NTSB Identification: DEN99LA040.
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Accident occurred Monday, February 15, 1999 in BAGGS, WY
Probable Cause Approval Date: 05/08/2001
Aircraft: Hughes 369D, registration: CGDCM
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The helicopter was conducting a seismic survey operation at 200 to 250 feet agl at 40 knots when the engine's automatic re-ignition system caution light illuminated, followed by an immediate loss of main rotor rpm. The pilot unsuccessfully attempted to perform an autorotation, and the aircraft impacted the ground. A postaccident examination of the turboshaft engine was performed, revealing that the PC line 'B' nut between the fuel control unit (FCU) and the power turbine governor (PTG) was not connected at the FCU, resulting in a loss of engine pneumatic pressure. According to aircraft maintenance records, the turbine section of the engine was removed by company maintenance and replaced with a rental turbine. The PC line and various pneumatic and fuel system lines had been removed to facilitate removal and replacement of the engine's turbine section. The helicopter had flown 6.1 hours since the turbine was replaced.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A hard landing resulting from rotor rpm decay. Factors were the improper replacement of the turbine by company maintenance personnel resulting in the PC line nut becoming loose, and the pilot operating outside the normal height/velocity curve.

Full narrative available

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