Incident Summary
A flight instructor and an instrument student were conducting an IFR cross-country flight. While descending from 11,000 feet to 5,000 feet, the oil annunciator light illuminated and the oil pressure gauge indicated no pressure. The engine began to run rough and vibrate, and then lost power. The crew declared an emergency and were vectored toward a nearby airport. The engine made "a loud squealing noise" before it shut down completely. Unable to reach the airport, they executed a forced landing on unsuitable terrain.
Engine Examination
Post-accident examination of the engines identified a breach in the crankcase above the No. 6 cylinder. The No. 6 connecting rod had separated from the crankshaft, and the connecting rod and crankshaft journal showed heat distress consistent with loss of lubrication. A fragment of a broken connecting rod bolt exhibited signs of ductile overload.
Further inspection revealed that the oil hose supplying pressure lubrication to the turbo bearing (part number 124F003-6GR0262, rated at 1,500 psi) was in contact with the exhaust system pipes. The heat shield was burned through at two locations, with evidence of chafing and heat distress. A pressure test of the hose produced air bubbles, indicating a breach.
Maintenance History
According to the engine maintenance logbook, two damaged oil lines had been removed and replaced the year prior due to overheating from the exhaust system.