I was bored yesterday so I tried to look up activity for Juneau and Ketchikan. I tried PJNU which was recognized but at the same time FA says invalid airport code and therefore no activity was recorded.
So I looked up the correct ICAO code and it turns out it is PAJN, JNU is the IATA code. But Flight Aware does not recognize PAJN as a valid code either so no activity is shown.
For some reason the 3 letter FAA or IATA code is not carried forward into the 4 letter ICAO format like most “lower 48” airports are. (LAX>KLAX)
Likewise Ketchikan should be PAKT not PKTN. Here are a few other correct codes:
Fairbanks: PAFA,
Nome: PAOM,
Kotzebue: PAOT
Unalaska (Dutch Harbor): PADU
Some of there are recognized but invalid at the same time so no activity shown.
I’m sure there are others, Anchorage and Kenai are the only totally correct ones I found.
complete list of ICAO codes here: