What this relates to:
Cables or wires, trees, masts: the main or tail rotor blades collide with an obstacle on the ground during a helicopter operation and the helicopter is damaged.
Example:
A helicopter disembarks a person at a farm. The terrain is too steep for a landing, so the pilot moves the helicopter a few metres to the left. He comes too close to a tree and the force of the downwash pushes a branch away. After landing, the downwash reduces. The branch snaps back so far that some twigs and leaves touch the end caps of the rotor blades. Green marks are visible on the leading edge of the end caps.
