The pilot departed from Mid-Valley Dusters Inc. Airport (43TX) in Alamo, Texas, on the last flight of the day and noticed an abnormal sound from the engine as the Aero Commander S2R reached an altitude of about 25 feet above ground level.
He elected to make an immediate precautionary landing rather than risk having the engine lose power over obstacles farther along the departure path, including a high traffic highway and a low power line.
During the landing roll, both wings sustained substantial damage due to impact with trees.
Examination of engine cylinders, spark plugs, induction tubes, exhaust stacks, and magnetos did not reveal any anomalies that would have precluded normal operation. The fuel tank sumps, header tank sumps, and manual auxiliary fuel pump sumps were drained with no contamination noted. The rear carburetor bowl drain was removed, and a small amount of water-contaminated fuel was observed.
The engine was started and accelerated to 1,800 rpm with no anomalies noted. A normal rpm drop occurred when the magnetos were checked, and the propeller cycled normally. No smoke was produced when the engine was returned to idle power, which was consistent with normal functioning of the blower seal.
Probable Cause: The partial loss of engine power due to water-contaminated fuel.
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This February 2021 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.
I don’t know how water can get into a carburetor with a functional gascolator, which should catch any water in the fuel lines.
A carb does have a bowl vent, but has a filter in it… Maybe atmospheric moisture was pulled into to bowl as the carb cooled.?
I drain and flush the carb bowl at every annual and I’ve never found water, but usually find some fine grit.