On June 12, 1986, a Bell 47G-2 (registration N11VH) was involved in an aviation accident near Zillah, WA. Investigators recorded the probable cause as: The most likely cause of the overheating was due to a deteriorated bearing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced total power loss and oil pressure loss while en route to a spray area. Autorotation attempt resulted in left skid catching a metal shed roof, causing crash and rollover. Investigation found connecting rod bolt failure due to fatigue and overheating from deteriorated bearing.
Incident Overview
While en route to a local spray area, the helicopter suffered a total loss of engine power accompanied by a loss of oil pressure. At the time, the aircraft was approximately 200 feet above ground level over a pear orchard. The pilot initiated an autorotation and attempted to land on a nearby road.
Accident Sequence
During the autorotation, the helicopter's left skid made contact with the rooftop of a metal shed. The helicopter then crashed through the roof of the shed and rolled over onto its side. The aircraft came to rest on its side.
Investigation Findings
Post-accident investigation revealed that the number three cylinder rod bolt had failed. A metallurgical examination determined that the number three cylinder connecting rod cap failed due to overstress forces caused by excessive heating of the rod and cap. The failure of the number three cylinder connecting rod bolt was attributed to fatigue cracking. The most likely cause of the overheating was a deteriorated bearing.
Probable cause
The most likely cause of the overheating was due to a deteriorated bearing.