FFS. The plane takes off! Think about this. You know you've got a sheet of paper or a dvd underneath a pile of something/more dvds. And you whip it out, the pile above doesn't move out with the sheet of paper/dvd. This is because the friction between the paper and the pile is smaller than the air resistance(?). Applied to the plane. At low speeds, the treadmill would move the plane backwards (providing that the plane doesn't have it's engines on), but at high speeds, the treadmill (and the plane's wheels) would just spin but the plane would go nowhere. Too tired to caryy on but basically, for both scenearios, the plane would take off. Well. It should do. Maybe.