Incident Overview
During a cross-country positioning flight, the helicopter's engine suffered a partial loss of power while in cruise flight. The pilot executed an autorotation to a field, which was rough and uneven. During the landing sequence, the helicopter's lower wire cutter dug into the uneven ground, causing the helicopter to rock forward. The skid support cross tubes buckled aft as a result. As the helicopter settled, a main rotor blade struck the left winglet of the horizontal stabilizer, and the tail boom was wrinkled.
Examination Findings
Examination of the engine revealed that the angular contact ball bearing on the power takeoff shaft had failed. The balls from the bearing had fallen into the gearbox oil sump, and one ball had lodged in the oil exit port, blocking the flow of oil out of the gearbox. Consequently, the gearbox filled with oil, the oil tank emptied, and power section components began to overheat due to lubricating oil starvation.
Maintenance History
Engine records provided evidence that during maintenance performed 28.7 hours prior to the engine failure, repair station personnel had removed, inspected, and reinstalled the failed bearing. Examination of the bearing provided evidence that it had been pressed apart and reassembled with the outer race reversed. The manufacturer authorizes no disassembly of the bearing. According to the manufacturer, with the outer race reversed, the bearing will immediately start to deteriorate when placed in service.