I'm working on an idea for Sandbox in Sketchup, but I need to know wether Banshees/Hornets can fly from the normal level up to the Skybubble and back. Or is their a height limit for the normal level, and a bottom level for the skybubble*? *Or do you just die when you go too low, like you would without flying vehicle?
If you're on the middle level (the standard build level) then there is an invisible barrier very high up when in any flying vehicle. If you are in the Sky Bubble, then going below the level of the Forging grid causes you to die, even if you are in a vehicle. I think there is a slight gap between the upper limit of the middle layer and the grid level of the sky bubble, but this doesn't make much practical difference. So basically, it's not possible, sorry.
I tried to do the same too, the sky bubble is pretty limited with vertical flying space so I abondonned that plan and now I'm doing something else.