Forgive me for butting in on this, but I remember a holiday in the USA in about 1980 when we were in St Louis airport at 18:00 waiting for our flight. At 18:00 exactly, I saw several 727 planes reversing themselves away from the terminal, just like a bus station. The most incredible thing I saw at an airport. Presumably they were under some form of ground control but no need for a tug to push.