What happened
During flight operations, the aircraft experienced an abrupt loss of engine power at approximately 300 feet above ground level (AGL). The pilot immediately initiated a descent, maintaining airspeeds between 60 and 70 knots. Utilizing autorotation, the pilot successfully landed the helicopter on a dirt road.
During the landing sequence, the main rotor blades struck the tail boom, resulting in damage to that section of the airframe. The pilot reported that the density altitude at the time of the incident was over 9,000 feet, a condition that significantly impacts engine performance and lift generation.
The investigation
A detailed teardown of the helicopter's engine was conducted to determine the root cause of the power loss. The inspection revealed that the spur adapter gearshaft, part number 6899196, had failed at the forward splines. This mechanical failure is identified as the primary cause of the sudden engine stoppage.
Findings
The investigation highlighted several critical factors contributing to the incident:
- The failure of the spur adapter gearshaft led directly to the loss of engine power.
- High density altitude conditions (over 9,000 feet) likely exacerbated the performance degradation following the mechanical failure.
- The pilot's decision to execute an autorotative landing prevented a more severe accident, although it resulted in contact between the main rotor blades and the tail boom.