Incident Overview
A single-engine charter aircraft departed Broome for Koolan Island, Western Australia, on a routine flight. At approximately 0645 Western Standard Time, while cruising at 9,500 feet, the pilot observed a drop in the engine torque indication accompanied by a corresponding decrease in engine oil pressure. Advancing the power lever did not arrest the decline; other engine parameters remained normal. The pilot reported a perceived loss of power and decided to divert to the nearest airstrip at Beagle Bay.
Emergency Landing
During the diversion, the low oil pressure warning light illuminated. The pilot shut down the engine and prepared for an emergency landing. On final approach, the aircraft was too high and too fast. Touchdown occurred about midway along the runway, and the aircraft overran the end by approximately 200 metres, striking a mound of dirt before coming to rest inverted.
Injuries and Damage
The pilot, the only person on board, sustained minor injuries. Post-accident examination revealed that the engine, left main landing gear, and nose gear had separated from the airframe during the accident sequence. A significant amount of oil was present on the underside of the aircraft, indicating an in-flight oil leak from the engine.
Engine Examination
The engine was removed from the site as an assembly by a third party, the propeller was detached, and the engine was shipped to an overhaul facility. A disassembly and examination were conducted under the supervision of the Australian Transport Safety Bureau (ATSB).
Investigation Findings
The investigation concluded that the engine had suffered a substantial in-flight oil leak, necessitating the shutdown and diversion. Accident damage to the engine in the area of the apparent leak precluded a definitive determination of the leak source, but the oil tube was identified as the most likely origin. Examination of the oil tube attachment lug fracture surfaces was inconclusive; however, evidence from similar failures indicated that vibratory loading could cause the lugs to fracture in the manner observed on the oil tube fitted to VH-NTQ. No evidence was found of a compressor turbine or power turbine blade failure, an incorrectly fitted engine mount, or a pre-existing defect that would have caused a reduction in actual engine torque.