It's quite clear to me:
The helicopter was flying low in the valley.
This a sign that there was "no problem" until the rotor struck a tree.
After the impact the rotor became deformed and lost some of its aerodynamical characteristics.
But the most important is that the rotor also lost it's "weight balance".
This caused vibrations and oscillations to the movement of the helicopter.
Collin could not handle such a situation while flying in low altitude inside a valley.
And then the crash came ...
"Cyberacer"
my GP4 worksvideos of GP4 with 2009_Physics_and_V8Torque(18000rpm)Music bands I listen to:
C:REAL and
KELDIAN