On the 747, I believe the main landing gear wheels can be turned in the opposite direction to the nose wheels, to reduce the radius of turn and tyre scrub when taxying. Can anyone confirm this, and does it apply to all marks of 747?
Correct. But it's only the Body Gear that is steerable (the two rearmost trunks). The Wing gear (the outboard ones that are set a bit more forward) is fixed (steering wise that is...).
Ground engineer I once met told me that on a certain airfield in South America the aircraft had to make a 180 at the end of the runway to backtrack to the terminal but the concrete circle would only accomodate this with a ground engineer at the body gear pulling on the steering cables to get the wheels turned as far as they would really go!