On May 4, 2018, at approximately 1155 central daylight time, a Robinson R44 helicopter, registration N444VH, sustained substantial damage in an accident near East Troy, Wisconsin. The flight instructor and the pilot receiving instruction were uninjured. The helicopter was operating under Title 14 Code of Federal Regulations Part 91 as a training flight for Part 137 aerial application operations.
Accident Sequence
The flight instructor directed the pilot to hover-taxi the helicopter to a grass runway for hovering practice. The pilot reported experiencing a lateral vibration once over the runway, which the instructor described as loud. The instructor then assumed control to land. The helicopter was approximately 5 to 7 feet above the ground when it began to settle and yawed left by 30° to 40°. Both the instructor and pilot applied full right pedal to align the nose with their ground track. At about 2 feet above ground, the low rotor rpm warning system activated, with an illuminated light and sounding horn. The instructor raised the collective to cushion the landing, but the helicopter continued moving left. The right skid contacted the ground, initiating a dynamic rollover, and the helicopter came to rest on its right side.
Aircraft and Operational Context
The instructor had been conducting refresher training for spray pilots for approximately 2.5 hours before the accident flight. Neither the pilot nor the instructor reported using carburetor heat during the flight. The helicopter was equipped with a carburetor heat assist device that automatically correlated carburetor heat application with collective position: lowering collective applied heat, raising collective reduced it.
Post-Accident Examination
Substantial damage occurred to the main rotor system and fuselage. Examination of the airframe and engine revealed no preimpact mechanical malfunctions or failures that would have precluded normal operation. The instructor reported that an adequate amount of fuel was onboard for the flight.
The temperature and dewpoint at the time of the accident were conducive to the formation of serious carburetor icing at cruise power settings, according to the Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35 on carburetor icing prevention.