What happened
During flight, the helicopter experienced a sudden reduction in engine power, forcing the pilot to execute an emergency landing. Flight data analysis confirmed the aircraft was positioned over inhospitable terrain when the power loss occurred. The pilot attempted to navigate toward a suitable landing area and initiated an autorotation. During this maneuver, the aircraft drifted downwind, reaching a maximum airspeed of approximately 70 kt before the pilot reduced speed to nearly 48 kt. This reduction was intended to facilitate a flare to slow the aircraft and increase rotor RPM prior to touchdown. However, the pilot reported a minimal flare effect upon approaching the landing site, which was attributed to low rotor RPM. Consequently, the helicopter struck the ground during the landing sequence. There were no injuries reported among the occupants.
The investigation
The ATSB investigated several potential causes for the engine power reduction, including carburetor icing, fuel contamination or starvation, handling errors, and mechanical defects. Evidence ruled out weather-related issues, fuel problems, and pilot handling as primary causes. Instead, information provided by the engine manufacturer and post-accident examination findings indicated that a pre-existing crack in the exhaust collector likely caused the reduction in engine power output.
Additionally, the investigation looked into the maintenance history of the helicopter. The ATSB noted that the aircraft's low utilization might have necessitated specific storage or maintenance protocols to prevent component corrosion or contamination. While there was no direct evidence that a lack of such maintenance caused the exhaust crack, the investigators could not definitively rule out its influence.