Primary finding
Probable cause
The delayed application of carburetor heat by the pilot which led to accumulation of carburetor ice, eventual loss of engine power, and the subsequent forced landing in high vegetation.
Investigator assessment
Analysis narrative
The pilot reported that while descending from cruise flight to traffic pattern altitude, the airplane's engine began to run rough. He applied carburetor heat which made the roughness worse and when he then turned off carburetor heat, the engine lost all power. The pilot executed a forced landing to a farm field where the airplane nosed over in the high vegetation. According to a carburetor icing probability chart, the temperature and dew point were in the range of susceptibility for serious carburetor icing at descent power settings. The pilot's report of the accident listed no mechanical malfunctions or failures of the airplane, and a recommendation to apply carburetor heat earlier at the beginning of the descent. Based on the information available the airplane's engine likely lost power due to accumulation of carburetor ice due to the delayed application of carburetor heat.
Source record
Factual narrative
On August 31, 2018, about 1345 eastern daylight time, a Cubcrafters CC11-160 airplane, N71BN, sustained substantial damage to the left-wing strut when it nosed-over during a forced landing to a soybean field following a complete loss of engine power. The airplane was descending to land at the Fairfield County Airport (LHQ), near Lancaster, Ohio. The pilot was not injured. The aircraft was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as personal flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight originated from The Duchy Airport (5NC5), Chapel Hill, North Carolina, about 1045, and was destined for LHQ. The pilot reported that while descending from cruise flight to traffic pattern altitude, the airplane's engine began to run rough. The pilot applied carburetor heat which made the roughness very bad and he turned the carburetor heat off. When he did this, the engine lost all power. The airplane's altitude was about 2,000 ft. msl (1,200 ft. agl), and the pilot performed an off-airport landing to a farm field. During the landing, the airplane nosed over in the waist-high vegetation. The pilot reported that there were no mechanical malfunctions or failures of the airplane, and noted earlier use of carburetor heat at the beginning of the descent as an operator recommendation. The weather conditions at LHQ about the time of the accident included a recorded temperature of 28° C and a dew point of 21° C. According to a carburetor icing probability chart, this was in the range of susceptibility for serious icing during descent power settings.