What happened
Prior to a cross-county flight, the pilot filled the inboard fuel tanks of the multiengine airplane to their maximum capacity. While approaching the destination airport, the pilot received instructions from air traffic control to execute a right turn for a visual approach. During this maneuver, the pilot indicated that an emergency landing on a highway might be necessary. The aircraft subsequently struck a marsh approximately 15 miles from its intended destination.
Data retrieved from an onboard engine monitor showed that the right engine experienced a momentary loss and recovery of power before failing completely. Upon inspection of the wreckage, investigators found that the left propeller had been feathered, while the right propeller remained in its normal operating position. Although the left wing tanks were depleted, the right wing tanks contained enough fuel to finish the flight, though the right main tank was at a low level due to consumption during the trip.
Findings
Investigation of the right wing main fuel tank revealed that the tank lacked a necessary flapper valve on the baffle near the fuel pickup. This valve is essential for keeping fuel near the pickup point and preventing it from shifting toward the wingtip. Evidence suggests that during the right turn, the absence of this valve allowed fuel to move outboard, causing fuel starvation to the right engine.
While the aircraft's maintenance records did not explicitly document the replacement of the right main fuel tank bladder, the age of the component indicated a prior replacement. It is believed that maintenance staff failed to reinstall the flapper valve during that previous installation. Furthermore, toxicology results indicated the pilot's blood alcohol level was likely between 0.077 gm/dl and 0.177 gm/dl, a level considered impairing. This impairment likely caused the pilot to incorrectly feather the functioning left engine instead of the failed right engine, making it impossible to maintain flight altitude.