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The final report on the Whyalla Airlines Piper Chieftain VH-MZK accident on 31 May 2000, in which all eight occupants died, was released today by the Australian Transport Safety Bureau.

ATSB Executive Director, Kym Bills, made the following statement: "The VH-MZK accident occurred after mechanical failures involving both engines forced the pilot to ditch the aircraft in Spencer Gulf, about 26km from Whyalla, on a dark, cloudy and moonless night.

Based on careful analysis of the engine failures and recorded radar and audio data, it is likely that the left engine failed first as a result of a fatigue crack in the crankshaft. This was initiated about 50 flights before the accident flight due to the breakdown of a connecting rod bearing insert. The combined effects of high combustion gas pressures developed as a result of deposit-induced pre-ignition, and lowered bearing insert retention forces due to an 'anti-galling' lubricating compound used during engine assembly by the manufacturer, led to this breakdown.

Lean fuel practices used by the operator increased the likelihood of lead oxybromide deposit-induced pre-ignition but were within the engine operating limits set by the aircraft manufacturer.

It is likely that because of the increased power demanded of the right engine after the left engine failed, abnormal combustion (detonation) occurred and rapidly raised the temperature of the pistons and cylinder heads. As a result, a hole melted in the number 6 piston causing loss of engine power and erratic engine operation. The subsequent ditching involved great pilot skill.

The ATSB examined components from a further ten similar engines that have failed since January 2000 (including two engines from another manufacturer) in order to better understand the failure mechanisms. Combustion chamber deposits that may create lead oxybromide deposit-induced pre-ignition were found in these engines. The Bureau concluded that engines that were operated at lean fuel-air mixtures during climb, and towards best economy mixtures during cruise flight, were more likely to show signs of such deposit-induced pre-ignition than those engines operated at full rich mixture during climb and at best power mixture during cruise.

On 30 October 2000 ATSB released recommendations about the risks of detonation and lean running and in relation to the desirability of life jackets and other life-saving equipment on smaller passenger aircraft flying over water. Today, we release further recommendations to:

  • the US FAA in relation to engine deposits that may cause pre-ignition;
  • the US FAA and the engine manufacturer on the use of anti-galling compounds between connecting rod bearing inserts and housings during engine assembly;
  • CASA in relation to high power piston engine reliability more generally; and
  • CASA in relation to providing guidance to pilots on ditching.

While there were deficiencies with the Whyalla Airlines safety culture and gaps with the extent of the regulator's surveillance of the operator, neither were significant accident factors.

No-one should be blamed for this accident, but if the lessons from it are learned, both in Australia and internationally, some good will have come from the tragic deaths of eight people."

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Last update 01 April 2011