On August 4, 2005, approximately 0730 Pacific daylight time, an experimental Steele Safari helicopter, N13MA, rolled over during an emergency landing about six miles north of Leavenworth, Washington. The commercial pilot, who was the sole occupant, was not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal cross-country flight, which departed Cashmere Airport, Cashmere, Washington, about 15 minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed. There was no report of an ELT activation. According to the pilot, while in cruise flight about 1,000 feet above ground level (agl), he heard a loud grinding sound and felt a significant vibration in the airframe of the helicopter. The aircraft then swung to the right, so the pilot elected to reduce the throttle and perform an autorotation to a nearby open field. During the attempted autorotational landing on the soft grassy terrain, the aircraft touched down, bounced back into the air, turned about 300 degrees, and then touched down a second time. During the second touchdown, the skids dug into the soft terrain, and aircraft rolled over onto its left side. During the accident sequence, the main rotor blades flexed downward and came in contact with the tail boom. When the pilot inspected the helicopter at the scene, he found that all of its components, except for the tail rotor drive shaft, were there at that one location. Although he searched the local area for the tail rotor drive shaft, he was unable to locate it. The drive shaft was later found by a local resident several hundred feet from the location where the helicopter touched down. After being recovered to a hangar in Everett, Washington, the aircraft was inspected by an FAA Airworthiness Inspector from the Seattle, Washington, Flight Standards District Office. It was his determination that the tail rotor drive shaft had failed in cruise flight at a location near where it attaches to the main rotor transmission assembly. The reason for the failure of the shaft could not be positively determined.