Incident Overview
A test flight was conducted following the installation of a fuel control/governor on an aircraft. During the flight, the engine unexpectedly accelerated to maximum power and could not be controlled by the pilot. The pilot subsequently secured the engine and initiated an autorotation.
Touchdown and Damage
During the landing sequence of the autorotation, the main rotor blades made contact with the tail boom. This contact severed the tail rotor drive shaft, resulting in further damage to the aircraft.
Examination Findings
A post-incident examination of the fuel control/governor was performed. Investigators discovered a piece of abrasive paper lodged within the reset shaft housing. According to the examination report, the presence of this foreign object would cause a loss of governor control to the high side, explaining the uncontrolled engine acceleration.
Conclusion
The incident was investigated, and the physical evidence pointed to the abrasive paper as the cause of the governor malfunction. No other contributing factors were identified in the source material.