airborne

This is my first working TF2 map I've created that actually works as a gamemode. As you can see, I attempted at making an aircraft map (it doesn't really look like one at the moment) and you will definitely die if you walk off it. There are walls (surprised?) to prevent pyros from...

I'm not going into much detail, simply I need a phys_thruster to be disabled when its airborne. The position of it is randomized around the map, so I can't do a trigger around the entire ground. I don't think its possible, so is there any workarounds to this?