From X-Plane SDK
XPLM_API void XPLMSetAircraftModel( int inIndex, const char * inAircraftPath);This routine loads an aircraft model. It may only be called if you have exclusive access to the airplane APIs. Pass in the path of the model with the .acf extension. The index is zero based, but you may not pass in 0 (use XPLMSetUsersAircraft to load the user's aircracft).