ERA21LA166

The pilot reported that while in cruise flight, the engine ran rough then smoothed right out. The pilot elected to return to the airport and the engine roughness increased. He applied carburetor heat and cycled the magnetos. When operating on the left magneto the engine stopped, then it started again when the selector was placed back to the BOTH position. The airplane was shaking, and the pilot was unable to maintain altitude so he elected to perform a precautionary landing on a dirt road. The left wing stuck tree branches, and the airplane spun around and came to rest submerged in a canal adjacent to the road. Postaccident examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Although the weather conditions at the time of the accident were conducive to the accumulation of carburetor icing at glide power, the pilot reported that he used carburetor heat, which would have prevented the accumulation of ice. The reason for the total loss of engine power could not be determined based on available information.

On March 30, 2021, about 1057 eastern daylight time, a Jabiru USA Sport Aircraft J250-SP, N236X, was substantially damaged when it was involved in an accident near Fort Pierce, Florida. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, about 10 minutes after takeoff, while in cruise flight at 2,500 ft mean sea level, the engine “got rough, then smoothed right out.” He made a 180° turn to return to the airport and the engine “got very rough.” He turned the carburetor heat ON and checked the magnetos. When he switched from BOTH to the right magneto, there was no change. When he switched from BOTH to the left magneto the engine stopped, but then started again when he switched back to BOTH. The airplane was shaking and he was unable to maintain altitude so he elected to make a precautionary landing on a dirt road alongside a canal. As the airplane approached the road, the pilot maneuvered to avoid large trees; however, during the landing the left wing struck tree branches and the airplane spun around coming to rest in the tidal canal. According to the Federal Aviation Administration (FAA) inspector who responded to the accident site, the airplane’s left wing was mostly separated, and the entire airplane was submerged. A detailed engine examination supervised by the FAA inspector revealed no anomalies. The engine’s crankshaft was rotated by hand, and internal and valve train continuity was established. Fuel was present throughout the fuel system, carburetor, and fuel filters, and the fuel was absent of debris. A small amount of water was present in the carburetor. Both magnetos produced spark. At 1053, the weather reported at St. Lucie County International Airport, about 9 miles east of the accident site, included a temperature of 28°C and a dew point of 19°C. The calculated relative humidity at this temperature and dewpoint was 94%. Review of the icing probability chart contained in Federal Aviation Administration (FAA) Special Airworthiness Information Bulletin CE-09-35 revealed that the weather conditions at the time of the accident were "conducive to serious icing at glide [idle] power."