If I change an .air file in a FS2002 airctaft folder, is it necessary to change any refernces in the .air file for the model (.mdl) file? Thanks,Bruce.

All the references to the .mdl are held in the aircraft.cfg. In most aircraft there is no need for a direct reference to the .mdl itself as long as it is installed in the standard location (look at any of the default aircraft).That said the aircraft.cfg also holds geometric details of the model such as the positions of the landing gear, lights and scrape points - you will probably find that if you swap the .mdl or aircraft.cfg that these will not match up.I am not an FDE expert, but I am pretty sure that is correct !!

Thanks, I appreciate the advice.Bruce.