Grant County Regional/Ogilvie Field Airport: John Day, Oregon

Grant County Regional/Ogilvie Field Airport Today:

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. (Dayville)