At about 2010 Western Standard Time on 29th January 2010, a single engine Pilatus PC-12 aircraft, registered VH-NWO, was being operated on a night medical evacuation flight from Derby to Kununurra, Western Australia with four persons on board. The pilot reported that about 56 km after takeoff, as the aircraft was passing through flight level 180, the engine exhibited a number of problems before the pilot turned the aircraft back to the departure airport. The engine failed and the pilot glided the aircraft to land at Derby. There were no injuries. Subsequent inspection confirmed that the engine propeller reduction gearbox had seized.