Note: you can only edit the aircraft.cfg for that AI aircraft to meet the ground, for AI ONLY. For online games, if you see a cessna 20ft off the ground, don't panic, that person is flying an aircraft that you do not have in your aircraft list. Yet another Microsoft bug (I collect bugs

).
You can't do anything to fix it, except download all the available aircraft on the web and install to your hopefully massive harddrive, which I suspect no one in their right minds would do..
I once saw a Cessna172 do a flyby over my head at Mach 2, because he was flying the X-Wing.. Of course, that aircraft, never touched the ground, in my simulator..