Cessna 172N N4922G accident near San Rafael, California

Probable cause

The total loss of engine power due to carburetor icing as a result of the pilot’s failure to activate the carburetor heat in a timely manner during the descent.

NTSB analysis

The pilot was on a night cross-country flight and began an enroute descent about 65 miles from the destination airport. When the pilot attempted to add engine power to level off at a lower altitude, the engine did not respond. The pilot attempted to troubleshoot the loss of engine power, including selecting carburetor heat, but without success. As the airplane continued to descend, it struck a powerline near the approach end of the runway and impacted a water canal. During the accident sequence the fuselage and both wings sustained substantial damage.

The pilot did not report that he activated the carburetor heat during the descent, as called for in the pilot’s operating handbook normal descent procedures “as required – for carburetor icing conditions.” The pilot reported that he would not normally select the carburetor heat until the airplane was below 1500 ft and entering the traffic pattern.

Postaccident examination of the airplane revealed no evidence of any preaccident mechanical malfunctions or failures that would have precluded normal operation. Review of weather information indicated that the airplane was operating in an area conducive to the development of serious carburetor icing at cruise power. It is likely that the carburetor accumulated ice during the prolonged descent without the use of carburetor heat, which resulted in a total loss of engine power.

The accident is consistent with a total loss of engine power due to carburetor icing as a result of the pilot’s failure to activate the carburetor heat in a timely manner during the descent.

Text from the NTSB. Open the NTSB docket for WPR23FA258 for the full record.