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Tail Rotor Drive Shaft Failure During Agricultural Flight (N1185W)

Shafter, CA, US

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.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-07-04Data APIEditorial standards

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.
Maintenance error

Frequently asked questions

What happened in the 8 Aug 1986 Bell 47G-4A accident near Shafter, CA?

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.

What aircraft was involved and where did it happen?

The accident on 8 Aug 1986 involved a Bell 47G-4A, registration N1185W, at Shafter, CA.

What was the probable cause of the accident?

Failure of the forward coupling tail rotor drive shaft due to extreme high temperature distress resulting from a lack of lubrication.

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001213X34502. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.