CEN24LA362 · Cessna 172N

The pilot reported that during the flight, at an altitude of 1,800 ft above the ground, she encountered an area of light rain, so she applied carburetor heat as a precaution. Once carburetor heat was applied, the engine began to run rough and lose power. The pilot turned the carburetor heat on and off a few times because she was not sure if the introduction of the carburetor heat was making the loss of power worse. The pilot also completed the checklist for engine roughness. Unable to clear up the engine roughness and unable to maintain airplane altitude, the pilot performed a forced landing. The fuselage and right wing sustained substantial damage when the airplane impacted trees and terrain. A postaccident examination of the engine and fuel system did not reveal any preexisting anomalies or failures that would have precluded normal operation. Ample fuel drained from the wing fuel tanks before the wreckage was recovered; however, the amount of fuel drained was not documented. The recorded temperature and dew point near the accident site were conducive to “serious icing” at cruise engine power settings. Based on this information, it is likely that carburetor ice formed and there was insufficient time/altitude for the carburetor heat to melt the accumulated ice.

Verbatim NTSB analysis and probable cause from the NTSB dataset