IATA codes consist of two letters, or one letter and one number, that identify specific airlines. Sometimes the letters reflect the airline name, such as AA for American Airlines. Other codes seem to have little connection to the airline, such as 4M for Lan Dominica and 5F for Arctic Circle Air Service.
ICAO codes consist of four letters that indicate the departure city or the destination of an aircraft. For example, the code for a flight to Serka, Afghanistan, is OASK. The first two letters are the code's designation for Afghanistan. The SK represents the city of Serka. In certain countries, the code letters represent individual provinces or states. For example, a flight to Fairbanks, Alaska, would be coded PAFA. The PA represents Alaska and FA is the designation for Fairbanks.The ICAO had 4,723 unique codes in October 2010.
The IATA also issues three-letter codes to identify individual airports. Many are based on a city's name. The code for Hartsfield-Jackson Atlanta International Airport, for example, is ATL. But others have no obvious connection to a city. For example, the code for Chicago's O'Hare International Airport is ORD. Travelers see the codes on their luggage tags, but they also are used in pilots' radio communications. The IATA and ICAO also issue codes for aircraft types. For example, the IATA code for an Airbus A-340-600 is 346. The ICAO code for that aircraft is A346.
