On April 11, 2019, about 1430 eastern daylight time, a Cessna 150G, N3795J, was substantially damaged when it was involved in an accident near Fulton, New York. The private pilot received serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that the airplane was last flown on July 21, 2018. The airplane had a supplemental type certificate for the use of automotive fuel, but the pilot kept it stored with 100LL aviation fuel. Before the accident flight, he added fewer than 5 gallons of 100LL aviation fuel to top off both tanks before departure. The 2-hour flight was uneventful, and he reduced engine power for the descent, but it remained above 2,000 rpm. Just after turning onto the base leg of the traffic pattern for landing, the pilot applied the carburetor heat as he prepared to reduce the engine power below 2,000 rpm. As soon as he applied the carburetor heat, the engine “faltered” and lost partial power. The engine noise decreased but did not cease. He then pushed the carburetor heat fully off, and the engine seemed to regain some, but not all, power. He then reapplied the carburetor heat and the engine lost all power. The pilot performed a forced landing to a road in a populated area about 1.3 nautical miles from the end of the runway. During landing, the right wing impacted a utility pole, and the airplane came to rest inverted with both wings partially separated from the fuselage.

Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed substantial damage to both wings and the fuselage. First responders observed fuel on the roadway and leaking from the airplane upon their arrival. The fuel selector was found in the “on” position.

Engine crankshaft, valvetrain, and accessory gear continuity were confirmed when the crankshaft was rotated by hand. The exhaust, induction, and carburetor heat exchanger components were intact and showed no indication of leaks. Due to impact damage, the carburetor heat cable could not be tested; however, the control arm on the induction airbox operated normally. Both magnetos produced spark on all towers when rotated, and the ignition harness remained intact, with some damage noted to the Nos. 1 and 3 leads at the top spark plug ends. The spark plugs on cylinder Nos. 1 and 3 were oil-soaked. There was no sooting observed on any of the spark plugs and all insulators were appeared white in color. The carburetor floats, inlet valve jets, and accelerator pump were intact. The inlet screen was clear of any contaminants. The inlet valve functioned properly when air pressure was applied to the fuel inlet while float assembly was exercised up and down.   A computer model of the weather conditions in the area of the accident site around the accident time indicated conditions favorable to the development of carburetor icing from the surface to 13,000 ft mean sea level at glide and cruise power settings.

According to FAA Special Airworthiness Information Bulletin CE-09-35:

Pilots should be aware that carburetor icing doesn’t just occur in freezing conditions, it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, (Venturi Effect) causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes. In both types, usually there will be a roughness in engine operation…

To recognize carburetor icing, the warning signs are: • A drop in rpm in fixed pitch propeller airplanes. • A drop in manifold pressure in constant speed propeller airplanes. • In both types, usually there will be a roughness in engine operation. The pilot should respond to carburetor icing by applying full carburetor heat immediately. The engine may run rough initially for short time while ice melts.