On August 4, 1988, a Bell UH-1E (registration N151LC) was involved in an aviation accident near North Bend, OR. Investigators recorded the probable cause as: Failure of the tail rotor drive input gear due to fatigue. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a logging operation, the pilot noted a transmission malfunction and performed an autorotative landing on unprepared terrain, resulting in damage. Investigation revealed fatigue failure of the tail rotor drive input gear.
Accident Summary
During a logging operation, the pilot of helicopter N151LC observed an apparent transmission malfunction. Subsequently, the pilot executed an autorotative landing on unprepared terrain. The helicopter sustained damage during the landing.
Investigation Findings
An investigation into the accident determined that the tail rotor drive input gear within the 42-degree gearbox had failed due to fatigue. The helicopter, N151LC, was a military surplus aircraft. The gearbox had been overhauled on June 15, 1987. According to the operator's records, the gearbox had accumulated 373 hours of service since the overhaul.
Probable cause
Failure of the tail rotor drive input gear due to fatigue.