Cessna 172 N7748U accident near Salmon, Idaho

Probable cause

A loss of engine power due to water in the fuel system. Contributing to the accident was an inadequate preflight inspection that failed to eliminate water from the fuel system.

NTSB analysis

The flight instructor stated that during an instructional flight, he configured the airplane for a simulated engine failure by applying carburetor heat and decreasing the engine power. The student pilot followed emergency procedures, used the checklist, and prepared to land. When the carburetor heat control was pushed back in and the throttle was advanced, the engine suddenly lost power. The flight instructor tried restarting the engine to no avail and initiated a forced landing, during which the airplane struck a fence.

Postaccident examination of the airplane revealed that the original inline fuel strainer was replaced with an aftermarket inline fuel strainer with a manual sump valve on the strainer bowl. The inline fuel strainer drain knob from the original fuel strainer was removed from the instrument panel. The fuel strainer was drained and found to be filled about 3/4 with water. The student pilot stated that the only sumps that were drained during the preflight inspection were the wing tank sumps. He further stated that he did not know about the fuel strainer having a sump and that the flight instructor never told him about it. The flight instructor stated that he performed a preflight inspection after the student pilot had drained the wing tanks and fuel strainer sumps. He further stated that he thought the student pilot found some water in the left wing tank but did not drain the fuel strainer. It is likely that the engine lost power due to water in the inline fuel strainer, which led to the forced landing.

Text from the NTSB. Open the NTSB docket for WPR16LA133 for the full record.