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I'm a new student, and I see the US airport codes on charts with the K prefix, e.g. KORD for Chicago O'Hare.

I have always seen on commercial flight booking sites, only the last three, letters such as "ORD" are displayed.

Are pilots meant to pronounce the full code or just the letters after the prefix, assuming the K prefix, when talking with ATC?

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  • $\begingroup$ Note the US, Canada, Australia and a number of islands are exceptions to the ICAO code prefix system. In other countries the ICAO code doesn't really match the IATA code (which is only used for commercial matters). The former begins by a "continent" code (e.g. L for Southern Europe), a country code (e.g. F for France) and ends with a local airport code. CDG is the IATA code for Paris Charles De Gaulle, but the ICAO code is LFPG (P for Paris FIR), similarly Paris Orly is coded ORY and LFPO. $\endgroup$
    – mins
    Dec 27, 2016 at 18:41
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    $\begingroup$ @mins In the U.S., there's a separate system. Not all U.S. aerodromes have an ICAO identifier, but all of them have an FAA identifier, which is typically 3 letters for larger public use airfields, 3 alphanumeric characters for smaller public use airfields, and 4 alphanumeric characters for private ones. While ORD is indeed the IATA code for O'Hare, it's also the official FAA identifier for O'Hare. For U.S. airports that have an IATA code, it usually matches the FAA identifier. For U.S. airports that have an ICAO identifier, it's usually the FAA identifier with a 'K' or 'P' prepended. $\endgroup$
    – reirab
    Dec 27, 2016 at 19:02
  • $\begingroup$ @reirab: Interesting, so for ATC purposes we use the ICAO code, and never the IATA code. In the US, FAA playing the role of ATC regulator has assigned FAA codes to be used in place of ICAO codes. They happen to be the same than IATA codes when there is one. In addition prefixing FAA code with K/P gives the ICAO code...? $\endgroup$
    – mins
    Dec 27, 2016 at 19:18
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    $\begingroup$ @mins Yeah, that's basically how it (usually) works. K is the continental U.S. while P is Northern Pacific region (e.g. Hawaii, Alaska, Guam, Saipan, etc.) I'd assume that the primary reason for the separate system is the enormous number of aerodromes in the U.S. They peaked at a bit over 20,000 in 2007, while K + 3 letters only gives 17,576 possible combinations. This graphic kind of puts it in perspective, though it doesn't appear to include helipads or seaplane ports. $\endgroup$
    – reirab
    Dec 27, 2016 at 22:11
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    $\begingroup$ @jamesqf I have used the codes in ATC comms, either of my own volition or by request, typically to clarify which airport I am asking for clearance to, or similar. $\endgroup$
    – J W
    Dec 28, 2016 at 15:41

7 Answers 7

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There are actually two separate coding systems in play here.

IATA (International Air Transport Association) codes are 3 letters and are used for commercial bookings etc. They are assigned only to commercial airports throughout the world. ORD is the IATA code for Chicago O'Hare.

Pilots and ATC use the four letter ICAO (International Civil Aviation Authority) codes, which are assigned to every public-accessible airfield in the world. These are systematically allocated with the first one or two letters indicating the country. K is used as the first letter of airfields in the continental US (with separate codes for Alaska, Hawaii & territories in the Pacific/Caribbean matching regional standards).

Commercial airports in the continental US tend to have the two codes in matching pairs such as ORD/KORD, LAX/KLAX etc but this is not the case in other countries. Manchester, UK has IATA code MAN but ICAO code EGCC.

Meanwhile smaller airfields in the US may only have an ICAO code, where the corresponding IATA code (minus the K) could belong to an international airport elsewhere in the world (for instance KPRG is Edgar County Airport, Illinois and PRG is Prague Václav Havel Airport, Czech Rep.).

Finally, the very smallest airfields in the US (typically private/restricted access fields, in any case not large enough to warrant an ICAO code) are given a 3- or 4-character code by the FAA which extends the ICAO system by allowing digits as well as letters. Small public fields have a 3 character code (eg 9S2 or C97) while private fields have 4 characters which typically include the state abbreviation eg TX05.

For more details of the exact determination of which code type a US airfield is assigned by the FAA, see reirab's excellent self-answered question: How does the FAA determine which format of location identifier to assign to an airport?

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    $\begingroup$ Actually, the K prefix only applies to the continental US. Alaska and Hawaii are part of the Pacific region code. Alaska airports start with PA. Anchorage (IATA ANC) is PANC. Hawaii airports start with PH. Honolulu (IATA HNL) is PHNL. $\endgroup$
    – Gerry
    Dec 27, 2016 at 14:28
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    $\begingroup$ IATA is the International Air Transport Association. It's an airline industry trade group. Also, all U.S. registered aerodromes have an FAA identifier. ICAO ones are mostly only assigned to airports that have scheduled passenger service and/or a non-trivial amount of international traffic. $\endgroup$
    – reirab
    Dec 27, 2016 at 18:55
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    $\begingroup$ I don’t know if it is a correlation or causation, but almost all airfields with a three letter identification (and therefore an ICAO code) have weather reporting capability. Almost no fields with digits in their code have weather. $\endgroup$
    – JScarry
    Dec 28, 2016 at 1:01
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    $\begingroup$ @JScarry Rather than answer in a long comment, I decided to write a self-answered question for this: How does the FAA determine which format of location identifier to assign to an airport? $\endgroup$
    – reirab
    Dec 28, 2016 at 21:28
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    $\begingroup$ @reirab I've incorporated a link to your new question in the body of my answer, hope that's OK. $\endgroup$
    – IanF1
    Dec 28, 2016 at 22:42
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The other answers have lots of excellent context & background info, but to give the direct answer to the direct question, *no, you don't use the "K" * with ATC under normal circumstances.

The (rare) exception will be when it is necessary for some reason, but that is almost never. In voice communication, "direct Midland VOR" or "direct Midland airport" are used, rather than "direct MAF" or "direct KMAF". Obviously, printed NOTAMS and flight planning work differently.

If you were to be cleared "direct MAF" (which is both the 3-letter FAA ID for Midland, and also the non-colocated VOR), it would be appropriate to query "is that the airport or the VOR?" if you aren't sure. (If you are navigating VOR to VOR to MAF & beyond, you could safely assume the VOR; if your destination is Midland, asking the controller would be appropriate.)

But when asking you to "say destination," it's understood you're landing at the airport rather than the navaid out in the field!

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    $\begingroup$ Well, shouldn't you extend it to "no, you don't use the "K", but you don't use the other three letters either"? Because that's the point—you use the name, not the identifier. $\endgroup$
    – Jan Hudec
    Dec 27, 2016 at 20:46
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    $\begingroup$ The name is most common, but there can be times when you're asked to "say destination", and if it's far enough away that the controller isn't familiar with the name, then you would give the 3-character FAA ID -- be it MAF or 9S2 or whatever. But KMAF would be unnecessary and it isn't the way I hear it on ATC. $\endgroup$
    – Ralph J ♦
    Dec 28, 2016 at 1:45
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As an FAA controller in the Terminal specialty (i.e. not an ARTCC controller) in the Lower 48:

NO.

No no no.

No no no no no no no no no.

NOOOOOOOOOOOOOOOOOOOOOOOOOO

You're a pilot in the USA. We're controllers in the USA. We don't need the Kilo. We don't want the Kilo. The Kilo is extraneous information that no one cares about when you're talking on the radio.

But more annoyingly than that, when you call asking for flight following we have to enter your destination using the FAA's three-letter code, no Kilo. If we enter four characters the system doesn't accept it. No bueno. Error. You will not go to space today.

So we're typing along, quick-quick-quick, trying to remember your type code (because in another annoyance, we have to enter your tail number, then your destination, then your type code, then your altitude, in that order and no other)—and you say you want flight following to KILO-PAPA-DELTA-XRAY and we type the K and then we have to backspace and type it out again and now it's a bad day.

So don't use it.

Please and thank you.

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The "K prefixed" and the "non-K prefixed" codes are actually different designation systems. The former is used by ICAO and the latter by IATA, and each have specific use cases by different authorities.

Not all airports in the world have their ICAO and IATA codes differentiated by leading K (an airport might not even have both). This is usually holds true only to the larger airports and only in the US. In case of airports in the rest of the world this is not true: some airports' ICAO and IATA codes are totally different from each other, while others' do bear some varying degree of similarity.

You can get an idea by looking at these lists: https://en.wikipedia.org/wiki/List_of_airports_by_IATA_and_ICAO_code http://www.flugzeuginfo.net/table_airportcodes_country-location_en.php

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    $\begingroup$ "Not all airports in the world have their ICAO and IATA codes differentiated by leading K" In particular, all the ones outside the US, since the K- prefix denotes an airport in the continental USA. $\endgroup$
    – David Richerby
    Dec 27, 2016 at 15:25
  • $\begingroup$ @DavidRicherby Indeed. "This is usually holds true only to the larger airports and only in the US" $\endgroup$
    – DeepSpace
    Dec 27, 2016 at 15:27
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    $\begingroup$ But it doesnt "usually hold true". It's completely specific to the USA. It's like saying "Not all countries in the world have a capital called Washington." $\endgroup$
    – David Richerby
    Dec 27, 2016 at 15:30
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    $\begingroup$ @DavidRicherby I think the 'usually' is regarding whether airports elsewhere are "some other letter + IATA code", which is true for some airports outside the continental US - mostly in Canada, and the "P"acific airports in the US as mentioned in another answer, and a handful of others worldwide. $\endgroup$
    – Random832
    Dec 27, 2016 at 17:09
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    $\begingroup$ IATA codes are not used when communicating with ATC. In cases where the FAA identifier matches the IATA code (nearly all major US commercial airports), the difference is transparent, but when things don't match up, IATA is used at the ticket counter but not on the radio. $\endgroup$
    – Ralph J ♦
    Dec 29, 2016 at 15:13
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When programming your GPS or FMS you need to distinguish between airports and VORs e.g. KLAX is an airport and LAX is a VOR on the airport. But controllers rarely say the letters and instead use the names for airports and VORs. It is usually clear from the context and the destination that the pilot has filed.

A typical clearance from my airport might be Crepe Three departure, Morro Bay transition, San Marcus then as filed. The pilot knows to follow the CREPE3 departure which terminates at MQO and then direct to FLW and from there whatever was filed.

When asking for VFR flight following, pilots usually just give the name of the destination airport unless there are multiple airports in the same city. For example, Bakersfield has two airports so to make sure the controller knows where you want to go you would give the identifier, either BFL or L45. Also, if you are going to a small airport outside of the local area the controller may not have heard of it and will ask for the identifier.

I don’t recall hearing anyone say the identifier with a K when talking on the radio. But that’s not necessarily something I’d notice. You might want to listen to some of the clearance delivery channels on LiveATC to get a feel for how pilots and ATC communicate routes.

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In my experience, you usually use the NAME of the airport (or navaid). Center controllers are well familiar with their AOR (and usually adjacent ones just by experience).

Now for longer VFR flights where you may be crossing multiple centers, they may not recognize the named airport, so giving them the identifier can be helpful. This is not an issue for IFR where they already have your full plan.

Finally, a 'little secret' is that the name an airport is called locally is often different than the name in your AFD. For example, Lewis A Jackson Regional Airport (I19) in Xenia Ohio is "Greene County" (not "Jackson Regional"). Calling the FBO on the phone before flight will uncover that, or listening on the radio as you approach. If unsure, go ahead and append the identifier to the name you guess it should be called. Yeah, you're chewing bandwidth, but that's more efficient than the back and forth and better than a mistaken ID.

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Usually, yes, and in particular when using the airport for position reporting. Sometimes there will be a VOR or VORTAC which uses the same three letter identifier nearby or collocated on the airport so it can cause confusion for a controller.

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