Cessna 172 - M N80257 accident near Hardin, Montana

Probable cause

A rough-running engine and partial loss of power, which resulted from the pilot’s failure to use carburetor heat appropriately while operating in an area conducive to carburetor icing.

NTSB analysis

The pilot reported that, during cruise flight, the engine began running roughly. He began troubleshooting the problem and turned on the carburetor heat but only for a few seconds. The pilot's attempts to restore full engine power were unsuccessful, so he chose to initiate an emergency landing to a field. During the landing flare, the airplane encountered a wind gust, which pitched the airplane's nose down. The nose gear dug into the soil, and the airplane nosed over.

A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Weather conditions in the area at the time of the accident were conducive to the formation of carburetor icing at cruise power. It is likely that the pilot did not apply carburetor heat long enough to prevent the accumulation of carburetor icing, which caused the engine to run roughly and lose partial power.

Text from the NTSB. Open the NTSB docket for WPR14LA023 for the full record.