Thanks for the replies folks. Problem is that I was thinking of the context of driving a simulator instrument and the software wouldn't understand "academic". Track I can handle because that's frequently undefined (stationary on the ground for example), but I am sure I was taught there was an arbitary way of defining heading in these circumstances - vague memories of something as simple as "where the pilot's legs are pointing". Of the top of my head would it be relevant if a pilot was flying an aerobatic display and needed to know at what point to stop a vertical rolling manoeuvre so that when they leveled out they would be on the correct heading?
