Accident Overview
On September 12, 2024, at approximately 1205 central daylight time, a Piper PA-12 airplane, registration N7878M, was substantially damaged during an accident near Cumberland, Wisconsin. The pilot was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Report
The pilot reported that the airplane was in cruise flight at 2,100 ft mean sea level with the throttle set at about 2,300 rpm and the mixture leaned to rich-of-peak. During a descent toward Cumberland Municipal Airport, the pilot made no changes to throttle or mixture, and the engine was receiving fuel from both wing tanks.
Approximately 5 miles from the airport, while in cruise descent, the engine began to sputter and then suddenly lost power. The pilot advanced the throttle to full-forward and enriched the mixture to full-rich. The engine briefly resumed operation for 5-10 seconds before quitting again. Due to low altitude, an immediate forced landing was made in a nearby cornfield. The airplane sustained substantial damage to the engine mounts, fuselage structure, and right wing.
Aircraft Examination
Post-accident examination of the fuel system and engine revealed no evidence of a preimpact mechanical malfunction. Ample fuel was recovered from the tanks, with no water or particulate contamination. Internal engine continuity was confirmed, compression and suction were noted on all four cylinders, and both magnetos produced spark. Borescope inspection of cylinders, pistons, valves, and valve seats showed no anomalies. Upper spark plugs appeared normal, and the oil sump contained ample clean oil.
The throttle cable was broken at the clevis, but the carburetor throttle remained in a wide-open position. The mixture control was found in full-rich, with the full-rich mechanical stop-pin fractured. The carburetor heat control in the cockpit was off. Cable continuity from the control to the airbox was confirmed, but impact damage prevented the carburetor heat valve from moving. Borescope inspection of the airbox found no evidence of rubbing or scratching on the valve.
Carburetor Icing Conditions
According to a carburetor icing probability chart from FAA Special Airworthiness Information Bulletin CE-09-35, the recorded temperature and dew point at the time of the accident were in the range of susceptibility for serious carburetor icing at glide engine power. The bulletin notes that ice formation in a fixed-pitch propeller aircraft can restrict induction airflow, causing power loss and engine roughness. It recommends applying full carburetor heat immediately and using heat during low power settings or in icing-prone conditions.
During a follow-up interview, the pilot stated he did not review a carburetor icing chart before the flight but applied carburetor heat after the engine began sputtering.