Does anyone know what happens if you fly below takeoff height?
Eg if I stand on top of a hill, then fly it down the side of the hill into the valley below?  Would the motors shut off, thinking it is trying to land as it is below the height it took off from?

It will explode in Mid - Air causing untold death and destruction.................... for Gods sake Rib don't do it !!...............................  No nothing will shut off or anything.  It will just show negative numbers though.  Your initial home point will be the 0 reading anything below will be negative numbers above of course positive.   

cheers ribfeast-donnie

And RTH will still make the P3 ascend to the RTH height above the home point.  So, if you're flying at -80 metres & RTH height is set at 30 metres, it'll ascend 110 metres to +30 metres altitude from the home point.

What about if you flew towards a NFZ?  You know how the height restriction tapers down like an inverted cone the closer you get to it?  Would it theoretically allow you to fly higher in that taper-off area than you normally could?

Ribfeast Posted at 2016-3-3 23:11
What about if you flew towards a NFZ?  You know how the height restriction tapers down like an inver ...

Yes, because it doesn't know its height above sea level or the height of the airport above sea level.  It assumes you're at the same height as the airport.

No issue at all. Your phantom will not turn off. I usually fly from a top of a mountain. All works.

Good to know, thanks all