If an airport is from North America, then it starts with K and so on.

  • Where did ICAO get the letters from?

  • Why does the Philippines region starts with A?

  • Why do airports in Izmir have LTBx prefix?

  • Did they do some random letter ballot box?

  • Also why did they decide to make 27 regions?

  • Why does the Arctic have so many codes and why multi-letter codes? Honoring the countries that operate the adjacent runways to the science facilities perhaps?

I wanted to ask multiple questions but how they got names questions are about the exact same stuff and probably has the same answer, and the Arctic is almost exactly about the same topic too but I don't think it really needs a separate question.

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    $\begingroup$ "If airport is from North America then it starts with K" or P, C, B, L, M or T. $\endgroup$
    – Bianfable
    Commented Aug 27, 2019 at 17:50
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    $\begingroup$ Possible duplicate of What is the methodology for assigning airport codes? $\endgroup$
    – Rob
    Commented Aug 27, 2019 at 19:59
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    $\begingroup$ I don't see this question as a dupe. I think this question takes what's in the answers to the suggested dupe, and then goes on to ask, "ok, great, so now WHY did they decide to do it like THAT?" The "what they do" is given, the "why they chose that method" is what's asked here, and not really, IMHO, answered in that question. $\endgroup$
    – Ralph J
    Commented Aug 27, 2019 at 20:28

2 Answers 2


There is no one, easy answer for where each region (or country) got their one- or two-letter designation. Many of them evolved over time. When the ICAO (as an organizational body) was formed out of the international conference in Chicago in November 1944, dozens (or hundreds?) of things needed to be standardized between nations. One of these things was a standard way to identify airports. (Another was aircraft registrations... a minor, but related, blurb about that at the end.)

Many of these attending countries already had a "standardized letter prefix" from the 1912 convention in London regarding telecommunication call signs. For example, Canada was C (easy to understand why), and the United States was either W or K (less easy to see why, but there is history there, too -- see below). Other countries who were members to the 1912 convention had various call signs, some of which started with numbers. These countries, obviously, did not easily convert over to a letter prefix system that ICAO was adopting. At the end of the day, there were numerous ICAO committee meetings (and I can only imagine some heated arguments between delegates) that eventually resulted in the various regions and sub-regions we know today and that are depicted on the map below.

A small bit of history on how the USA evolved to the letter K: In the late 1800s, when telegraph was getting under way and Morse Code was in heavy use, there were two very easy to use Morse Code letters: A (dot dash) and N (dash dot). The US Government reserved these two letters for its military telegraph station call signs, and assigned A to the Army and N to the Navy. Makes some logical sense so far. Of course, the civilians were wanting to get in on the revolutionary breakthrough of wired (and eventually wireless) telegraphic communications, so the US Government created a civilian set of call signs in addition to the military ones. To do this, they simply added a single dash to each Morse Code letter, and the dot-dash (A) became dot-dash-dash (W) and the dash-dot (N) became dash-dot-dash (K).

The USA now essentially had four different letter-prefix designations for its radio station call signs: A and N (military use), and W and K (civilian use). The W and K call signs were also geographically separated with K being assigned to all stations in the west, and W for all stations to the east. The "border" between K and W changed over time, eventually landing on the Mississippi river, but that's another topic. You still see this today in your AM/FM music broadcasting and TV stations, with most stations "out west" being a Kxxx identifier.

Eventually, voice radios became very popular, and all new stations were only issued the letter K. W-stations were grandfathered in. Additionally, radio stations began to be carried onboard aircraft, and the previous military-only letter of N was eventually assigned to all airborne radios, including civilian. Aircraft began marking their exteriors with their N-xxx radio call sign.

Anyway, to make a long story short (too late?), the US was able to exert is muscle at the 1912 conference in London, and all 4 of those letter prefixes (A, N, W, and K) were retained for sole use to the US. But 35 years later, during the formation of the ICAO and the resulting subcommittees, the US agreed to be "Letter K" for its airport designations and "Letter N" for its aircraft registrations, losing the letters W and A (at least in the ICAO books). Also, remember that Alaska and Hawaii were not yet states, so they were both lumped into the Pacific Region [P] with sub-regional designations of PH and PA, along with all the other Pacific Region subs (PG for Guam, PM for Midway, PB for Baker, etc.).

ICAO Region codes and individual country codes

  • $\begingroup$ That history is for radio callsigns, which does explain tail numbers but appear to be completely unrelated to ICAO airport codes. That CONUS got the region code K could easily be a coincidence. Do you have a specific source that says otherwise? $\endgroup$
    – StephenS
    Commented Aug 28, 2019 at 14:27
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    $\begingroup$ Unfortunately, I cannot find a source at the moment. This all comes from my memory from a semester of ICAO history back in my AvMgt college days. However, the US had already been gravitating toward the letter K only for its broadcasting stations, and the ICAO prefixes were not only going to identify airports, but also other things like weather broadcasting stations. Since the US had many such stations already prefixed with K per previous international agreements, the US delegates easily argued to keep K as the US designation within ICAO. $\endgroup$
    – Jimmy
    Commented Aug 28, 2019 at 15:01
  • $\begingroup$ Even if that is true for CONUS, it does not appear to be the case for any other region. $\endgroup$
    – StephenS
    Commented Aug 28, 2019 at 15:15
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    $\begingroup$ @StephenS, ICAO codes are about more than airports. They’re assigned to many things, including airports. But every “thing” (recognized by ICAO) in the US-CONUS region (for example) is assigned a starting letter of K. That’s because, 60 years go, the US delegates to the convention lobbied for, and were granted, the letter K. They did so because the US had already been assigned K in other intl agreements, such as the ITU. It made sense to stay with K. Some regions weren’t so lucky and have a new letter issued from scratch. Other regions kept what they had from their ITU assignments. $\endgroup$
    – Jimmy
    Commented Aug 29, 2019 at 21:35
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    $\begingroup$ The bottom line is that ICAO codes for airports are VERY tightly linked to the history of radio station call sign prefixes. Many are the same, many are not, but the history of those radio codes goes a long way toward answering the question. $\endgroup$
    – Jimmy
    Commented Aug 29, 2019 at 21:47
  1. I'm not aware of any published rationale for the region codes. Some have a seemingly rational basis, e.g. C for Canada, but that may be coincidence. The country code, where applicable, is obviously related to the country name in most cases.
  2. See #1.
  3. Izmir is in Turkey, which has region code L (Southern Europe) and country code T (Turkey).
  4. See #1.
  5. There are 22 regions, one for each letter except for I, J, Q and X. I'm not aware of any published rationale for this number or list. However, Q and X are often reserved for special purposes, and I is often not used because it can be confused with 1. That last isn't consistent with the use of O, which can be confused with 0, rather than J, though.
  6. There is no region code specifically for Antarctica (I assume that's what you meant), and by treaty it cannot be part of any country, which is a case ICAO's rules don't address. Each country that builds an airport must therefore borrow a code from their home region(s).
  • $\begingroup$ Pardon my rather terrible sleep deprivation. I wanted to mean LT -B- J. I wonder why Izmir got B $\endgroup$ Commented Aug 28, 2019 at 17:05
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    $\begingroup$ You'd have to ask the DGCA that to be sure, but it appears all of Turkey's airport codes are LTAx through LTFx, so perhaps they simply assign the codes in alphabetical order? $\endgroup$
    – StephenS
    Commented Aug 28, 2019 at 21:03
  • $\begingroup$ perhaps simply dividing country through East to west and giving next letter if cities are different. $\endgroup$ Commented Aug 28, 2019 at 21:06
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    $\begingroup$ All the airports in Istanbul FIR seem to be LTBx and LTFx, while those in Ankara FIR appear to be LTAx, LTCx and LTDx. So, there may be some encoding of location there. $\endgroup$
    – StephenS
    Commented Aug 28, 2019 at 21:15

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