To answer the question posed earlier, would a skydiver be able to hear an approaching aircraft ?
In my limited experience (7-8 canopy descents) absolutely you could hear one coming while under parachute, its amazing what you can hear up there with nothing to deaden sound between you and the source, traffic on the ground and aircraft flying nearby easily. Ive heard tandem passengers screaming under canopy from the ground many times. (My house is less than a mile from the the local DZ)