HISTORY OF FLIGHT On October 7, 2000, about 1740 Pacific daylight time, a McDonnell Douglas (MD) 369E helicopter, N819CE, was substantially damaged during an emergency landing in mountainous terrain near Kernville, California. The helicopter was operated by Southern California Edison under the provisions of 14 CFR Part 91. The airline transport rated pilot received minor injuries. Visual meteorological conditions prevailed for the positioning flight, and a company flight plan was filed. The flight originated at Big Creek, California, about 1645, and was destined for Ontario, California. The helicopter was being repositioned to the Edison maintenance facility at Ontario for a 300-hour inspection. The pilot stated that he was descending from 7,500 feet mean sea level (msl) with an indicated airspeed of 125 knots. The first indication of trouble was a loud snap sound from the rear of the helicopter, followed by a violent airframe vibration. He noted that the only warning panel light that was illuminated was the generator fail light. He reported that there were no unusual vibrations in any of the controls. The pilot made a right turn to land on the best available terrain. As the turn was completed, tail rotor effectiveness was lost, and the helicopter began a series of rapid clockwise spins. The helicopter spun at least three times before impact. PERSONNEL INFORMATION Review of the Federal Aviation Administration (FAA) Airman Certification Records disclosed the pilot held an airline transport certificate with ratings for airplane single and multiengine land and rotorcraft/helicopters. He is instrument rated for airplanes and helicopters. The pilot's most recent first-class medical certificate was issued on September 18, 2000, with the limitation to have glasses available for near vision. According to flight department records, at the time of the accident the pilot had accumulated 24,424 total flight hours, with 9,647 hours in the accident make and model. In the 90 days prior to the accident, he had accumulated 176 flight hours. AIRCRAFT INFORMATION The most recent 100-hour inspection per the manufacturer's program occurred 93 hours prior to the accident. The helicopter had accumulated a total flight time of 7,772 hours, and was inbound to Ontario for a 300-hour inspection. WRECKAGE AND IMPACT INFORMATION The Safety Board, with the parties to the investigation, viewed the wreckage at the operator's facility in Ontario. The tail boom was separated at FS258.0 by an angular slash with sheet metal skin displaced in the direction of main rotor rotation. The separation point is within the disk radius of the main rotor. The tail rotor drive shaft remained attached at the main transmission via the forward Kamatics coupling and at the tail rotor gearbox via the aft Kamatics coupling. The drive shaft evidenced two fractures, one at FS 258.0 and the second at 8 inches forward of the aft Kamatics coupling. The forward (FS258.0) fracture was accompanied by significant bending of the drive shaft. The drive shaft immediately aft of the rear fracture was torsionally twisted. Leading edge tail rotor blade damage was observed to both blades, with red and blue color and material transfers evident. Examination of the tail rotor blade leading edges by Fourier Transform Infrared (FTIR) Spectrometer of the accumulation revealed the material to be of a cellophane base. The pilot reported that prior to departure from Big Creek, he placed a red and blue checkered shirt contained in a plastic bag on the rear seat with other personal baggage. He speculated that during his descent from 7,500 feet msl he had experienced some turbulence, and the left rear door may have popped open. Neither the bag nor the shirt was recovered at the accident site. ADDITIONAL INFORMATION The Safety Board did not take possession of the wreckage.