I might be completely wrong here. I recently added my new test airstrip to the FS9 database to find out how all this works. I don't remember manually adding it to the TTools Airport text file. Try running CollectAirports.exe. I think this should do it automatically. Save the text file it creates under a different name & use this one to compile your new flight plans. :-/
Copied from TTools ReadMe.htm
CollectAirports is a separate program from TTools and is included in the same package. It will collect data for all of the airports in FS2004 or FS002, including add-ons, and will create a new Airports file listing those airports.
PS. This is TTools version 2.02 for FS9 & FS2002.
PPS. I just checked it out. For FS9 CollectAirports will create a file named Airports_FS2004.txt. Use this one instead of the original to compile your flight plans.