Accident Details
On April 5, 2012, about 0700 mountain daylight time, a Robinson R22 Beta helicopter, registration N104MH, impacted terrain while maneuvering at low altitude near Isabel, South Dakota. The pilot was seriously injured; the passenger was not injured. The helicopter was substantially damaged. The helicopter was registered to and operated by the pilot under 14 Code of Federal Regulations Part 91 as a coyote hunting flight. Day visual meteorological conditions prevailed, and no flight plan was filed. The flight departed Timber Lake Municipal Airport (D58), Timber Lake, South Dakota, about 0630 for the local flight.
Pilot Account
The pilot reported that he was flying southbound at about 50 to 70 knots, at an altitude of 50 feet or more above ground level (AGL), with a surface wind out of the southeast. He made a sudden steep right turn to the west to intercept a coyote when he felt a loss of engine power, heard a low rotor horn, and immediately dumped the collective. The helicopter impacted trees and terrain and rolled onto its right side. There was a minor fuel leak, but no postimpact fire. After the helicopter came to rest, both occupants extracted themselves from the wreckage. The injured pilot stayed with the wreckage while the passenger walked several miles in the remote rural area to a residence to call 9-1-1.
Postaccident Examination
A postaccident examination of the helicopter found an adequate amount of uncontaminated fuel. The tips of the main rotor blades were curved up almost 90 degrees from horizontal. There was little evidence of rotational impact damage on the leading edges of the main rotor blades and tail rotor blades. No preimpact anomalies were found that would have prevented normal operation.
Weather Conditions
The nearest aviation weather reporting station, Mobridge Municipal Airport (KMBG), about 44 miles northeast of the accident site, reported at 0652: wind 130 degrees at 11 knots, visibility 10 miles, few clouds at 3,900 feet AGL, temperature 7°C, dew point -1°C, altimeter 29.87 inHg. A weather reporting station at Timber Lake, about 15 miles northeast, reported at 0700: average temperature 37°F, average humidity 71%, wind from 133 degrees at 8 mph gusting to 15 mph. The carburetor icing probability chart from FAA Special Airworthiness Information Bulletin No. CE-09-35 indicates that an aircraft operating in the ambient conditions at the time of the accident could expect a serious risk of accumulating carburetor ice at any power setting. The FAA Pilot's Handbook of Aeronautical Knowledge states that when conditions are conducive to carburetor icing, carburetor heat should be applied immediately and left on until all ice is removed. The pilot reported that he was unsure if he had used carburetor heat for the accident flight.