HISTORY OF FLIGHT On August 28, 2005, at 0915 central daylight time, an experimental amateur-built Allensworth Baby Belle helicopter, N9094P, collided with a tree and the terrain following an in-flight separation of a tail rotor blade in El Dara, Illinois. Witnesses reported hearing the engine running rough followed by a loss of engine power just prior to the impact. The pilot was fatally injured. The helicopter was destroyed by impact and post impact fire. The 14 Code of Federal Regulations Part 91 personal flight was operating in visual meteorological conditions without a flight plan. The local flight originated from a private farm field in New Canton, Illinois, at about 0900. The pilot kept the helicopter on his property in New Canton. His wife stated was going to fly to El Dara to check on the crops. She stated that he usually flew at an altitude of about 400 feet above ground level (agl). There were four known witnesses to the accident. One of the witnesses stated he saw the helicopter flying east-southeast. He stated he then heard what sounded like the engine sputtering and the helicopter made two or three 360 degree turns prior to nose-diving toward the ground. A second witness reported seeing the helicopter flying to the southeast. This witness reported hearing the "engine cut out" followed by the sound of an impact. The third witness reported seeing the helicopter flying low to the ground. This witness reported the engine suddenly quit running and the helicopter started spinning prior to contacting the ground. The fourth witness stated the helicopter was flying 150 to 200 feet agl. The helicopter then started "misfiring and tail spun to the ground." PERSONNEL INFORMATION The pilot held a private pilot certificate with a rotorcraft helicopter rating issued March 6, 2004. The pilot held a third class medical certificate, which was issued on January 27, 2005. His medical certificate did not contain any limitations. At the time of his last airman medical examination, the pilot reported having 246 hours of flight time of which 12 hours were flown in the previous 6 months. In addition, the pilot held a Repairman certificate with an Experimental Aircraft Builder rating. This certificate was limited to Baby-Belle Model B-B, serial number 2053. Pilot logbook records were not located during the course of this investigation. AIRCRAFT INFORMATION N9094P was an amateur-built, single-engine, two-seat helicopter that was equipped with skids. The kit was manufactured by Canadian Home Rotors (CHR), Inc., Ontario, Canada. The helicopter was powered by a 160 horsepower Lycoming O-320 engine. According to a friend of the pilot, who also owned a Baby Belle, the pilot purchased the kit second-hand from a previous owner in 2000. The friend stated the kit was still packed in the original boxes when the pilot purchased it and nothing had been assembled. He stated the pilot built the helicopter and the first flight was in 2001. This friend estimated that the helicopter had approximately 250 hours of flight time on it at the time of the accident. According to CHR, the helicopter was involved in a hard landing in 2004. In 2005, the pilot purchased numerous replacement parts to repair the helicopter. An invoice provided by CHR shows that among the items purchased were main rotor blades and the tail rotor assembly including the spindle and blades. According to the pilot's friend, they balanced the new tail rotor blades after they were installed, but the blades continued to run "rough." A representative from CHR stated the pilot voiced his concerns to them and they sent out replacement tail rotor blades to the pilot. This representative stated he saw the pilot about a month before the accident and the pilot stated the helicopter was running fine since he installed the replacement tail rotor blades. The pilot's friend confirmed this information. The pilot's friend and CHR both stated the pilot was required to hover for 20-hours following the replacement of major components. The friend stated the pilot finished the 20 hour hover requirement and had probably flown an additional 5 hours. The friend stated the pilot flew the helicopter on the day prior to the accident, and he was not aware of any recent problems with the operation of the helicopter. Aircraft logbooks/records were not located during the course of this investigation. METEOROLOGICAL INFORMATION The closest weather reporting station was located at the Quincy Regional-Baldwin Airport (UIN) located approximately 22 miles north-northwest of the accident site. The UIN weather reported at 0854 was: Wind - 230 degrees at 4 knots; Visibility - 10 statute miles; Sky Condition - Few Clouds at 11,000 feet; Temperature - 21 degrees Celsius; Dew Point - 17 degrees Celsius; Altimeter Setting - 29.89 inches of mercury. WRECKAGE AND IMPACT INFORMATION The on-scene examination of the helicopter was conducted by inspectors from the Federal Aviation Administration (FAA) Flight Standards District Office in Springfield, Illinois. The inspectors reported the helicopter came to rest on its right side at the edge of a soybean field alongside a row of trees. The left fuel tank was ruptured and the cockpit area was consumed by the post impact fire. Both main rotor blades remained attached to the mast. One blade was intact with the outboard one-third of the blade bent upward. The inboard section of the other main rotor blade sustained fire/heat damage. All major components of the helicopter were located at the main wreckage site except for one of the tail rotor blades and the respective outboard 2 inches of the tail rotor spindle which, were not located. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was conducted on the pilot at the Memorial Medical Center, Springfield, Illinois, on August 29, 2005. A Forensic Toxicology Fatal Accident Report was prepared by the FAA Civil Aeromedical Institute, Oklahoma City, Oklahoma. The toxicology results for the pilot were negative for all tests performed. TEST AND RESEARCH The tail rotor assembly was sent to the National Transportation Safety Board's Materials Laboratory for examination. The examination revealed the tail rotor spindle contained two integral rods, which extended out in opposite directions. The length of each rod was manufactured with sections of consecutively reduced diameter. The examination revealed a fatigue failure was present which, initiated at the relief radius between the sections where the rod steps down from 0.812-inch diameter to 0.750-inch diameter. The relief radius in this area was rough and irregular and was measured to be approximately 0.0073-inch. CHR provided the engineering drawings for the tail rotor spindle to the NTSB. Drawing #15 did not specify a relief radius for the transition area between the 0.812-inch and 0.750-inch diameter sections. CHR subsequently provided a revised drawing #15, dated September 14, 2005. This drawing required a 0.0156-inch relief radius between the .812-inch and .750-inch diameter sections. CHR stated they did not manufacture the spindles. The manufacturing of the spindles were contracted out to an individual who owned a machine shop. ADDITIONAL INFORMATION Parties to the investigation were the Federal Aviation Administration and Lycoming Engines.