Accident Sequence
The helicopter pilot was transporting snow skiers when he landed on a 20-degree slope below a mountain peak. With the engine running, he directed a guide and two skiers to unload. During this process, the pilot observed loose rocks falling from the peak above into the main rotor disk. After the three individuals were clear, the pilot raised the collective and brought the helicopter into a hover. No controllability issues were noted during the hover.
The pilot then repositioned the helicopter up the mountain about 30 feet and "toed in" to unload additional skiers. Once all remaining skiers had disembarked, the pilot began flying down the mountain to shut down and examine the main rotor blades. Approximately 10 seconds into the flight, the helicopter started shaking violently. The pilot initiated a forced landing. At about 150 feet above the trees, the flight controls became progressively difficult to maneuver, and the helicopter pitched nose-up. The pilot immediately lowered the nose and collective. When the helicopter was about 30 feet above snow-covered ground, the main rotor disk struck trees, and the helicopter impacted the terrain.
Damage
The helicopter sustained substantial damage to the main rotor blades, fuselage, tail boom, and tail rotor blades.
Mechanical Condition
The director of operations reported that no preaccident mechanical failures or malfunctions existed that would have precluded normal operation.