Beware of using add-on aircraft as AI ones. Firstly, it can seriously affect frame rates. Secondly, unless the aircraft has been created in GMAX, it will not behave properly i.e. landing gear and flaps will not work properly.
A couple of groups on the net are working to create aicraft specifically for use as AI aircraft, alternatively, there are many repaints for the default aircraft.
I have lots of these, but have no time to do anything with them!!