PC12, en-route, near Derby Western Australia, 2010

PC12, en-route, near Derby Western Australia, 2010

Summary

On 29 January 2010, a Pilatus PC-12/45 being operated on an aerial work basis on a Medevac flight from Derby to Kununurra Western Australia and climbing through FL180 in night VMC experienced signs of engine malfunction and initiated an air turnback during which the engine failed completely. The subsequent 6nm glide descent and approach culminated in a successful landing with the aircraft undamaged and all four occupants unhurt.

Description

On 29 January 2010, a Pilatus PC-12/45 being operated on an aerial work basis on a Medevac flight from Derby to Kununurra Western Australia and climbing through FL180 in night Visual Meteorological Conditions (VMC) experienced signs of engine malfunction and initiated an air turnback during which the engine failed completely. The subsequent 6nm glide descent and approach culminated in a successful landing with the aircraft undamaged and all four occupants unhurt.

Investigation

An Investigation was carried out by the Australian Transport Safety Bureau (ATSB). An inspection confirmed that the engine propeller reduction gearbox had seized. Further investigation established that four of the six first-stage bolts on the propeller reduction gearbox had failed due to fatigue cracking at the head to shank fillet radius.

Figure reproduced from the Official Report showing the first stage reduction assembly and the location of the failed bolts

It can be seen from the illustration that, in addition to the six carrier bolts, the splined adapter was aligned and held in position by three locator pins adjacent to the carrier bolts. Further examination of the four failed bolts confirmed the mode of failure had been reverse bending fatigue below the head of each one.

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