American Champion Aircraft 7GCBC N255SF accident near Lufkin, Texas

Probable cause

The restricted movement of the carburetor’s forked needle valve within its seat due to the mechanic’s misadjustment of the valve clip forks, which resulted in fuel starvation.

NTSB analysis

The pilot was flying a pipeline patrol flight about 500 feet above ground level. About 6 miles south of the destination, the engine abruptly lost power. The pilot observed that both fuel tanks contained a usable level of fuel. Additionally, he saw no obvious issues with the mixture setting, carburetor heat, magnetos, throttle position, and fuel shutoff valve. The pilot landed the airplane in a field with high vegetation, which resulted in strut damage.

The pilot did not report any fuel or oil leaks. During a postaccident examination, the engine was intermittently operational. The engine would produce power when the carburetor was "tapped" after the engine stopped. A carburetor examination revealed that the accelerator pump was operational and that the fuel screens were clear of debris. However, the forked needle valve's movement within its seat was restricted. The valve clip forks were observed resting on the valve seat when the carburetor's throttle body was inverted. The carburetor maintenance manual specified that a minimum clearance must exist between the forked valve clip and the valve seat. It is likely that the restricted movement of the carburetor's forked needle valve resulted from the mechanic's misadjustment of the valve clip forks, which subsequently caused the engine to lose power due to fuel starvation.

Text from the NTSB. Open the NTSB docket for CEN13LA406 for the full record.