What happened
While operating at approximately 550 ft, the pilot of the helicopter experienced a low main rotor RPM warning. In response to this warning, the pilot initiated an autorotation procedure. During the subsequent landing, the aircraft rolled onto its left side.
The investigation
The investigation focused on the circumstances leading to the activation of the low rotor RPM warning system. However, due to the extensive damage sustained by the helicopter during the accident, investigators were unable to assess the integrity of the aircraft's systems prior to the event. As a result, the specific reason for the loss of main rotor speed could not be established.
Findings
- The cause of the main rotor low RPM warning remains undetermined.
- The pilot was wearing a noise-cancelling headset at the time of the occurrence. The investigation noted that the use of such equipment may have masked abnormal engine or mechanical sounds that could have alerted the pilot to changes in the aircraft's operation before the warning system activated.
- The pilot indicated that without the noise-cancelling headset, ambient noises might have allowed for the detection of deviations from normal operating sounds.