The pilot reported that while in cruise flight over water, the
C182 aircraft was subjected to a strong downdraft. The pilot
immediately reduced engine power to slow the aircraft in
anticipation of further turbulence. Having established the desired
airspeed, the pilot attempted to re-apply power but the engine did
not respond. He selected carburettor heat and attempted several
times to start the engine.
As there was no suitable landing area on nearby Huon Island, the
pilot ditched the aircraft 1 km from the mainland shore. Three of
the four occupants exited the aircraft unassisted; the fourth had
to be pulled free by the pilot. All then made their way to the
shoreline.
Subsequent salvage attempts were unable to locate the wreckage.
Consequently, to assess the airworthiness of the aircraft, the
investigation could examine only the aircraft documentation. No
deficiencies that might have contributed to the accident were
identified.
Information provided by the Bureau of Meteorology indicated that
atmospheric conditions at the time of the engine failure were
conducive to the formation of moderate to severe carburettor icing.
The formation of ice in the carburettor venturi can result in
partial or complete loss of power. Contamination of the fuel system
was also considered. However, the aircraft operator said that the
aircraft had not been fuelled from known contaminated batches.
The investigation could not determine why the engine failed.
However, it is possible that carburettor icing formed after the
pilot reduced power in response to the turbulent conditions.