What does the K stand for in KLAX?

It does not abbreviate a word. K is the ICAO region prefix assigned to the contiguous United States. The last three letters, LAX, are the airport's IATA code. So KLAX is just K plus LAX.

Why does the US get K as its ICAO prefix?

The letter comes from American radio history. Early US radio stations west of the Mississippi River received call signs starting with K, and east of the river got W. When ICAO built its four-letter global system in ICAO Document 7910, it adopted K for the contiguous US because the letter was already associated with American aviation communications and would not collide with other regions.

Do Canadian airports use K too?

No. Canada's ICAO codes start with C, so Vancouver's YVR becomes CYVR and Toronto's YYZ becomes CYYZ. That mirrors Canada's radio history the same way the US K does, since Canadian radio call signs begin with C.

Why Do US ICAO Airport Codes Start With K? The Radio History Behind KLAX and KJFK

Your boarding pass says DEN. Your pilot filed a flight plan to KDEN. That extra K is the entire difference between an IATA code and an ICAO code in the contiguous United States, and the reason for it is older than passenger aviation. It comes from radio.

In the early days of broadcasting, the United States split the alphabet at the Mississippi River: radio stations east of the river got call signs starting with W, and stations west got K. When the International Civil Aviation Organization built its global four-letter system, published in ICAO Document 7910, it assigned K to the contiguous US. For most American airports, the ICAO code is simply the three-letter IATA code with a K in front: Atlanta's ATL becomes KATL, Boston's BOS becomes KBOS, Miami's MIA becomes KMIA. The rule of thumb works for hundreds of airports, which is why it feels like somebody designed it. Nobody did. It was borrowed from radio.

That borrowing also explains the exceptions. Alaska and Hawaii were not part of the contiguous K block, so each got its own prefix: PA for Alaska, where Juneau is PAJN, and PH for Hawaii, where Hilo is PHTO. And small American fields that never received an ICAO code at all live under FAA identifiers, which can be three or four alphanumeric characters: 65S for Bonners Ferry, Idaho, or 2WA1 for Diamond Point Airstrip in Washington, where the leading characters are the state code. If the system looks inconsistent, that is because four different systems are doing four different jobs, and they grew up in four different decades.

The quick version: K means the contiguous United States in ICAO's region system. It almost always sits in front of the airport's familiar three-letter IATA code.

The weather station detour

The radio story has a step in the middle that people usually miss. Before airlines needed codes, the US National Weather Service used a two-letter system for its reporting stations. When airlines adopted three-letter codes, airports that had grown up around weather stations needed a third letter, and plenty of them just added an X. Los Angeles became LAX, or KLAX in the four-letter world. Portland, Oregon kept the X too. So one letter of your airport's code can trace to a 1930s telegraph office, and the letter in front of it traces to a 1920s radio dial. Airport codes are archaeology with a boarding pass.

So why K, and not something else?

Here is my honest read: the K was available, it was already associated with American aviation communications, and it could not collide with anyone else's codes. ICAO's first job was uniqueness. The IATA three-letter codes were already in use worldwide, so reusing them directly risked duplicates between countries. A region prefix solved it, and K solved it for the United States because a generation of radio operators had already learned that K means America. That is less romantic than a committee voting on symbolism, but I find it more satisfying. The most international part of your flight plan is a leftover from the era when planes navigated by listening to the radio.

ICAO prefix	Region	Example
K	Contiguous United States	KDEN (Denver)
C	Canada	CYVR (Vancouver)
PA	Alaska	PAJN (Juneau)
PH	Hawaii	PHTO (Hilo)
E	Northern Europe	EGLL (London Heathrow)
S	South America	SBGR (Sao Paulo/Guarulhos)

The same logic runs everywhere else on the map. Canada uses C for the same radio reason, northern Europe uses E, southern Europe L, South America S. The first letter locates the region; the rest locates the airport. Once you see it, flight plans read like an atlas.

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Frequently asked questions

Do all US airport ICAO codes start with K?
All ICAO-recognized airports in the contiguous US do. Alaska uses PA, Hawaii uses PH, and small fields without ICAO codes use FAA identifiers like 65S or 2WA1.

What does the K stand for?
Nothing, really. It is the region prefix ICAO assigned to the contiguous United States, borrowed from early American radio call signs. KLAX is K plus LAX, nothing more.

Do pilots use IATA or ICAO codes?
Pilots and air traffic control use the four-letter ICAO codes for flight plans and navigation. The three-letter IATA codes are the passenger-facing versions on tickets and baggage tags. We compare the two systems in IATA vs ICAO codes.

Can a US airport's ICAO code ever change?
Rarely, but it happens when airports relocate or merge. Our piece on whether airport codes can change covers the famous cases, and when IATA, FAA, and ICAO codes disagree covers what happens when the systems do not line up. Canada's version of this story, the Y codes, is here.

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Sources: ICAO Document 7910, Location Indicators; key.aero, "ICAO Codes explained"; airplaneacademy.com, "Why Do Some Airport Identifiers Begin with K?"; British Aviation Group, "Why US Airports' ICAO Codes Start With The Letter K". Figures verified October 2026.