Cessna U206G N891LL accident near Cave-In-Rock, Illinois

Probable cause

A total loss of engine power due to air entering the fuel system for reasons that could not be determined based on available information. Contributing to the accident was the pilot’s inability to restart the engine due to the check valve assembly design.

NTSB analysis

The airline transport pilot and camera operator were conducting an aerial mapping flight. While level at 3,500 ft above ground level, the turbo propeller-equipped airplane experienced a total loss of engine power. The pilot attempted to restart the engine three times without success. During the subsequent forced landing, the airplane struck a berm, which damaged both wings.

Examination of the engine revealed that fuel would not flow to the fuel nozzle until air pressure was bled upstream of the check valve assembly, located between the engine fuel control and the fuel nozzle. After the air pressure was bled and the fuel pump purged, normal fuel flow resumed, indicating that air had entered the fuel system. Because of the check valve assembly design, an in-flight engine restart was not possible after air entered the fuel line, and there was no procedure to clear air from the fuel line while in flight. Examination of the engine and fuel system could not establish a reason for air entering the fuel line.

Text from the NTSB. Open the NTSB docket for CEN16LA335 for the full record.