Accident Sequence
A witness stated that she heard the engine on the helicopter quit. Looking out her window, she watched the helicopter strike the ground. The aircraft bounced, struck the ground a second time, flipped over, and the tail separated. Subsequently, the helicopter burst into flames and exploded.
Engine Examination
Examination of the engine revealed that the PC air filter assembly was broken at the forward inlet side of the filter body. This break resulted in the loss of PC air pressure to the fuel control, which caused the engine power to reduce to flight idle. The PC filter housing broke due to an improper modification to the filter body.
Conclusion
The improper modification to the PC filter body led to the housing failure, loss of PC air pressure, and subsequent reduction of engine power to flight idle, preceding the ground impact and fire.