Primary finding
Probable cause
The pilot’s adjustment of the carburetor to an incorrect setting, which resulted in partial loss of engine power during takeoff.
Investigator assessment
Analysis narrative
The pilot of the experimental amateur-built airplane was departing from his private dirt strip when the accident occurred. The airplane exhibited a partial loss of engine power when it was about halfway down the runway. The pilot elected to proceed with the takeoff due to an irrigation canal at the end of the runway. The airplane would not gain altitude and subsequently struck two fences before nosing over and coming to rest inverted in a nearby yard. Postaccident examination of the engine revealed that one of the two piston-type carburetors had the retaining clip for the jet needle set to the leanest position. The other carburetor was set to the engine manufacturer’s specified position. It is likely that the overly lean setting in one of the carburetors caused the carburetors not to be synchronized, which resulted in the partial loss of engine power during takeoff. According to the pilot, he adjusted the carburetor’s retaining clip to lower the cylinder temperature while he was flying in a different state and did not notice any loss of engine performance. However, this was his first attempted takeoff in Wyoming, that was located at a high elevation.
Source record
Factual narrative
On May 10, 2024, about 1030 mountain daylight time, an experimental amateur-built Kitfox airplane, N605GK, was substantially damaged when it was involved in an accident near Powell, Wyoming. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that while departing from his private dirt strip, about halfway down the runway, the airplane’s engine began to sputter and lost partial power. He confirmed the boost pump was on and proceeded with the takeoff since there was an irrigation canal at the end of the runway. The airplane would not gain altitude and subsequently struck two fences before nosing over and coming to rest inverted in a neighbor’s yard. The right wing sustained substantial damage during the accident sequence. The airframe was not available for examination because it was inadvertently sold. A postaccident examination of the Rotax 582 engine revealed that it was equipped with two piston-type carburetors. On the carburetor near the magneto (MAG carburetor), the retaining clip for the jet needle was noted have been set to the No. 1 position (most lean). On the carburetor near the gear box/propeller (power take-off carburetor), the retaining clip for the jet needle was set to the No. 3 position. The jet needles had 4 positions in which the retaining clip would seat. The No. 1 position was near the top of the needle and was the leanest setting; the subsequent 3 positions were equally spaced below the No. 1 position, ending with the No. 4 position at the lowest position. The No. 3 position of the retaining clip for the jet needle was the position set when manufactured, according to the representative of the engine manufacturer. The Rotax Maintenance Manual specified that, when installing the carburetor, press the needle clip in the same position as recorded. The Maintenance Manual Line for the engine states, “the needle jet and jet needle must only be exchanged by a mechanic with experience on two-stroke engines and in accordance with the Maintenance Manual Heavy.” Furthermore, the Illustrated Parts Catalog for the engine listed the carburetor calibration as needle position 3. Both carburetor pistons slides were observed to have scoring marks consistent with the carburetors not being synchronized. Additionally, the engine’s maintenance manual lists a rough running engine as being caused by incorrect synchronization of the carburetors. According to the pilot, he adjusted the carburetor retaining clip to lower the front cylinder temperature that was running high. The adjustment slightly lowered the cylinder temperature, and he noticed no performance loss while flying multiple flights in Arizona. The takeoff on the accident flight was the first one attempted in Wyoming at an elevation of about 4,400 ft.