NTSB Identification: SEA01LA121.
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Accident occurred Tuesday, June 26, 2001 in Mullan, ID
Probable Cause Approval Date: 02/25/2003
Aircraft: Kaman HH-43B, registration: N556D
Injuries: 1 Minor.

NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot was preparing to lift a load of logs from a 150-foot hover in the Kaman HH-43B helicopter when a total loss of power occurred. He transitioned into an autorotation colliding with the steeply sloped, tree covered terrain. A partial disassembly of the ex-military Lycoming T53-L-13B turboshaft engine revealed that the 1st stage gas producer turbine rotor sealing disc was fractured and had broken into three approximately equal sized segments. Metallurgical examination of the disc fragments revealed fatigue cracks through three of the six cooling holes, and examination of the fracture faces for all three cooling holes by scanning electron microscope revealed multiple fatigue striations at each fracture face.

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

The development of multiple fatigue cracks which ultimately resulted in the fracture of the 1st stage gas producer turbine rotor sealing disc. Factors contributing to the accident were mountainous/hilly and unsuitable terrain conditions.

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