BELMONT, MS, USA
N23PH
Bell 47G-4A (SOLOY)
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.
On September 19, 1996, about 1245 central daylight time, a Bell 47G-4A Soloy, collided with trees during an emergency descent, near Belmont, Mississippi. The helicopter was operated by Provine Helicopter Service, Inc. under the provisions of Title 14 CFR Part 137, and visual flight rules. Visual meteorological conditions prevailed. A flight plan was not filed for the aerial application flight. There were minor injuries to the commercial pilot, and the helicopter was substantially damaged. Origination of the flight was a remote operating site near Belmont, Mississippi, about 1242, on the same day. According to the pilot, he experienced increasing vibrations in the rudder pedals during successive spray runs. Subsequently, he lost yaw control as the helicopter began rotating, to the right, about the vertical axis. An autorotation was executed into a heavily wooded area. The FAA inspector who examined the helicopter and the operator indicated that there was extensive damage to the main rotor blades and fuselage, with virtually no damage to the tail rotor blades. Additionally, they reported that the aft universal joint for the tail rotor drive shaft exhibited little evidence of lubrication. The airworthiness inspector who examined the helicopter and its records reported that a 1200 hour inspection was completed on July 30, 1996, at an aircraft time of 9696.2 hours. The repair station operator that conducted the inspection stated that he used red lubricant to lubricate the bearings and the universal joint that failed. No red grease was found in the universal joint during its disassembly following the accident. The tail rotor drive shaft exhibited blue discoloration The manufacturer's helicopter maintenance manual recommends lubricating the tail rotor bearings and universal joint at 50 hour intervals. No log book entries were found to indicate that the helicopter had been lubricated in the 153.7 operating hours since the 1200 hour inspection.
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.
Source: NTSB Aviation Accident Database
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