Accident Sequence
A helicopter was performing a seismic survey operation at an altitude of 200 to 250 feet above ground level (AGL) and an airspeed of 40 knots. During the flight, the engine's automatic re-ignition system caution light illuminated, immediately followed by a loss of main rotor rpm. The pilot attempted to perform an autorotation but was unsuccessful, and the aircraft subsequently impacted the ground.
Postaccident Examination
A postaccident examination of the turboshaft engine revealed that the PC line 'B' nut, located between the fuel control unit (FCU) and the power turbine governor (PTG), was not connected at the FCU. This disconnection resulted in a loss of engine pneumatic pressure, leading to the power loss.
Maintenance History
According to aircraft maintenance records, the turbine section of the engine had been removed by company maintenance personnel and replaced with a rental turbine. During the removal and replacement of the engine's turbine section, the PC line and various pneumatic and fuel system lines had been disconnected. The helicopter had accumulated 6.1 flight hours since the turbine replacement.