On May 10, 2002, at 1315 eastern daylight time, a McDonnell Douglas MD-600N, N810LA, registered to a private owner, collided with the ground during a precautionary landing at Deland Municipal Airport, Deland, Florida. The personal flight was operated under the provisions of Title 14 CFR Part 91 and visual flight rules. Visual meteorological conditions prevailed at the time of the accident. The helicopter was substantially damaged and the private pilot and his passenger were not injured. The flight originated from Orlando Executive Airport, Orlando, Florida, on May 10, 2002 at 1245. According to the pilot, while enroute to Fernandina Beach, Florida, he observed an auto re-lite master caution indication on the annunciator panel. He diverted to the nearest airport to trouble shoot the situation. After calling air traffic control for the frequency to Deland Municipal Airport to make a precautionary landing, he observed an electronic control unit (ECU) failure indication. When the pilot switched the ECU switch from auto to manual position, and the engine started to over speed. He rolled the throttle back twice, and received a "fuel flow fix" voice warning indication. The pilot stated the engine started to make loud "bangs" like a compressor stall. The pilot stated he tried to maintain forward airspeed to clear trees. As the helicopter cleared the trees and power lines, the pilot received a voice warning "low rotor". During the emergency descent to land the pilot increased collective to arrest the descent. The "low rotor" warning light came on again and the helicopter landed hard. The main rotor blades came in contact with the tail boom and severed it from the airframe. On site examination of the helicopter revealed that the tail boom had been separated from the airframe. The engine was intact and it exhibited N1 and N2 shaft continuity throughout the drive train. All rigid and flexible oil and pneumatic lines were checked and found to be intact. All engine controls; hydro mechanical unit, electronic control unit, and combined engine filter assembly were intact. Fuel was present in the appropriate lines. The magnetic indicating plugs were also absent of any particles. A review of the maintenance fault page indicates a failed NG1 and NG2 sensors: NG1- Gas producer speed sensor, NG2- Gas producer sensor 2, as the primary contributor to the cockpit indications the pilot received. The engine was tested in accordance with a standard acceptance test with no deviations or points outside of acceptable service limits. The engine full authority digital electronic fuel control unit (FADEC) main harness (P/N-23064230, S/N-0099) and accessory harness (P/N-23068851, S/N-0026) were both subject to hand movements during the engine run with no deviations outside of the service limits. The faults could not be duplicated on the engine, sensors or harness. Inspection of the engine and engine accessories revealed no evidence of pre-impact component failures. Review of the MD 600N Rotorcraft Flight Manual, emergency and malfunction procedures, page 3-13, FADEC Malfunctions, states: NOTE: With an ECU failure, the engine fuel flow is fixed until the ECU Auto/Manual switch is placed in Manual. Changing the collective position with ECU switch still in Auto may result in higher or lower than normal Np/Nr speeds. · Reset ECU by momentarily placing the AUTO/MANUAL switch to MANUAL and then back to AUTO (2 reset attempts allowed). NOTE: Occasional electronic transients may produce a false ECU fail indication. If ECU Fail indication persists after 2 reset attempts, place switch in MANUAL. · AUTO/MANUAL switch to MANUAL at pilot's discretion. · Twistgrip: immediately reduce a given amount based on power setting. NOTE: The amount of twistgrip reduction required is based on setting (torque). Low power settings require a larger reduction to prevent Np/Nr overspeed. If no Twistgrip reduction is made, it takes from 4 seconds at lower power to 5 seconds at high power to see an increase in Np/Nr. Upon completion of Allison CEB-73-6033: If no twistgrip reduction is made, it takes from approximately 3 seconds at lower power to approximately 4 seconds at high power to see an increase in Np/Nr. · Twistgrip: manually control Np/Nr at 100%. NOTE: Occasional RPM transients between 90% and 106.4% are allowable as long as the maximum or minimum RPM limits are not exceeded. · Land as soon as practical · Advise maintenance