On June 11, 1995, a Cessna T210N (registration N5436Y) was involved in an aviation accident near Fall River Mill, CA. Investigators recorded the probable cause as: The No. 2 lower connecting rod bolt fractured due to being undertorqued during the last engine overhaul, which had occurred 509 flight hours prior. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
After leveling at cruise, an engine began running rough, with metallic sounds, oil pressure drop, and oil on windscreen. A forced landing in a lava field resulted in the aircraft nosing over. Investigation found an undertorqued connecting rod bolt.
Accident Sequence
The aircraft had just leveled off at cruise altitude when the engine started running roughly. A 2-inch reduction in manifold pressure produced a metallic sound. An additional 2-inch reduction resulted in a louder metallic noise. Subsequently, the manifold pressure dropped to 20 inches, oil pressure fell to zero, and oil began to splatter on the windscreen.
Forced Landing
The pilot executed a forced landing in a lava field surrounded by trees. After touchdown, the aircraft slid and nosed over onto its back.
Postaccident Inspection
Examination of the engine revealed that the No. 2 lower connecting rod bolt had fractured. Measurements performed by the engine manufacturer indicated that the rod bolt had been undertorqued. The engine had last been overhauled 509 flight hours prior to the accident.
Probable cause
The No. 2 lower connecting rod bolt fractured due to being undertorqued during the last engine overhaul, which had occurred 509 flight hours prior.