NTSB Identification: SEA06FA067.
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Accident occurred Friday, March 17, 2006 in Dayville, OR
Probable Cause Approval Date: 05/29/2007
Aircraft: Kaman K-1200, registration: N263KA
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The helicopter experienced a total loss of engine power while hovering out of ground effect during a long-line logging operation. Witnesses observed the helicopter descend vertically with the rotors visibly slowing down, nose over to an inverted position, impact the ground inverted, and roll onto its left side. Initial examination of the engine revealed that when the power turbine was rotated, the engine output adapter attached to the reduction gearbox did not rotate, indicating a mechanical disconnect within the engine. Disassembly of the engine revealed severe damage to the sun gear shaft, which coupled the power turbine to the reduction gear box. Further disassembly and materials analysis disclosed an assembly error of one of the three aft planetary gear shaft roller bearings in the reduction gear box and improper crimping of the lockcup on the N1 seal and nut assembly. These two errors resulted in misalignment in the planetary gear train leading to high tooth loading in the sun gear shaft, which resulted in stripping and separation of gear teeth and loss of transmitted torque through the reduction gear box. Examination of maintenance records indicated that the bearing assembly error occurred during an overhaul of the reduction gear box by a certified repair station 822.8 operating hours before the accident. The improper crimping of the lockcup occurred during a repair by the same certified repair station performed 350.2 operating hours before the accident.

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

The improper overhaul of the reduction gear box assembly and improper installation of the N1 seal and nut assembly lockcup by maintenance personnel, which resulted in failure of the reduction gear box and a total loss of engine power. A contributing factor was the pilot's failure to maintain adequate rotor rpm following the power loss, which resulted in an uncontrolled descent to ground impact.

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