CEN12LA230

While maneuvering at low altitude during a coyote hunting operation, the helicopter experienced a partial loss of engine power. The helicopter descended, impacted trees and terrain, and rolled on its right side. There was a minor fuel leak but no postimpact fire. A postaccident examination of the helicopter did not reveal any evidence of preimpact mechanical malfunction or failures that would have precluded normal operation. Based on the temperature and dew point about the time of the accident, the conditions were conducive to serious carburetor icing at any power setting. The pilot reported that he was unsure if he had used carburetor heat for the accident flight. Available evidence suggests that the engine partially lost power in the absence of carburetor heat while operating in conditions conducive to carburetor icing.

On April 5, 2012, about 0700 mountain daylight time, a Robinson R22 Beta helicopter, N104MH, impacted terrain while maneuvering at low altitude near Isabel, South Dakota. The pilot was seriously injured and the passenger was not injured. The helicopter was substantially damaged. The helicopter was registered to and operated by the pilot, under the provisions of 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. The pilot reported that he was flying about 50 to 70 knots southbound about 50 feet or more above ground level (AGL) with the 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 he immediately "dumped the collective". The helicopter impacted trees and terrain and rolled on its right side. There was a minor fuel leak, but no postimpact fire. After the helicopter came to rest both occupants were able to extract 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 make a telephone call to 9-1-1 emergency. A postaccident examination of the helicopter showed an adequate amount of uncontaminated fuel was present. The tips of the main rotor blades were curved up almost 90 degrees up from the 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 which would have prevented normal operation. The nearest aviation weather reporting station was located at Mobridge Municipal Airport (KMBG), Mobridge, South Dakota, about 44 miles northeast from the accident site. At 0652, the KMBG automated surface observing system reported the following weather conditions: wind 130 degrees at 11 knots, visibility 10 miles, few clouds at 3,900 feet AGL, temperature 7 degrees Celsius, dew point minus 1 degree Celsius, and an altimeter setting of 29.87 inches of Mercury. A weather reporting station was located at Timber Lake, South Dakota, about 15 miles northeast from the accident site. At 0700 the Timber Lake reporting station reported an average temperature of 37 degrees Fahrenheit, and an average humidity of 71 percent. The wind was reported as 8 miles per hour gusting to 15 miles per hour from 133 degrees. The carburetor icing probability chart included in Federal Aviation Administration (FAA) Special Airworthiness Information Bulletin No. CE-09-35, Carburetor Icing Prevention, 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 areconductive to carburetor icing that carburetor heat should be applied immediately and should be left on until the pilot is certain all the ice has been removed. Additionally, if ice is present the application of partial carburetor heat or leaving heat on for an insufficient time might aggravate the situation. The pilot reported that he was unsure if he had used carburetor heat for the accident flight.