French low-level military routes
OK, I really don't get this. These routes criss-cross France, generally marked as 800-1500ft 'ASFC', which means 'Above Surface'. My question is what exactly this means. In the Massif Central there is one of these routes which perpendicularly crosses a 3,000 feet deep V-shaped river valley. Does this mean the route dives to follow the contours of the valley as it crosses it, following a trajectory which no aircraft on earth, military or civil, could follow?
Surely not. Can anyone explain this to me?
QDM