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Three letter combinations gives $26^3=17576$ possible codes. Some airports have multiple codes (ARN = STO, for example).

I’m just going to guess that there are more than 17576 airports in the world. Are we reusing these codes?

Him
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Filip Haglund
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    Actually, in the case with ARN and STO, STO is not specifically for Arlanda, but for "all" airports in the Stockholm metropolitan area (BMA). – Waked Sep 30 '15 at 13:23

2 Answers2

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In short, the people sitting over the nose wheel use the ICAO codes, and the people in the back use the IATA codes.

The IATA is the International Airline Transport Association. The ICAO is the International Civil Aviation Organization. While you are correct, the IATA does not have more than 17500 codes, their primary concern isn't creating codes for every airport including grass strips and private airfields. It is easy to think of IATA codes as being concerned essentially with identifiers that the passengers will need.

As far as ICAO is concerned, they contain a country identifier in their codes. They can even be more than 4 digits, as in the case of RU-2244 (Ukrainka Air Base). The vast majority are 4 digit or 5 digit, with the first 1 or 2 as the country code.

This allows ICAO to be available for every airport in the world. It is very common to refer to the IATA codes when flying locally, let's say within the USA, and refer to the ICAO if flying internationally.

I have a database structure of all airports in the world (or at least all known ones). This includes any grass/water/helipad/paved runways.

There are a total of: 46,465 airport/airfields including those that have been closed.

Source: http://ourairports.com/data/

Charlie
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  • Hm, I wanted to say that I recently noticed at least two airports that were missing from ourairports (and recently means a couple of months ago), but they were both added since. – Jan Hudec Sep 30 '15 at 13:05
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    As a side note, many airports in the U.S. do not have ICAO codes (or IATA codes,) but only FAA identifiers. Scheduled passenger service airports normally have all three, busier GA aerodromes normally have ICAO and FAA, GA aerodromes with less traffic normally only get FAA. – reirab Sep 30 '15 at 15:11
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As of June 2015, fewer than 2500 IATA codes have been assigned. Codes can be reassigned over time. According to the Wikipedia article on IATA codes there have been several IATA codes that have been reassigned. IATA has a mechanism for assigning these airport codes that's available online. Although your original calculation came to some 17000 possible codes, there's a wide variety of reserved codes, and prefixes, so it's actually less than 17500.

Sargun Dhillon
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  • Actually, it's MORE than the 17000 calculation, even with reserved, as numbers are allowed too. – Brian Knoblauch Sep 30 '15 at 15:02
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    @BrianKnoblauch In IATA codes? Are you sure? I know they're used in ICAO and FAA codes, but I've never seen a number in an IATA code. The wiki for IATA codes seems to suggest that they're letters only, but, of course, wiki isn't always right. – reirab Sep 30 '15 at 15:08
  • @BrianKnoblauch Unfortunately, according to IATA documentation, I can't share the numbering restrictions, but at least on first reading, it appears to be a subset of A-Z. – Sargun Dhillon Sep 30 '15 at 16:06
  • @SargunDhillon, can you link to the IATA documentation or at least add the section identifiers so others can look them up independently? – FreeMan Sep 30 '15 at 16:22
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    @FreeMan https://www.iata.org/publications/pages/coding.aspx - it's $545 – Sargun Dhillon Sep 30 '15 at 19:15
  • @SargunDhillon - nevermind... :( – FreeMan Sep 30 '15 at 20:01