On August 8, 1986, a Bell 47G-4A (registration N1185W) was involved in an aviation accident near Shafter, CA. Investigators recorded the probable cause as: Failure of the forward coupling tail rotor drive shaft due to extreme high temperature distress resulting from a lack of lubrication. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter's forward coupling tail rotor drive shaft failed shortly after takeoff during an agricultural aerial application operation. The pilot attempted an autorotation but the helicopter collided with the ground and rolled over. Examination found the coupling failed due to lack of lubrication.
Accident Details
Shortly after departing the loading rig, while en route to an agricultural aerial application operation, the forward coupling tail rotor drive shaft of the helicopter failed. At the time, the helicopter was approximately 10 feet above ground level and about 100 feet west of the loading rig. The pilot attempted an immediate autorotation; however, the helicopter collided with the ground and rolled over.
Examination Findings
Examination of the wreckage disclosed that the coupling sustained extreme high temperature distress due to a lack of lubrication. This condition led to the failure of the tail rotor drive shaft.
Maintenance History
The helicopter had flown 178 hours since the last annual/100-hour inspection. A 100-hour inspection is required for this type of operation. The investigation did not specify whether the required inspection had been conducted within the appropriate timeframe.
Probable cause
Failure of the forward coupling tail rotor drive shaft due to extreme high temperature distress resulting from a lack of lubrication.