Primary finding
Probable cause
The pilot's failure to maintain clearance from the terrain. Factors contributing to the accident were the whirlwind, the turbulence, and the helicopter's low altitude.
Investigator assessment
Analysis narrative
The helicopter impacted terrain after encountering a reported "whirlwind." The pilot reported he was on a spray pass at a "good altitude" and at 55 miles per hour. The pilot noted he saw the whirlwind but was not concerned. The pilot stated, "suddenly it felt [he] was slammed into the ground and out of control." The pilot reported the helicopter cartwheeled about 60 to 100 feet before coming to a stop.
Source record
Factual narrative
On June 27, 2003, at 1745 central daylight time, a Hiller UH-12E, N62417, owned and operated by a commercial pilot, was destroyed when it impacted terrain four miles south of Elk Mound, Wisconsin. Visual meteorological conditions prevailed at the time of the accident. The pilot reported minor injuries. The 14 CFR Part 137 aerial application flight was not operating on a flight plan. The local flight departed Stocktrade Airport (WI05), Elk Mound, Wisconsin, at 1737. The pilot reported he saw a "whirlwind" while on his last spray pass over the field. The pilot described the whirlwind as "about as wide as [the helicopter] rotorwash" and that it was "thrashing the potato vines similar to what a helicopter would do [while] hovering." The pilot noted he "seemed to have good altitude [and] spray speed of 55 [miles per hour]." The pilot stated, "suddenly it felt [the helicopter] was slammed into the ground [and was] out of control." The pilot reported the right spray boom impacted the terrain, and the helicopter cartwheeled about 60-100 feet before stopping. The pilot reported there were no mechanical malfunctions or failures during the accident flight.