Cessna 177B N925KM accident near Mashpee, Massachusetts

Probable cause

The pilot’s delayed use of carburetor heat while flying at reduced power settings in conditions that were favorable for carburetor icing resulting in the partial loss of engine power.

NTSB analysis

The flight had been flown at a reduced power setting and about 2 hours and 5 minutes into it, the pilot moved the propeller control to the low pitch position and applied the carburetor heat. The engine lost power and in response, the pilot removed the carburetor heat and then attempted to restore engine power by reapplying carburetor heat and switching the fuel selector to another tank. The engine only responded for a few seconds and lost power again. He maneuvered the airplane for a forced landing and ditched near a shoreline. A postaccident examination of the engine and engine accessories by a Federal Aviation Administration inspector revealed no evidence of mechanical failures or malfunctions that could have contributed to the loss of engine power. Based on the temperature and dew point about the time of the accident, the conditions were favorable for serious icing at glide power.

Text from the NTSB. Open the NTSB docket for ERA10LA396 for the full record.