Airport codes are shorthand identifiers, but there is more than one system. The three letters on a boarding pass serve a different purpose from the four-letter identifier used in many flight-planning documents. Knowing which system you are looking at prevents a common mix-up.
IATA codes: the passenger-facing system
IATA assigns three-letter location identifiers used in commercial airline travel. These can represent airports, metropolitan areas and some intermodal locations. JFK identifies John F. Kennedy International Airport, for example, while a metropolitan-area search code may include multiple airports.
The IATA location-code fact sheet explains that airport and city codes are related but distinct. An airport’s code may reflect its name, city or historical identity. It is not safe to assume that the first letter of a three-letter IATA code tells you its country.
ICAO identifiers: four letters for operations
ICAO location indicators serve operational uses and have four letters. Many airports in the contiguous United States use K followed by their familiar three-letter identifier: JFK becomes KJFK. That pattern is not a universal conversion rule. Alaska, Hawaii and other regions have different arrangements, and some airports’ identifiers differ across systems.
The K and C prefixes often discussed for U.S. and Canadian airports belong to the ICAO framework, rather than to a rule that U.S. IATA codes start with K. Mixing those systems was an error in the earlier version of this article.
FAA identifiers are another reference
FAA location identifiers cover U.S. facilities, including many airfields without scheduled airline service. Some match the familiar passenger code; others are alphanumeric or otherwise different. Pilots use the identifiers appropriate to the chart, flight plan and system involved.
Check the airport before booking
Use IATA’s official airline and airport code search when you need to confirm a travel code. Then check the airport’s name and location in the booking. A city can have several airports with very different ground-transfer times. Matching the city name alone is not enough, especially when arranging a connection on separate tickets.