Incident Overview
A helicopter engaged in aerial filming for a motion picture was conducting passes over a volcano vent crater and its associated smoke plume. According to the pilot, during the third pass over the crater, he observed a decrease in main rotor RPM and the illumination of the rotor caution light. In response, he lowered the collective, which inadvertently led the helicopter into the volcano's smoke and steam cloud. After executing a turn, the aircraft exited the cloud and initiated an autorotation to the crater bottom.
Sequence of Events
During the flare portion of the autorotation, the main rotor struck the shear rock wall of the crater, causing the rotor to separate from the helicopter. Two camera operators who were onboard provided accounts of the incident. They stated that the pilot announced "we've got a problem" as they entered the smoke cloud. Both witnesses reported that they did not hear the low rotor warning tone and perceived no change in engine sound throughout the event. One camera operator additionally noted feeling "sideward yawing motions" during the descent. Both camera operators confirmed that after the helicopter emerged from the cloud near the bottom of the crater, the rotor struck the rock wall.
Observations
The pilot's actions and the helicopter's entry into the volcanic smoke cloud followed the detection of decreasing rotor RPM and the activation of the caution light. The subsequent autorotation and rotor strike ended the flight. No further details regarding the aircraft, occupants, or aftermath are provided in the source.