Accident Sequence
The pilot reported that during cruise flight at approximately 900 to 1,000 feet above ground level, maintaining 95 knots and 80% torque, the helicopter suddenly lost altitude and yawed violently to the left. This was followed by a rapid roll, though the pilot was unsure of the direction. The event occurred without warning.
Pilot Actions
In response, the pilot initiated an autorotation to a field, maneuvering to avoid trees. During the flare, the pilot pulled collective, causing the helicopter to yaw further. The pilot then stated that he rolled off the throttle. The helicopter touched down with almost no forward speed, but the right landing skid collapsed, and the helicopter rolled over onto its right side. The pilot noted that he did not recall hearing the engine out beeper or the low rotor RPM horn, and he did not monitor engine or rotor RPM indications during the descent.
Post-Inspection Findings
A post-accident inspection of the airframe, followed by a detailed teardown of the engine and associated components, revealed no evidence of any mechanical failure or malfunction. The source of the sudden loss of altitude, yaw, and roll remains undetermined based on available evidence.