If you have used Traffic Tools to edit the Traffic.bgl file, then Traffic Tools should have created a backup file of the original called Traffic_ORIGINAL.bbb, which can be found in the following directory: C:/Program Files/Microsoft Games/fs2002/Scenedb/Atc/Scenery.
The original AI flight plans can easily be obtained by Decompiling this file. Before you do anything, make sure you copy your current Traffic.bgl file (found in the same directory as above) into a temporary folder so it can be restored later!
