CEN25LA054

The pilot was conducting a personal flight when the airplane had a partial loss of engine power shortly after takeoff about 500 ft above the departure end of the runway. The pilot reported that the engine appeared to be running at idle power and he was unable to maintain altitude. The pilot completed a forced landing into a nearby grass field, during which the nose landing gear separated from the forward fuselage. The airplane’s left wing leading edge was substantially damaged during the forced landing. Examination of the engine did not reveal any evidence of a mechanical failure that would prevent normal operation. Visual examination of the engine’s exterior revealed that all four engine cylinders had evidence of mud dauber nests within their respective cooling fins. Additionally, a roughly 1.5-inch diameter mud dauber nest was found in the airbox between the air filter and the throat of the carburetor. Additionally, dirt with the same color as the mud dauber nest was observed within the carburetor throat and on the clean side of the air filter. The recovered mud dauber nest exhibited impressions consistent with the spacing of the wire coil that supported the flexible ducting associated with the carburetor heat system. As such, the mud dauber nest would not be visible during a preflight inspection. The flexible ducting also contained various-sized fragments of mud dauber nest debris. Based on the available evidence, it is likely the mud dauber nest became dislodged shortly after takeoff and partially obstructed the induction airflow into the carburetor, which resulted in a partial loss of engine power.

On December 1, 2024, about 1438 central daylight time, an American Aviation AA-1B airplane, N6242L, sustained substantial damage when it was involved in an accident near Brenham, Texas. The pilot and his passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that there was a partial loss of engine power shortly after takeoff from runway 34 at Brenham Municipal Airport (11R), Brenham, Texas. The partial loss of engine power occurred about 500 ft above the ground as the airplane flew over the departure end of the runway. The pilot reported that the engine appeared to be running at idle power and he was unable to maintain altitude, so he conducted a forced landing into a grass field north of the airport. The airplane’s nose landing gear separated during the forced landing. The airplane’s left wing leading edge was substantially damaged during the forced landing. The left wing exhibited a large semicircular impact likely due to a collision with the separated nose gear and/or with an anthill in the grass field. However, the leading-edge damage did not exhibit evidence of tire rubber transfer or scratching, nor did it contain anything resembling dirt/sand. Examination of the engine did not reveal any evidence of a mechanical failure that would prevent normal operation. A visual examination of the engine’s exterior revealed that all four engine cylinders had evidence of mud dauber nests within their respective cooling fins. Additionally, a roughly 1.5-inch diameter mud dauber nest was found in the airbox between the air filter and the throat of the carburetor, as shown in figure 1. Additionally, dirt with the same color as the mud dauber nest was observed within the carburetor throat and on the clean side of the air filter. The recovered mud dauber nest exhibited impressions consistent with the spacing of the wire coil that supported the flexible ducting associated with the carburetor heat system. The flexible ducting also contained various-sized fragments of mud dauber nest debris. The airplane had flown 4.7 hours since the last annual inspection that was completed on November 17, 2024. The air filter was replaced during the annual inspection. At the time of the accident, the engine had accumulated 531.7 hours since the last major overhaul that was completed on May 1, 1999. Figure 1. Mud dauber nest found in the airbox between the air filter and the throat of the carburetor. Red arrows point to the mud dauber nest. (Photos courtesy of Lycoming Engines and edited by NTSB)