NTSB Identification: ATL96LA129.
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Accident occurred Thursday, September 19, 1996 in BELMONT, MS
Probable Cause Approval Date: 07/28/1997
Aircraft: Bell 47G-4A (SOLOY), registration: N23PH
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During an aerial application operation, the pilot was making east and west swath runs. He reported that he had dispensed about half of his load, when he noted a vibration in the tail rotor pedals during a turn-around maneuver. He conducted three more swath runs with the vibration becoming progressively worse during each turn-around. Subsequently, during the fourth turn-around, the tail rotor drive was lost when the tail rotor drive shaft aft universal joint failed. Examination of the universal joint revealed a lack of lubricant, and the tail rotor drive shaft was discolored blue. There was no log book entry to indicate that the universal joint had been lubricated in the 150 plus hours of operation since the last inspection. The manufacturer's recommended maintenance practices included lubrication of the universal joint after each 50 hours of operation.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

failure of the aft universal joint of the tail rotor drive shaft, due to inadequate lubrication by company maintenance personnel. A factor relating to the accident was the pilot's delay in discontinuing the flight after noting a progressively worse tail rotor drive vibration.

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