Here is a video taken from the cockpit of a US chopper when the top rotor hits a tree....... good save from that pilot although he should have payed a little more attention to those trees. Watch the trees on the right side of the chopper.
http://www.avpics.de/mov/mil/64-tree.rm
And this one got a wind ghust while refuling. Very lucky crew.
http://www.avpics.de/mov/mil/probe.rm