ERA21LA391

The pilot reported that, while the airplane was at an altitude of 3,500 ft, the engine lost total power. He attempted to regain engine power by adjusting the throttle, mixture control, fuel valve controls, and carburetor heat; however, the engine would not restart. As the pilot set up an approach to a nearby airstrip, he determined that the airplane would not reach the runway and performed a forced landing into trees, resulting in substantial damage to the fuselage and wings. Postaccident examination of the engine revealed that the carburetor’s rotating mixture actuating rod was difficult to rotate, and binding occurred as the actuating rod was rotated by hand. Upon disassembly of the carburetor, the mixture control actuating rod and the metering needle, which is connected to the inner end of the rod, were found bent. No other damage to the carburetor was found. Because these components are largely or entirely internal to the carburetor, the bending of actuating rod and the metering needle was likely not a result of impact damage. The investigation was unable to determine how or when the carburetor components became bent. Although the bends in the actuating rod and metering needle would not have prevented the mixture control from operating, the bends would have changed how the mixture setting in the carburetor responded to the mixture control lever in the cockpit. If the cockpit control was moved toward the cutoff position, the metering needle might not have performed as expected and might have moved into the cutoff position before or after the cockpit control reached its expected cutoff position. Likewise, with the cockpit control in the normal full rich position, the metering needle might have been in a position that was either more or less than full rich. Therefore, the bent components likely resulted in a mixture setting that was not expected for any given cockpit mixture control setting. The investigation could not determine whether the mixture would have been too lean (less fuel) or too rich (more fuel), either of which could have resulted in the engine not producing power. Four of the cylinders’ spark plugs had black-colored deposits on their electrodes, consistent with a rich mixture condition. Two spark plugs had gray-colored deposits, consistent with a normal mixture condition. The remaining three spark plugs were oil soaked, masking their electrode color, but these spark plugs would generally be more consistent with a rich mixture condition rather than a lean condition.

On September 30, 2021, about 1330 eastern daylight time, a Boeing E75, N1654M, was substantially damaged when it was involved in an accident near Nicholson, Pennsylvania. The pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, while the airplane was at an altitude of 3,500 ft, the engine suddenly lost total power. He adjusted the throttle, mixture control, fuel valve controls, and carburetor heat, but the engine would not restart. Shortly afterward, the pilot noticed a strong smell of fuel. He then flew the airplane toward a nearby private airstrip. While setting up an approach to the runway, the pilot determined that the airplane would not reach the airstrip and performed a forced landing into trees that bordered the airport property, which resulted in substantial damage to the fuselage and wings. Postaccident examination of the airplane found that the engine separated from the fuselage during the accident sequence and that fuel had been draining from the fuel line for “some time” after the accident occurred. A subsequent examination of the engine revealed that the carburetor’s rotating mixture actuating rod was difficult to rotate, and binding occurred as the actuating rod was rotated by hand. (The cockpit mixture control lever, through a linkage of push-pull tubes and control arms, rotates the mixture actuating rod.) The carburetor was then disassembled, and the actuating rod and the metering needle connected to the inner end of the rod were found bent, as shown in the figure below. (The metering needle attaches to an offset pin at the inner end of the actuating rod. As the rod rotates, the metering needle moves up or down [out of or into its seat] to control the amount of fuel that flows through the carburetor, setting the mixture.) Figure. - Mixture actuating rod and metering needle. The carburetor was otherwise undamaged. No impact marks, deformation, or other damage was found to the housing or bushings that surround the actuating rod and the seat for the metering needle. Other than the mixture actuating rod and the metering needle, no preimpact anomalies were found with the engine or the airframe fuel system components that would have precluded normal operation. The front spark plugs were removed from the cylinders. Two had gray-colored electrodes, four had black-colored electrodes, and three of the electrodes were oil soaked. A review of the maintenance records revealed no entries related to the carburetor or its controls during the preceding 4 years. During that time, the engine accumulated 81 hours total time.