What happened
While performing a crosswind leg following takeoff, the pilot announced that the aircraft had lost an engine and intended to return to the airport. During a left turn back toward the airport, the aircraft rolled inverted to the left and entered a nose-down descent until impact.
The investigation
An examination of the left engine carburetor revealed an extra needle valve that was loose inside the float bowl. While another needle valve and seat assembly was correctly installed in the carburetor, investigators found numerous smooth, bright spots of wear on the bottom surface of the grainy textured interior of the float bowl. Additionally, the area surrounding the fuel mixture metering assembly port had been polished, allowing the needle valve to be inserted into the port.
Maintenance records showed that new engines had been installed on October 30, 1979. Although witnesses and maintenance records indicated there had been power problems with the left engine, no documentation existed to show that the carburetor float bowl had been removed for service since the initial installation of the engines on the aircraft.