Here's how it works for vehicles.
If you're ON friendly concrete, you should get a "safe" landing every time -- should, there's the odd report that at times it doesn't.
If you're closer to a friendly base than an enemy base -- and this includes out in the wilderness -- you will get a safe landing as long as nobody is around. I mean NOBODY. If there's so much as one person within x miles of you, it's a ditch. I think you might even be able to tower out safely at an enemy field, as long as there's nobody around.
Somebody did a lot of testing way back when Stalin's Fourth was run, because we were using GVs often in it.