What happened
During the descent phase of flight, the pilot was maneuvering the aircraft to avoid inclement weather when they observed irregular oscillations in the manifold pressure and fuel flow of the left engine. Although the left propeller remained in operation, the pilot decided against feathering the propeller at that time. As the aircraft became unable to sustain its altitude, the crew deployed the landing gear and performed an emergency ditching into a swamp.
Findings
An inspection of the left fuel tank identified significant wear on the fuel float arms and the actuators for the fuel float valves. This mechanical degradation permitted unmetered air to enter the fuel delivery lines. Additionally, investigators found that one of the left fuel valves was prone to jamming in the open position, which could cause the fuel pickup to unport and introduce further air into the fuel system.