A Pilatus PC-12 propeller gearbox failure in Australia has revealed a faulty manufacturing process, leading to service bulletins being sent to affected operators, according to an Australian Transport Safety Bureau investigation.

On 29 January 2010, a single-engine Pilatus PC-12 aircraft (VH-NWO) took off for a night medical evacuation flight from Derby to Kununurra, Western Australia, with four people on board.

The pilot reported that after about 56km (30nm), as the aircraft was passing through flight level 180, the engine began to develop problems. The pilot then turned back for the departure airport.

The engine subsequently failed and the pilot glided the aircraft to land safely at Derby. There were no injuries. A later inspection confirmed the engine propeller reduction gearbox had seized.

The investigation found that four of the six first-stage reduction gearbox retaining bolts on the Pratt & Whitney Canada PT6A-67B had failed because of fatigue.

A further investigation by the engine manufacturer determined that a quantity of first-stage reduction assembly carrier bolts had missed an essential part of the manufacturing process that ensures proper resilience.

The engine manufacturer then issued a number of bulletins identifying the affected gearboxes and specifying compliance times for the removal and replacement of suspect carrier bolts.

Source: Flight International