How do i check if vehicle has turn upside down

I am trying to detect whether the vehicle has turn up down(i.e top of chassis touch grass).I am thinking of something like "on collision with object at imagepoint" where i set the imagepoint on the chassis.However this condition doesn't exist.

demo here -> dropbox.com/s/bt9k1d5hab7auht/workingdemolatest.capx

Hello again. This should work, I put image point 3 on the gun turret, or at the top of the chassis.

You rock plinkie.......