ICAO-code.

The International Civil Aviation Organization was formed in 1947 under the auspices of the United Nations, and it established Flight Information Regions (FIRs) for controlling air traffic and making airport identification simple and clear.

Code selections in North America were based on existing radio station identifiers. For example, radio stations in Canada were already starting with "C", so it seemed logical to begin Canadian airport identifiers with Cxxx. The United States had many pre-existing airports with established mnemonic codes. Their ICAO codes were formed simply by prepending a K to the existing codes, as half the radio station identifiers in the US began with K. Most ICAO codes outside the US and Canada have a stronger geographical structure.

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