Wiktionary
aeropause
n. The region of the atmosphere above which it is not possible for aircraft to fly
Wikipedia
Aeropause
Aeropause is the region in which the functional effects of the atmosphere on man and craft begin to cease.
Usage examples of "aeropause".
Somewhere up there in the aeropause, the fountain flattened into a shell of orbits encompassing the whole of He, and it was important to know how high up that shell began.