Accident Overview
A commercial pilot, who also served as a mechanic, conducted a maintenance flight in a helicopter. Following takeoff, the pilot performed four 90-degree pedal turns without any anomalies. The helicopter was then climbed to 500 feet, where the pilot initiated a left turn while lowering the collective. The nose was lowered to gain airspeed, and a simulated autorotation was entered.
Flight Maneuver and Control Failure
As the pilot increased collective input, the helicopter continued to descend and the collective appeared ineffective. Despite moving the collective to the full up position, the helicopter continued to sink and impacted the ground. The helicopter bounced and subsequently rolled over into a ditch.
Post-Accident Examination
An FAA inspector examined the helicopter and found that the left collective torque tube was fractured at its welded attachment point to the base. The weld fracture surface exhibited rust, but further examination indicated an overstress fracture. Additionally, the left collective torque tube interfered with the left seat and could not be extended to the full up position. No previous anomalies with collective movement had been reported prior to the accident flight. No mechanical deficiencies or belt slippage were observed with the belts.
Conclusion
The examination revealed structural issues with the collective torque tube, but no specific cause was assigned in the source.