Loss of Engine Power
While cruising at approximately 6,000 feet mean sea level, one cylinder exhibited a loss of exhaust gas and cylinder head temperature. Subsequently, the crew felt a rapidly intensifying vibration, oil spread across the front windscreen, and all engine power ceased.
Forced Landing and Impact
During the landing flare, the airplane collided with an oak tree, a fence, and a rock outcrop. The impact caused the engine to separate from the firewall. Further inspection revealed that the number 6 cylinder had broken away from the engine case.
Engine Examination
A teardown of the engine showed that the case halves had oil residue at their union. The torque values on all engine through-bolts, combined with fretting marks at the base of the number 6 cylinder, indicated that the cylinder bolts had been inadequately torqued during installation.
Maintenance History
An interview with the mechanic who replaced the six cylinders in May 2005 revealed that he had torqued the nuts to approximately 500 inch-pounds. According to TCM's 1989 maintenance manual, the required torque for the through-bolts was 690 to 710 inch-pounds. By 1996, TCM had issued service bulletin 96-7, which increased the torque requirement to between 790 and 810 inch-pounds.