NTSB Identification: SEA06LA065.
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Accident occurred Sunday, March 12, 2006 in Dexter, OR
Probable Cause Approval Date: 03/26/2007
Aircraft: Kaman K-1200, registration: N133KA
Injuries: 1 Minor.

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

While approaching the collection point with a load of logs, the helicopter's power turbine and rotor system experienced a steady-state overspeed due to the failure of the splines on the shaft that provides turbine speed input to the turbine governor. Without this input, the governor erroneously sensed a turbine underspeed, and therefore provided fuel in excess of that required to maintain the correct speed. The splines failed due to a significant reduction in the flow of lubricating oil resulting from the partial blockage of an oil filter outflow orifice. The outflow orifice became partially blocked because the oil filter screen was aligned in its housing in a manner that allowed some contaminants to bypass it. Although the Kaman K-1200 Flight Manual contains an emergency procedure that allows for the pilot to take manual (non-governed) control of the fuel input to the engine in the event of a governor failure, the pilot did not perform the procedure because he was not able to correctly identify the cause of the sequence of events.

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

The pilot's failure to identify the overspeed of the helicopter's main rotors due to a turbine governor malfunction, and his failure to take the appropriate actions described in the Flight Manual's emergency procedures section. Factors include the malfunction (partial bypass) of a lubricating system filter screen, which led to the partial blockage of an oil supply orifice, resulting in the failure of the splines on the power turbine governor speed input shaft, and ultimately to the loss of the governor's ability to correctly control fuel input to the engine. Additional factors include no suitable landing terrain and tree stumps in the area the pilot elected to land in.

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