On September 18, 1986, a Hiller UH-12E (registration N688SB) operated by West Farm Air was involved in an aviation accident near Lemoore, CA. Investigators recorded the probable cause as: The number 3 connecting rod bolts failed, and the remaining connecting rod bolts had torque values approximately 50% less than required. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter rolled onto its side during an autorotation after the pilot heard a loud pop and saw an engine fire, losing cyclic control. Investigation found connecting rod bolt failure and insufficient torque values.
Incident Overview
The pilot of a helicopter reported that while returning to the loading area after spraying a field, he heard a loud pop emanating from the engine compartment. Shortly thereafter, he observed a fire in the engine compartment and lost forward and aft control of the helicopter. The pilot immediately executed an autorotation. The helicopter rolled over onto its side on touchdown.
Post-Accident Investigation
Post-accident examination of the engine disclosed that the number 3 connecting rod bolts failed. Further examination revealed that the remaining connecting rod bolts had torque values approximately 50% less than the required values.
Probable cause
The number 3 connecting rod bolts failed, and the remaining connecting rod bolts had torque values approximately 50% less than required.
What happened in the 18 Sept 1986 Hiller UH-12E accident near Lemoore, CA?
A helicopter rolled onto its side during an autorotation after the pilot heard a loud pop and saw an engine fire, losing cyclic control. Investigation found connecting rod bolt failure and insufficient torque values.
What aircraft was involved and where did it happen?
The accident on 18 Sept 1986 involved a Hiller UH-12E, registration N688SB, operated by West Farm Air, at Lemoore, CA.
What was the probable cause of the accident?
The number 3 connecting rod bolts failed, and the remaining connecting rod bolts had torque values approximately 50% less than required.
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