EMMA KELLY / PERTH
The Australian Transport Safety Bureau (ATSB) is standing by the original conclusions of its inquiry into the May 2000 fatal crash of a Whyalla Airlines Piper Navajo Chieftain after a second investigation. This followed new evidence about possible manufacturing defects in the aircraft's Textron Lycoming T10-540-52B engines and came after the bureau's original conclusions and investigation were criticised and rejected by the South Australian coroner during a public inquest into the crash (Flight International, 29 July-4 August).
The aircraft crashed near Whyalla, South Australia, killing the pilot and seven passengers, after a double engine failure.
The ATSB originally concluded that the left engine failed first due to a fractured crankshaft caused by fatigue, followed by the failure of the right engine after a holed number six piston due to melting of the piston material. The latter was attributed to the pilot increasing the engine power settings on the right engine, after failure of the left engine, to an inappropriate extent.
In contrast, the South Australian coroner concluded that the left and right engines had failed independently. The coroner said that the right engine overheated and was damaged during the climb, while the left engine subsequently independently failed because of fatigue cracking initiated by a sub-surface manufacturing defect.
The ATSB has subsequently conducted detailed examination of the crankshaft material and the fracture area and found no irregularity that could have initiated the fatigue fracture under normal operating conditions. The bureau believes the fatigue crack in the left engine initiated about 50 flights before the accident due to a thermal crack caused by localised surface heating when a bearing insert failed to operate as designed. The holing of the right engine was due to detonation in response to the left engine failure, it says.
Source: Flight International