AMERICAN CHAMPION AIRCRAFT 7GCBC near Lufkin, TX — 2013-07-03

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 narrative

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.

Analysis

Primary failure mode

Engine power loss

First missed decision gate

Pilot could have checked carburetor settings before flight to prevent engine power loss.

NTSB coding

• Loss of engine power (total) · Maneuvering-low-alt flying
• Maintenance

Evidence available

• Photos
• 6 docket documents

Docket documents6

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Overhauler's Teardown Statementinterview
• Communication Summary - Operator Findingsother
• Photo 1 - View of the float, clip, fork, and valve seatphotos
• Photo 2 - View of the inlet screenphotos
• Photo 3 - View of the accelerator pump screenphotos

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