The K prefix — contiguous US (CONUS)
ICAO assigns the letter K to the contiguous United States. To convert a 3-letter FAA identifier to ICAO, prepend K. To convert back, drop the K.
Airports that do NOT get a K prefix
The K conversion only applies to 3-letter FAA identifiers. Many smaller US fields have 3-character alphanumeric identifiers like 2G4 or N87 — these airports have no ICAO code at all. On an ICAO flight plan, file ZZZZ and specify the field in Item 18 (DEP/ or DEST/).
Alaska — PA prefix
Most Alaska airports use the PA prefix in the ICAO system (P = Pacific region, A = Alaska). A few fields carry PF, PO, or PP instead — for example PFYU (Fort Yukon) and PPIZ (Point Lay).
Hawaii — PH prefix
Hawaii uses the PH prefix (P = Pacific, H = Hawaii).
US territories
When to use which code
Since August 27, 2019, all US civil flight plans — domestic and international — are filed in the ICAO format (FAA Form 7233-4). Filing systems accept the 3-letter FAA identifier and resolve it to the ICAO code (or ZZZZ when none exists). METARs and TAFs use ICAO identifiers; US domestic NOTAMs are keyed by the FAA identifier (e.g. !JFK), while ICAO-format NOTAMs carry the 4-letter code in item A).
If you file via Leidos Flight Service (1800wxbrief.com), the system accepts either format. Most EFB and flight planning apps search both. AeroCopilot automatically resolves FAA and ICAO identifiers interchangeably.
Cite this
PermalinkAeroCopilot — FAA Airport Identifiers. https://www.aerocopilot.ai/tools/faa-airport-identifier.