The PA31-350 aircraft was in cruise flight, at 8,000 ft, when the flight crew noticed that the propellers went out of synchronisation. Adjustments were made to correct the problem but were unsuccessful. Following right engine RPM fluctuations, the crew shut the engine down, feathered the propeller and conducted a single engine landing.

During the subsequent disassembly of the engine, the crankshaft was noted to have fractured at the number-6 connecting rod journal.

The engine components were sent to the ATSB for further technical analysis. Analysis of the fracture indicated that fatigue cracking had initiated below the surface of the journal, associated with a discontinuity in the nitrided surface zone, at the transition from the journal to the forward fillet radius. The number-6 connecting rod bearing inserts had been destroyed during operation; the remnants included flattened fragments of steel backing material. In addition, fatigue crack growth had commenced at the centre of the connecting rod cap, most probably after the bearing inserts had failed.

Because of the small amount of bearing debris available for testing, the reason the number-6 bearing inserts failed could not be determined.

This engine failure is one of a number of events being used in a detailed safety study of failures to high powered piston engines. On completion, the results will be available on the ATSB website www.atsb.gov.au or from the Bureau on request.