Aviation in Second life can be a deeply frustrating experience. The other big issue besides unlimited-height security orbs is no object entry parcels. Unlike ban lines, no object entry applies to the parcel at all altitudes. If you encounter a no-object-entry parcel, your vehicle stops immediately, and its physics are altered to remove any motion or forces applied to it. The practical effect of this is that an airplane stops in midair, and there's no way to get it flying again: even editing it so that it would move away from the no-entry parcel just makes it hang in midair, so you wind up having to unsit and delete it. As with security orbs, there's no way to know in advance that you're about to have this problem.
I would like to see the no object entry attribute limited to the same effective height as ban lines. Ban lines can be seen in advance and avoided at altitudes where they are effective (especially with some third party viewers that show nearby banned parcels on the minimap). If I'm flying above the ban line height limit, this would no longer be an issue with that change in place.