N3886VCessna 120 · 1947

On July 13, 2019, about 1145 eastern daylight time, a Cessna 120, N3886V was substantially damaged when it was involved in an accident near Summit, South Carolina. The commercial pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot stated that he performed a preflight inspection of the airplane which included a check of the wing fuel tanks and fuel strainer for contaminants; none were found. He departed, and after about 30 minutes, he switched the fuel selector to the left tank and returned to the airport to perform touch-and-go landings. The pilot applied carburetor heat during the descent and approach when the engine was operating below 1,200 rpm and regularly “cleared” the engine by increasing engine power. After touchdown, the pilot pushed carburetor heat off and applied full throttle to take off again, adding that the engine felt and sounded like it was producing full power. About 40 to 50 ft above ground level, the engine lost power and he slipped the airplane to lose altitude, landing on the remaining runway. During the landing roll, the pilot applied brakes to prevent a runway overrun, and the airplane nosed over and came to rest inverted.

Impact damage to the intake manifold assembly precluded an engine run. Examination of the engine was performed by a mechanic following recovery of the airplane. The fuel strainer and carburetor bowl were full of blue-colored liquid consistent with 100 low lead aviation fuel; slight particulate contamination was noted in the carburetor bowl. No blockage or obstructions of the air induction, exhaust, fuel vent, or fuel supply system from each tank to the engine through the fuel selector valve in the left and right positions was noted. Compression was established for each cylinder, and examination with a lighted borescope revealed no anomalies, with the exception of the No. 2 exhaust valve, which exhibited some discoloration. The left and right magnetos were timed 27.5° and 20.0° before top center (BTC), respectively (specification for left and right are 30° BTC and 28° BTC, respectively). All spark plugs exhibited evidence of a rich fuel/air ratio. Carburetor heat control continuity was confirmed from the cockpit to the airbox. The carburetor heat was in the off position; impact damage to the door at the airbox precluded activation from the cockpit.

At 1156, the weather reported at Columbia Metropolitan Airport (CAE), about 16 miles west of the accident site, included a temperature of 32°C and a dewpoint of 22°C. The calculated relative humidity at this temperature and dewpoint was about 58 percent. Review of the icing probability chart contained within Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35 revealed the atmospheric conditions at the time of the accident were "conducive to icing at glide [idle] and cruise power."

The Federal Aviation Administration (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 the closed-throttle operation. The publication also stated that, periodically, the throttle should be opened smoothly for a few seconds to keep the engine sufficiently warm to prevent carburetor icing.