Originally Posted by
A Squared
From a physics standpoint, it is completely meaningless. You are making the identical mistake that Ian was making. In your Scenario A, From the frame of reference of the ground, the airplane went from a velocity +110 knots to a velocity of -90 for a total change in velocity of 200 knots.
Say there's no wind (it's one of those perfect mornings) and you're flying around. You fly East for a while at 100 knots airspeed, and turn around and fly West. By that same premise, your airspeed is now -100 knots too, for a total change of 200 knots. Hmmmmm?
(if there's no wind then the airmass frame and the ground frame are the same, so you should just be able to do a find-and-replace of "ground" with "air" to your post and everything still hold true.)
No, it's perfectly valid, for certain contexts, to rotate the axes as needed.