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The ATSB has found that a Cessna 208 engine failure and forced landing onto a lake in a remote part of south-western Tasmania last year was due to a previous generator failure, has praised the pilots actions in landing the aircraft and ensuring passenger safety, and has made a number of safety recommendations to prevent a similar failure.

The Australian Transport Safety Bureaus final investigation report states that the aircraft, a single engine Cessna 208 floatplane was being operated on a commercial scenic flight over rugged terrain with a pilot and 10 passengers. The occupants were fortunate to escape unharmed, due to the pilots prompt actions in diverting to Lake Burbury when an engine chip-detector warning light came on. Within minutes of the warning light illuminating, the engine failed completely and the pilot was able to conduct a forced landing onto the lake. The aircraft ended up on a mud bank on the edge of the lake and the occupants were able to walk away unharmed.

A previous generator failure led to electrical discharge damage (EDD) to the engine, resulting in its failure in-flight. EDD is a known problem with the Pratt and Whitney Canada PT-6 series turbo-prop engines fitted to this aircraft type. The ATSB has investigated similar events in Australia previously and the ATSB report cites 43 similar events reported worldwide since 1992. Some of these events have also been investigated by the US National Transportation Safety Board.

As a result of the ATSB investigation into this serious incident, a number of safety actions have been implemented by the aircraft and engine manufacturers as well as Australias Civil Aviation Safety Authority (CASA). CASA has advised the ATSB that it will issue mandatory aircraft maintenance instructions and Airworthiness Bulletins to reduce the possibility of EDD occurring and will highlight the issue to the Australian aviation industry through its Flight Safety Australia magazine.

While the safety actions of all parties are to be commended, the ATSB remains concerned that there remain safety issues that need to be addressed to eliminate the possibility of EDD events leading to engine failures of this engine type. The ATSB final report therefore contains a number of safety recommendations to the aircraft and engine manufacturer, the Canadian and US airworthiness authorities, Transport Canada and the Federal Aviation Administration and CASA.

Copies of the report can be downloaded from the ATSBs internet site at www.atsb.gov.au

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Last update 01 April 2011