Primary finding
Probable cause
The pilot's delayed application of carburetor heat while operating in conditions conducive to carburetor icing.
Investigator assessment
Analysis narrative
The pilot reported that the airplane's engine began to run rough during level flight, with about a 70 percent power setting. He switched fuel tanks and applied carburetor heat, but the airplane's engine continued to run rough. The pilot initiated a forced landing to a cornfield during night light conditions. Postaccident examinations of the airplane revealed that the firewall was buckled. No anomalies were found with regard to the airplane, engine, or systems during the postaccident examinations. According to the Federal Aviation Administration icing probability chart, the airplane was operating in conditions conducive to carburetor icing at the time of the accident.
Source record
Factual narrative
The pilot reported that the airplane's engine began to run rough during level flight with about a 70 percent power setting. He switched fuel tanks and applied carburetor heat, but the airplane's engine continued to run rough. The pilot initiated a forced landing to a cornfield during night light conditions. Postaccident examinations of the airplane revealed that the firewall was bent/buckled. No anomalies were found with regard to the airplane, engine, or systems during the postaccident examinations. A weather report for the destination airport recorded the temperature and dew point as 18 degrees Celsius and 16 degrees Celsius respectively. According to a Federal Aviation Administration Special Airworthiness Information Bulletin, entitled Carburetor Icing Prevention, the temperature and dew point were conducive to the formation of carburetor icing.