Poor maintenance blamed for engine failure

This April 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.

Aircraft: Cessna 152. Injuries: None. Location: Avon Park, Fla. Aircraft damage: Substantial.

What reportedly happened: About a week before the accident, the pilot noticed fuel leaking from the airplane’s carburetor. He informed a mechanic, who assured him that the airplane was fine and that the leak could be stopped by knocking a screwdriver against the carburetor. The pilot did as instructed, and the leak stopped.

The day before the accident, the pilot asked the mechanic whether any maintenance was conducted on the carburetor, and the mechanic informed him that no maintenance was conducted, because it was not necessary. The pilot then rented the airplane and conducted an uneventful flight to his destination.

The next day, during the cruise portion of the return flight, the engine rpm suddenly decreased below 2,000 rpm. The pilot attempted to restore power by adjusting the mixture and carburetor heat controls, and verified that the ignition switch and master switches were appropriately set. The rpm continued to decrease, and about 30 seconds after the onset of the rpm drop, the engine stopped producing power. During the forced landing on a road the airplane’s left wing hit a fence post.

Meteorological conditions recorded about 25 miles from the accident location indicated the conditions were conducive to carburetor icing with the engine at glide power, but not at cruise power. On-scene examination of the airplane revealed that sufficient, uncontaminated fuel was available, and that the fuel selector valve was properly set. The engine was test run on the airplane, at various rpm settings, with no anomalies noted. The carburetor was removed and further examined. When fuel was introduced via the fuel inlet, the carburetor immediately started flooding and leaking from the venturi, which was consistent with an open float valve. Further examination and teardown revealed multiple anomalies, including internal contamination and corrosion, excessive wear, incorrect parts, incorrectly installed parts, and a damaged float assembly. Some of the internal contaminants floated, and some sank in the fuel, which allowed for the possibility that the contaminants could prevent full closure of the float valve. The excessive wear and twisted float assembly could also prevent proper float operation. Improper float valve or float operation could result in either intermittent abnormal engine operation or a complete loss of power.

Probable cause: The operator’s failure to correct known deficiencies with the carburetor, which resulted in a complete loss of engine power and subsequent forced landing by the pilot. Also causal was the operator’s decision to rent the airplane in an unairworthy condition.

For more information: NTSB.gov. NTSB Identification: ERA10LA235




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