What happened
While conducting corn pollination operations, the pilot of the helicopter experienced an engine failure during a turn to reverse direction. This event led to a loss of main rotor RPM. The pilot attempted to recover by lowering the collective and rolling the throttle into the overtravel spring; however, these actions were unsuccessful in recovering from the low RPM condition.
The aircraft performed a hard landing, during which the main rotor blades severed the helicopter's tail boom. There were no injuries reported following the incident.
The investigation
An examination of the engine revealed low compression readings on the cylinders. Partial disassembly of the engine showed that this low compression was caused by loose carbon deposits located on the valve and seat surfaces. Investigators determined that this carbon was most likely knocked loose during the impact of the landing. No other anomalies or mechanical conditions consistent with a pre-mishap malfunction were observed during the engine examination.