Stuck valve leads to power loss

Aircraft: Cessna 180. Injuries: None. Location: Omaha, Neb. Aircraft damage: Substantial.

What reportedly happened: The airplane was on final approach and a half-mile from the runway when the engine lost power. It came down in trees short of the runway.

During the post-accident testing of the engine, it lost power when the throttle was moved quickly from a low to high power setting. The power loss became more pronounced as the engine got warmer. The carburetor was removed from the engine and inspected. A roughness was felt in the accelerator pump while manually moving the control at the carburetor, and very little fuel flow came from the accelerator pump.

The carburetor was disassembled and all check valves, ports and vents, the venturi, nozzle bleed holes, carburetor bowl vent channels, and float assembly were cleaned. After reassembly, a much higher fuel output was achieved. The inspectors concluded that the carburetor acceleration pump or the check valve below it had become stuck, resulting in an improper fuel mixture when the pilot attempted to add power, causing the engine to lose power.

Probable cause: A loss of engine power due to a stuck check valve in the carburetor acceleration pump, resulting in an improper fuel mixture when the pilot attempted to add power.

NTSB Identification: CEN11LA089

This December 2010 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

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