There are lots of places in Europe where CAS has a base marked like that, and below it is Class G.
So one has a 1500ft gap of Class G.
My Q is how closely does the Class D
base follow the contours below it? If the terrain changes from say 3000ft AMSL to 10000ft AMSL then the base of the Class D will fluctuate between (roughly) 6000ft and 11500ft, and I don't really see a 737 following that
Or any other aircraft for that matter.
When in the past I flew VFR through such regions (Italy comes to mind) I would just fly 1500ft above the highest obstacle within say 20-30nm, and didn't have any trouble. But that could have still been infringing Class D.
Is there some international rule for where the base of such airspace really lies? Do they take the highest peak within say 10nm?
One could get an idea by looking up airways in the area and look at their MEAs, but that isn't something you would expect of a VFR pilot... it also doesn't tell you anything about the base of the CAS.