FTW01LA214

The helicopter was on approach to an offshore platform, turning from base to final at 300 feet, when the pilot heard the low rotor rpm audio warning, and then noticed that the low rotor rpm warning light was illuminated. He initiated an autorotation and observed that the rotor rpm needle had dropped to zero. The pilot stated that as the helicopter was descending, he noticed feedback in the flight controls and decided that a precautionary landing was necessary. Subsequently, the pilot landed the helicopter in the water and shut down the engine. During the main rotor coast down, the tail rotor contacted a five foot wave, resulting in separation of the tail rotor drive shaft. The internal splines of the shaft and sleeve assembly of the rotor tachometer generator (part number 206-076-373-001) were found to be worn and not engaging. The failure of the rotor tachometer generator splines resulted in a loss of hydraulic pressure to the helicopter flight controls, since the hydraulic pump is driven by the rotor tachometer generator.

On September 26, 2001, at 1239 central daylight time, a Bell 206L-1 helicopter, N1067D, was substantially damaged when its tail rotor contacted water while standing during main rotor coast down, following a precautionary landing in the Gulf of Mexico. The helicopter was owned and operated by Air Logistics LLC, of New Iberia, Louisiana. The commercial pilot and his two passengers were not injured. Visual meteorological conditions prevailed and a company visual flight rules flight plan was filed for the 14 Code of Federal Regulations Part 135 on-demand air taxi flight. The flight originated from Creole, Louisiana, at 1222, and was destined for West Cameron 168, an off-shore platform in the Gulf of Mexico.

According to the pilot, the helicopter was approximately 100 feet from the destination platform, turning from base to final at 300 feet, when he heard the low rotor rpm audio warning, and then noticed that the low rotor rpm light was illuminated. He initiated an autorotation and observed that the rotor needle had dropped to zero. The pilot stated that as the helicopter was descending, he noticed "feedback" in the flight controls and "decided that a precautionary landing was necessary." Subsequently, the pilot landed the helicopter in the water and shut down the engine. According to the operator, "the #5 tail rotor drive shaft was broken during rotor coast down due to the tail rotor contacting a 5-foot wave on shut down." The pilot and two passengers were then rescued by emergency crews. Subsequently, the helicopter,. which remained afloat, was recovered and transported to the operator's maintenance facility for further examination.

An FAA inspector and representatives from Air Logistics LLC examined the helicopter. They confirmed that the tail rotor drive shaft was separated. They discovered that the internal splines on the shaft and sleeve assembly of the Rotor Tachometer Generator (Globe Industries part number 206-076-373-001) were worn and not engaging. According to the FAA inspector, the output shaft from the main transmission oil pump drives the rotor tachometer generator, and the hydraulic pump is driven from the rotor tachometer generator. Therefore, if the rotor tachometer generator fails, the hydraulic pump also fails. The rotor tachometer generator is not time life limited, nor is there an inspection required for the unit.