Have you found any missing airport codes from Flight Tracker in Dashboard? So did I, specifically MBS, our local international airport. So I just went about adding it in hopes that the backend database that it connects to had it listed ... which it did. Here is the fix I used for adding MBS, but the inserted line could be for any airport code.
In a terminal window you, will need to use su or sudo to edit the following file: /Library/Widgets/Flight Tracker.wdgt/AllAirports.js. Since I wanted to keep the list in alphabetical order, I added the following line after the entry for the Miami airport:
{city:"Midland/Bay City/Saginaw",country:"MI",code:"MBS"},
The basic layout is:
{city:"City Name",country:"STATE_OR_COUNTRY_CODE",code:"AIRPORT_CODE"},
Then all you need to do is close and restart the Flight Tracker widget, and you have MBS as an option now.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050518114908332