ICAO Airport Codes and What You Need to Know About Them

Normally, all airport codes are of three letters. For instance, the Delhi Airport of India is named as DEL. However, those are codes used by IATA and in use since the past few decades by major international airlines. On the other hand, there is another set of codes, which are given out by the International Civil Aviation Organization.

What are the ICAO codes?

The ICAO (International Civil Aviation Organization) is the four-character code of airports around the world. These codes are different from the IATA codes. The codes were introduced in 1947 with the formation of the International Civil Aviation Organization under the United Nations. The airport authorities only uses ICAO codes with pilots for purposes like air traffic control, flight-tracking services, and communication. ICAO codes are based on the designated letters to region and country. The primary aim of ICAO codes is to provide clear and simple airport identification for aviation organizations.

This is in contrast to what we see with IATA codes that mainly help pilots, airlines and passengers locate airports easily and aid in baggage transfers and an easier airport recognition.

ICAO Code Structure

How us the ICAO code structure different? The complete system is divided into four characters, which is based on Hierarchy.

1. First Letter

First letter represents a group of countries within a continent. For instance, Gulf countries are designated O.

2. Second Letter

Second letter represents represent the country with in the region. However, if the country is larger than the country has various second letter identifying different region within the country. Like India has four different second letter.

3. Third and Fourth Letter

Rest of the two is used to identify the airport with in the city or small area.

Just using the ICAO code one can identify the location of the airport such as Heathrow is EGLL, that states Airport is within country UK and in London city.


For administrative or political reasons, there are few alterations in the way ICAO code is used for an airport.

- At present, letters I, J, and X are not in use as first letter.

- In a country like Russia, X is used for government, military or experimental airports. They have their own codes for internal use and do not carry any international code.

- Q is used only for International communication and other non-geographical purposes.

- In some cases three letter ICAO are used such for Edmonton International Airport, Edmonton; Alberta is YEG instead of CYEG. In some cases, it may go down to two letter such as for Hawaii and US territories.

- ZZZZ is reserved as special code when no ICAO code exists for an airport, but it is limited only in flight plans.

The ICAO is important today for enabling air traffic controllers to monitor flights in an efficient manner and solve problems related to flight tracking.