On March 13, 2012, about 1745 eastern daylight time, an experimental amateur-built, CHR Safari helicopter, N105KM, operated by a private individual, was substantially damaged during an autorotation in Hixson, Tennessee. The private pilot was not injured and a passenger was seriously injured. Visual meteorological conditions prevailed and no flight plan was filed for the local personal flight that was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The two seat helicopter was co-owned and co-built by the pilot. It was powered by a non-certified Superior XP IO-360 series, 380-horsepower engine and issued an experimental airworthiness certificate on September 23, 2009. The pilot stated he flew about 1 mile from his home to reach the passenger's property. He landed in an open field and secured the helicopter before assisting the passenger on board. The helicopter was started and lifted off without incident. At an airspeed of approximately 45 knots, and between 100 and 150 feet above the ground, "the engine shuttered for an instant and came back to normal." The pilot stopped the climb, confirmed that all engine instruments were "in the green" and began a left turn back toward the takeoff area. About halfway into the 180-degree turn, the engine shuttered again. The pilot applied full throttle with no engine response and observed the engine rpm drop from about 2,700 to about 1,500, with the rotor speed in the middle of the green indicator. He then entered an autorotation and landed on top of a tree, which began to bend over, and lowered the helicopter toward a creek below. As the helicopter reached the water, it rolled on to its side and fell about 3 feet into the creek. The pilot was able to assist the passenger out of the helicopter during the time in which a fire erupted from the engine compartment. The fire was contained with water from the creek until it was extinguished by the local fire department. Examination of the helicopter by a Federal Aviation Administration inspector did not reveal any preimpact mechanical malfunctions that would have precluded normal operation. The engine crankshaft rotated freely, compression was obtained on all cylinders and proper magneto function was noted. Fuel mixed with water was found in the gascolater; consistent with being submerged in the creek. Damage sustained to the engine during the impact and postaccident fire prevented the ability to have it operationally test run. Additional detailed examinations of the helicopter, which included examinations of the engine, clutch and transmission systems by the helicopter kit manufacturer, did not reveal any preimpact failures. In addition, the kit manufacturer conducted a series of test flights utilizing a similarly equipped and configured helicopter in an attempt to determine if clutch slippage could be induced under normal flight conditions. According to the kit manufacturer, clutch slippage could only be induced under conditions which were well outside the helicopter's normal operating parameters and standard procedures, such as allowing the rotor rpm to decay below 450 rpm and rapid application of the collective or throttle controls. The helicopter was equipped with a Dynon EMS-D10 engine monitor which was configured to record information at 5 second intervals to non-volatile-memory. The engine monitor was successfully downloaded at the NTSB Vehicle Recorder Laboratory, Washington, DC. Review of the data did not reveal any drops in engine rpm or any other anomalies consistent with the pilot's statement. The data during about 30 seconds prior to the autorotation showed consistent fuel flows, fuel pressures, and manifold pressures, with rpm mostly in the 2,700-2,740 range and never dropping below about 2,600 rpm. At the time of the accident, the helicopter had been operated for about 130 total hours, and about 75 hours since its most recent condition inspection, which was performed on June 20, 2011. The pilot/co-owner reported 1,230 hours of total flight experience, which included about 380 hours in helicopters, and approximately 147 hours in the same make and model as the accident helicopter. In addition, he had flown the accident helicopter 26 hours and 3 hours, during the 90 and 30 days that preceded the accident; respectively.