On January 02, 2003, about 0900 mountain standard time, a turbine converted Bell 47G helicopter, N4759R, sustained substantial damage after a loss of engine power, autorotation, and hard landing eight miles southeast of Idaho Falls, Idaho. The helicopter is owned and operated by Heli-Wood of Tremonton, Utah, and was being operated as a visual flight rules (VFR) positioning flight in accordance with Title 14, CFR Part 91, when the accident occurred. The commercial pilot, the sole occupant of the helicopter, was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the flight. The flight originated from an off-airport site approximately five miles east of Idaho Falls, approximately six minutes prior to the accident. The pilot reported that while in a cruise flight configuration, at 5,100 feet MSL and 80 MPH, the helicopter experienced a loss of engine power and the pilot initiated a forced landing to a nearby alfalfa field. During the landing, the main rotor blades made contact with the tail boom assembly, severing the top two tubes just aft of the last hangar bearing. Visual inspection of the helicopter's engine and associated components revealed no evidence of atypical wear or component failure. Inspection of the fuel system revealed that: the fuel inlet lines and vent lines were intact and no restrictions or leakage was noted. The fuel pump filter, airframe fuel filter, fuel control inlet screen and fuel nozzle inlet screen were intact and free of contaminants. Soot and carbon deposits were noted on the fuel nozzle tip. The Pc lines and associated components were intact and no cracks or evidence of leakage was noted. Following the visual inspection, the operator conducted an engine run. The engine was started and ran at various power settings for approximately 10 minutes. No power surges or anomalies were noted during test run. The operator and a representative from the Salt Lake City Flight Standards District Office conducted the post accident inspection and subsequent test run.