Amateur-built 162 F N426DM accident near Maybee, Michigan

Probable cause

A partial loss of engine power for undetermined reasons.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for CEN24LA249 for the full record.