Cessna 140 N89093 accident near Marsing, Idaho

Probable cause

The loss of engine power during a low pass as a result of a blockage of the carburetor idle chambers which led to a forced landing in a river.

NTSB analysis

During a low pass over the runway, the pilot advanced the throttle, but the engine failed to respond. After switching fuel tanks, the pilot initiated a forced landing to a shallow part of a river that paralleled the runway. The airplane came to rest upright in the river, partially submerged, and sustained substantial damage to the lower fuselage and firewall.

Postaccident examination of the airplane revealed that the engine initially would not run. The carburetor was removed, partially disassembled, and examined. Evidence of corrosion was observed in the float bowl. The carburetor bowl was cleaned internally, reassembled, and reinstalled on the engine. Additional attempts to run the engine revealed that the engine would not run at power settings below 1,300 rpm.

Subsequent examination of the carburetor revealed that the throttle shaft was loose in its bushings or mounting to the casting. When the carburetor was installed on a fuel flow bench, immediate leaks were noted audibly, one at the throttle shaft seals and one in the area of the accelerator pump. Indications of blockage in the idle chambers of the carburetor were present, and at idle ranges, the fuel flows were significantly out of specification which likely led to the loss of engine power. Removal of the idle tube showed significant corrosion and contaminants in that area. The source of contaminants was not determined.

Text from the NTSB. Open the NTSB docket for WPR18LA224 for the full record.