Accident Details
On July 13, 2019, about 1145 eastern daylight time, a Cessna 120, registration N3886V, was substantially damaged in an accident near Summit, South Carolina. The commercial pilot, operating the airplane under 14 CFR Part 91 as a personal flight, was not injured.
The pilot reported conducting a preflight inspection that included checking the wing fuel tanks and fuel strainer for contaminants; none were found. He departed and after about 30 minutes switched the fuel selector to the left tank and returned to the airport for touch-and-go landings. During descent and approach, he applied carburetor heat when the engine was below 1,200 rpm and regularly increased engine power to clear it. After touchdown, he pushed carburetor heat off and applied full throttle for takeoff. At about 40 to 50 feet above ground level, the engine lost power. He slipped the airplane to lose altitude and landed on the remaining runway. During the landing roll, he applied brakes to prevent a runway overrun, causing the airplane to nose over and come to rest inverted.
Engine Examination
Post-accident examination revealed that impact damage to the intake manifold assembly precluded an engine run. A mechanic examined the engine after recovery. The fuel strainer and carburetor bowl contained blue liquid consistent with 100 low lead aviation fuel, with slight particulate contamination in the bowl. No blockages were found in the air induction, exhaust, fuel vent, or fuel supply system from each tank to the engine through the fuel selector valve in both left and right positions. Compression was established for each cylinder, and a borescope inspection showed no anomalies except some discoloration on the No. 2 exhaust valve. The left magneto was timed at 27.5° before top center (BTC) (specification 30° BTC), and the right magneto at 20° BTC (specification 28° BTC). All spark plugs indicated a rich fuel/air mixture. Carburetor heat control continuity from the cockpit to the airbox was confirmed, and the carburetor heat was in the off position; impact damage to the door at the airbox prevented activation from the cockpit.
Weather and Carburetor Icing Information
Weather recorded at Columbia Metropolitan Airport, about 16 miles west, at 1156 included a temperature of 32°C and dewpoint of 22°C, with a calculated relative humidity of about 58 percent. The icing probability chart in FAA Special Airworthiness Information Bulletin CE-09-35 indicated that atmospheric conditions were conducive to icing at glide (idle) and cruise power. The FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B) recommends full application of carburetor heat before reducing the throttle for closed throttle operation if carburetor icing conditions are anticipated, and to leave it on during closed-throttle operation, with periodic throttle openings to keep the engine warm.