Forced/precautionary landing involving a Pitts S-1, N540KB, 7 km south-west of Mooroopna, Victoria, on 24 November 1994

The owner/pilot advised that he was practising an aerobatic sequence for a future airshow when the engine suddenly suffered a partial power loss. At the time the aircraft was vertical. The pilot pushed over to level flight at about 1000 ft AGL and 80 kts. Then the engine stopped completely. He performed a forced landing in a nearby paddock. The aircraft touched down at approximately 115 kts. During the landing roll the aircraft flipped twice onto its back before coming to rest upright but nose down.

Subsequently an engineer discovered that the crankshaft thrust bearing had seized. The pilot and the engineer believe that, during aerobatic manoeuvres, the oil pickup pipe had been exposed and sucked air, thereby starving the thrust bearing of oil.

This particular aircraft has a more powerful engine installed than the standard Pitts. The additional horsepower enables very high-performance aerobatics.

The owner/pilot, his engineer, the manufacturer and the CAA are involved in achieving an improved oil supply to the thrust bearing before the engine is returned to service.

Significant Factors

The following factors were considered relevant to the development of the accident:

1. The crankshaft thrust bearing was inadequately lubricated during aerobatic manoeuvres.

2. The crankshaft thrust bearing seized and stopped the engine.

3. During the landing roll, the aircraft encountered an undulation and overturned.