ERA23LA275 · Aeronca 11AC

The pilot reported that he reduced power while leveling off in the airport traffic pattern, at an altitude of 1,000 feet above ground level, then subsequently felt as though the airplane was sinking. He noticed that the engine rpm was at 1,500 and there was no forward thrust. He attempted to troubleshoot, applied carburetor heat, and lowered the nose to maintain glide speed, but was unable to restore engine power before the airplane descended into trees, resulting in substantial damage to the fuselage and wings. Postaccident examination of the engine revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal engine operation, with the exception that the carburetor heat tubing was not completely attached to the carburetor intake box. It did not display evidence of impact damage. The disconnected tubing would likely have resulted in a reduced quantity of heated air reaching the carburetor and would have reduced the system’s effectiveness. The weather conditions at the time of the accident were conducive to the formation of serious carburetor icing at glide engine power settings. Based on the available information, it is likely that the loss of engine power was the result of carburetor ice accumulation. While the pilot reported that he did not utilize carburetor heat until after he thought the engine had lost power, which would have substantially reduced the likelihood that it could have eliminated any accumulated icing in the carburetor, given the findings that the system may not have been operating properly when the engine lost power, even timely activation may not have impacted the outcome.

Verbatim NTSB analysis and probable cause from the NTSB dataset