Another note if you want to use an external skin then the skin must be in the main game folder ( where the script *.c files are) or you must use PATH's or pragrma_path to set a path for the engine to find it. The engine loads skins, .mdl's do not have imbedded texture file paths like *.fbx or other formats and trust me this is a good thing.
HOW CAN I CHANGE THE PAN, TILT AND ROLL ANGLES OF AN ENTITY WITHOUT CHANGING THE DIRECTIONS OF ITS LOCAL AXES
Create an INVISIBLE model the max size and shape of the jet. Set the jet to PASSIBLE. Use vec_set() to tie the jet to the invisible collision object every frame. You are now free to rotate the jet and the invisible collision model need only be pan rotated and will act as the collision object. You will now be moving the collision object and the jet will automatically be connected.