I have a jet flying through my mountain range created in unity using the raise/lower terrain tool and there is no collision with the mountain walls nor peaks i placed a onTriggerEnter to debug the terrain and check what is colliding but my plane is not popping up any suggestions?
did you attach a terrain collider to the terrain?
Does your plane have a collider?
Click on your plane and go to Component -> Physics -> Box Collider. Your terrain should come with a terrain collider So you just need to add a box collider to your plane.
Your plane might be just to fast. This is the same problem I had and solved about a minute ago ;-) . If you have a Collider and rigidbody on both objects attached, it should be the speed. Try this here : http://www.unifycommunity.com/wiki/index.php?title=DontGoThroughThings
This worked to me :)