The question's terms of reference are vague. If we are talking about a homogeneous airmass then effectively we are talking about equivalent of a fly in a moving car or bus etc. It will have a 'strange' path across the ground but as far as it is concerned, it is flying from one side of the vehicle to another. But as soon as airmass changes speed or direction, or there is turbulence or shear layers then it becomes more interesting. Such as the detail about the 747 descending with strong tailwind, or low turns in a helicopter, or turns close to the ground in a glider following a cable break. I'm sure there is good maths to calculate what is safe and what is not. But there is also "pucker factor". Before I ever considered a low turn I always made sure I had plenty of airspeed. Anything above 0.1% PF had me worried.
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Last edited by Piltdown Man; 1st Feb 2017 at 10:08.