Primary finding
Probable cause
A partial loss of engine power for undetermined reasons.
Investigator assessment
Analysis narrative
The pilot reported that his preflight inspection of the experimental helicopter revealed no anomalies. About one hour into the flight, the engine and rotor rpm started to drop. When the pilot adjusted the collective and throttle, rotor rpm surged, and engine rpm began to fluctuate. The pilot selected a field and performed a precautionary autorotation. During the touch down, the helicopter’s skids dug into the soft soil and the helicopter spun, which resulted in substantial damage to the main rotor blades, fuselage, and the tail boom. The pilot and the passenger exited the helicopter uninjured. A postaccident examination of the helicopter revealed that fuel remained in the fuel tanks. Examination of the fuel-injected engine did not detect any anomalies that would have precluded normal operation. A roll of blue masking tape was found in the engine cooling shroud, but not in an area that would have interfered with engine operation. Given the lack of anomalies found during the postaccident examination, the reason for the partial loss of engine power could not be determined.
Source record
Factual narrative
On July 4, 2024, about 1043 eastern daylight time, an experimental Rotorway 162 F helicopter, N426DM, sustained substantial damage when it was involved in an accident near Maybee, Michigan. The pilot and passenger were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he conducted a preflight inspection of the helicopter, added fuel, and sumped the fuel tanks. No problems were noted on the preflight. The pilot brought the helicopter into a hover for takeoff, and all the systems checked normal. The pilot took off, climbed the helicopter to about 1,800 ft, and flew locally for about one hour with no problems. Nearing the end of the flight, the pilot noticed that the engine and rotor rpm started to drop. After he adjusted the collective and throttle, the rotor rpm surged, and engine rpm fluctuated. The pilot decided to perform a precautionary autorotation to a field. As the helicopter descended toward the field, the pilot adjusted the cyclic and collective to keep the airspeed at 70 knots, and rotor rpm about 100%. As the helicopter approached the field, the pilot flared the helicopter to arrest the forward momentum. The helicopter contacted the ground with some forward momentum, and the skids dug into soft soil. The tail boom contacted the ground, the helicopter nosed forward, spun about 120°, and came to rest upright, which resulted in substantial damage to the main rotor blades, fuselage, and the tail boom. The pilot and the passenger exited the helicopter uninjured. An examination of the fuel-injected engine was conducted by a certificated mechanic with oversight from the FAA. No anomalies were detected with the engine that would have precluded normal engine operation. Fuel was found in the fuel tanks. A roll of blue masking tape was found in the engine cooling shroud, but not in an area that would result in a loss of engine or rotor rpm.