What happened
During an instrument flight rules (IFR) cross-country flight, a flight instructor and an instrument student were descending from 11,000 feet to 5,000 feet when the oil annunciator light illuminated. Simultaneously, the oil pressure gauge indicated zero pressure. The engine began to vibrate and run roughly before losing power completely. During the failure, the engine produced a loud squealing noise. After declaring an emergency and being vectored toward a nearby airport, the crew was unable to reach the airfield and performed a forced landing on unsuitable terrain. There were no fatalities reported.
The investigation
Post-accident examination of the engine revealed a breach in the crankcase located above the number 6 cylinder. Investigators determined that the number 6 connecting rod had separated from the crankshaft. Both the connecting rod and the crankshaft journal showed evidence of heat distress resulting from a loss of lubrication. Additionally, a fragment of a broken connecting rod bolt exhibited signs of ductile overload.
Further inspection found that the oil hose responsible for supplying pressure lubrication to the turbo bearing was making contact with the exhaust system pipes. The heat shield protecting this area had been burned through at two locations, showing evidence of chafing and heat distress. A pressure test performed on the hose revealed the presence of air bubbles. Maintenance records indicated that two other damaged oil lines had been replaced the previous year due to overheating caused by the exhaust system.