Accident Sequence
A commercial pilot conducting an on-demand air taxi flight in a turbine-powered helicopter was performing an aerial survey at approximately 100 feet above ground level when the engine-out annunciator sounded. The pilot initiated an autorotation and touched down in a small clearing with the collective pitch control fully raised to cushion the landing. Upon touchdown, the engine power surged unexpectedly, causing the helicopter to begin climbing. During the pilot's efforts to regain control, the main rotor blades struck several trees, severing the tail boom. The pilot then rolled the throttle to the off position, but the engine did not shut down; he subsequently pulled the emergency fuel shut-off.
Examination
Post-accident examination of the helicopter revealed that a bolt connecting the N2 governor input arm to an airframe-mounted bellcrank was missing. This bellcrank is linked to the collective control linkage; movement of the collective control adjusts engine power through this assembly. The bolt is normally secured with a castellated nut and a cotter pin. Company personnel later returned to the accident site and recovered the missing bolt and nut from the ground beneath the area where the engine access doors had been opened during an inspection before the helicopter was removed. Additionally, a cotter pin with one broken side was found, but it could not be determined whether it was the missing pin from the bolt.
Maintenance History
The most recent maintenance was a 100-hour inspection performed by company personnel 51.8 flight hours before the accident. Numerous company pilots had flown the helicopter prior to the accident, and each conducted a preflight inspection. On the day of the accident, the helicopter had accumulated about 2.5 hours of flight time before the event.