Robinson Helicopter R44 N444VH accident near East Troy, Wisconsin

Probable cause

A partial loss of engine power for reasons that could not be determined based on the available information, which resulted in impact with terrain and dynamic rollover during the subsequent attempted landing.

NTSB analysis

The flight instructor and pilot receiving instruction were maneuvering to begin practice hovering when the helicopter experienced a lateral vibration. The instructor assumed control of the helicopter and attempted to land; however, the helicopter yawed to the left and both the instructor and pilot applied full right pedal to align the helicopter's nose with its ground track. Shortly thereafter, they heard the low rotor rpm horn and saw the associated warning light illuminate. The helicopter continued to the left, and as they lowered to the ground, the right skid caught on the grass and the helicopter experienced a dynamic rollover, resulting in substantial damage to the main rotor blades and fuselage.

Examination of the airframe and engine revealed no preimpact mechanical malfunctions or failures that would have precluded normal operation, and the helicopter had adequate fuel onboard for the flight. Although the weather conditions at the time of the accident were conducive to the formation of carburetor icing at glide and cruise power, the helicopter was equipped with a carburetor heat assist device, which automatically applied or reduced carburetor heat with changes in collective input. The reason for the partial loss of engine power could not be determined based on the available information.

Text from the NTSB. Open the NTSB docket for CEN18LA158 for the full record.