On October 26, 2013, at 1300 central daylight time, a Bell OH-58A helicopter, N283MP, was substantially damaged during a forced landing near the Jefferson City Memorial Airport (JEF), Jefferson City, Missouri. The pilot receiving instruction sustained minor injuries. The flight instructor was not injured. The public-use helicopter was registered to and operated by the Missouri State Highway Patrol, under the provisions of 14 Code of Federal Regulations Part 91, without a flight plan. Day visual meteorological conditions prevailed for the local area training flight that had departed JEF at 1215. The pilot receiving instruction reported that the purpose of the flight was to remain in the traffic pattern for runway 30 while practicing autorotation landings. He stated that after approximately 45 minutes of flight training, the engine began to fluctuate between full and half power while the helicopter was climbing on a downwind leg. The helicopter also experienced an uncommanded yaw with each engine power fluctuation. The flight instructor took control of the helicopter and entered a straight-in autorotation from an altitude of less than 1,000 feet above the ground. The pilot receiving instruction reported that the gas generator speed was less than 50 percent, the turbine temperature was about 300 degrees Celsius, and the main rotor speed was at 100 percent during the autorotation. The flight instructor began the landing flare about 50 above the ground and the helicopter touched down in a level attitude. However, shortly after touchdown, the helicopter rotated to the left after a landing skid dug into the soft terrain. The flight instructor reported that the helicopter experienced an intermittent left yawing motion that he associated with an interruption in engine power. Believing that a total loss of engine power was imminent, he took control of the helicopter and entered a straight-in autorotation toward a nearby open field. He stated that the helicopter touched down with a slight forward ground run, during which the left skid dug into the soft soil causing the helicopter to rotate 180-degrees before it came to a stop. The main rotor blades severed the tail boom from the fuselage during the forced landing. At 1253, the JEF automated surface observing system reported: wind from 270 degrees at 13 knots, gusting 17 knots, visibility 10 miles, sky clear, temperature 16 degrees Celsius, dew point 4 degrees Celsius, and an altimeter setting of 30.08 inches-of-mercury. A postaccident examination revealed no airframe or engine anomalies that would have prevented normal operation of the helicopter. The helicopter fuel system contained about 350 pounds of Jet-A fuel that was free of water and particulate contamination. The airframe fuel filter element was free of any particulate contamination. With electrical power applied, the airframe fuel boost pump functioned as designed and no leaks were identified throughout the fuel system. Engine control continuity was established from the cockpit controls to the respective engine components. The engine magnetic chip detectors were clear of any metallic debris. No anomalies were identified with the engine's external air, fuel, and oil line connections. The engine fuel nozzle produced a normal spray pattern as the engine was rotated by the starter motor. The engine was removed from the airframe and shipped to the manufacturer for an operational test run. Before the engine test run, the pneumatic system was pressurized with shop air and no leaks were detected. The accident engine, a Rolls-Royce model T63-A-720, serial number AE 405896, was tested in accordance with the manufacturer's production specification. The engine demonstrated normal operation at all power settings and was capable of producing maximum takeoff horsepower.