What happened
While cruising at 5,500 feet, the pilot detected the smell of burning oil. Shortly thereafter, the engine lost oil pressure, causing the propeller to enter high RPM and the tachometer to exceed the redline. A loud report was heard, followed by a total loss of engine power.
The pilot attempted a forced landing in rolling terrain; however, the aircraft struck a tree and a fence during the maneuver. There were no fatalities or injuries reported.
The investigation
An examination of the engine revealed that the number 6 connecting rod cap had failed. This failure led to a progressive and massive internal engine failure caused by oil starvation.
Investigators determined that the oil starvation originated from a broken oil supply hose that runs from the oil cooler to the accessory drive section of the engine. The hose, which was 12 years old at the time of the accident, had accumulated 802 hours of use since its installation in 1978. While the recommended replacement interval for this hose is 1,000 hours, the component was difficult to inspect because it is encased in a fire insulation sleeve. This sleeve prevents the hose from being readily seen without disconnecting it from the aircraft and withdrawing it from the insulation.