Cessna 180 N4601A accident near Chugiak, Alaska

Probable cause

The pilot’s delayed use of carburetor heat while operating in conditions conducive to carburetor icing.

NTSB analysis

The airline transport pilot reported that he was approaching his destination airport at the conclusion of a local personal flight. He said that while in cruise flight at 1,200 feet above ground level, the engine began to run rough and lose power. He noticed that the carburetor air temperature was just above the carburetor ice zone marked in red on the gauge, so he applied full carburetor heat, which was followed by a complete loss of engine power. Unable to restart the engine, he selected a marshy tree-covered site as a forced landing area. The airplane sustained substantial damage to the fuselage and wings during the forced landing. A Federal Aviation Administration airworthiness inspector’s postaccident inspection disclosed no evidence any preimpact mechanical problems. An aviation weather reporting station indicated that the temperature was 57 degrees F, and the dew point was 45 degrees F. When these values are entered into a carburetor icing probability chart, the results are in the "serious icing-cruise power" category. Given the lack of any mechanical anomalies it is likely that the formation of carburetor ice resulted in the loss of engine power.

Text from the NTSB. Open the NTSB docket for ANC09LA086 for the full record.