To add some additional suggestions to crbascott's post above:
Add a Schedule dropdown menu to the airport select screen that allows the user to select a schedule. The list would be dynamically generated by reading schedule info files found in the airport directory. The schedule info files can be a simple text file that lists the Schedule name, schedule maker (FeelThere, ND, user, etc), schedule version, airport file (can be the global file), airlines file (global or custom), terminal file, and the flight schedule file. This would allow for multiple schedules, terminal files to exist in the airport directory. When Real Traffic is updated, it won't wipe out custom schedules. This will allow for users to easily add downloadable custom schedules from the community along with new schedules or historic schedules available as DLC from either FeelThere or ND or other content provider. This would allow users to switch to other schedules without having to replace game files. Version info would help resolve mutliplayer schedule issues. By default there will be the Default or FeelThere Schedule with its airlines. If you install ND Real Traffic then there would be an option for Real Traffic. We could get official schedules for different day, historic schedules with Pan Am, TWA, Eastern, etc).