On September 23, 1999, approximately 0900 mountain daylight time, a Bell 47G3B2A helicopter, N83246, registered to and operated by the pilot and doing business as Helowood Helicopters, was substantially damaged during a forced landing following a loss of engine power while maneuvering 2 miles southeast of Tremonton, Utah. The commercial pilot, the sole occupant aboard, was not injured. The aircraft was being operated as a ferry flight under Title 14 CFR Part 91, and a company VFR flight plan had been filed. The flight originated from the Tremonton Municipal Airport, Tremonton, Utah, 5 minutes prior to the accident, and was en route to Coalville, Utah. Visual meteorological conditions prevailed. According to the pilot, he was flying to a local staging area for the purpose of conducting aerial application work. He departed with 30 gallons of fuel and was planning to pick up a load of chemical spray at his destination. Approximately two and a half miles southeast of Tremonton, the engine began "running rough," and he attempted to return to the airport. The engine continued to "miss," and one half a mile after turning around he decided to make a precautionary landing in an alfalfa field. At that time, "the engine was running well enough to land with power." However, when the helicopter was 200 feet above ground level (agl), the engine began to run rougher and he initiated an autorotation. He closed the throttle completely and the engine quit. The helicopter touched down with a forward airspeed of 2 to 3 miles per hour. The aircraft stopped suddenly and rocked forward. The rotor blades flexed downward, severing the tail boom. The day following the accident, an examination of the engine was performed by an FAA maintenance inspector. According to the inspector's statement, he removed the rear spark plugs and they appeared to be in satisfactory condition. A compression test was performed and no discrepancies were noted. No apparent damage to the cylinders was observed. The magnetos were satisfactorily checked for timing, and the carburetor was found to be securely and accurately installed. The maintenance records were reviewed and found to be "complete and satisfactory." Fuel samples were taken from the carburetor and were found to be clear and free of contaminates. The engine was unable to be functionally tested due to the damage caused by the main rotor blades. According to the inspector, "No cause could be determined for the engine's unsatisfactory performance" (see attached statement). When asked in the NTSB Pilot/Operator Aircraft Accident Report (Form 6120.1/2) what recommendation the pilot could make as to how the accident could have been prevented, he responded that he could have "performed [a] better autorotation."