Accident Details
On August 14, 2018, at about 1030 mountain daylight time, a Cessna 140 airplane, registration N89093, sustained substantial damage during a forced landing in the Snake River near Marsing, Idaho. The pilot and passenger were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Sequence of Events
The pilot reported that after entering the traffic pattern at Sunrise Skypark Airport (ID40), he reduced engine power, applied carburetor heat, and executed a low pass over runway 12. As the airplane approached midfield at approximately 60 ft above ground level, he advanced the throttle, but the engine did not respond. The pilot switched fuel tanks from left to right. With insufficient runway remaining to land, he initiated a forced landing to the shallow side of the Snake River, which paralleled the runway. During the landing, the airplane impacted water and came to rest upright, partially submerged. The firewall and lower fuselage were substantially damaged.
Examination of the Wreckage
Post-accident examination revealed that all engine accessories remained attached. Due to impact damage to the airframe fuel strainer, an external fuel source was attached to the carburetor inlet fuel line for an engine test run. Despite multiple attempts, the engine would not start. The airbox and carburetor were subsequently removed, and the carburetor was partially disassembled. An orange residue consistent with rust was observed in the float bowl, along with residual water. The float bowl and mixture metering sleeve were cleaned using carburetor cleaner, and the carburetor was reassembled. The engine then started, after multiple attempts, at a power setting of 1,800 rpm or more. When engine rpm was reduced below 1,300 rpm, the engine lost power. After restarting at 1,700 rpm, a magneto check showed a decrease of 100 rpm for both magnetos. The maximum rpm obtained during the engine run was 2,300 rpm. The carburetor was removed and retained for further examination.
Carburetor Inspection
The carburetor was examined at the manufacturer’s facility under the supervision of a Federal Aviation Administration inspector. The inspector reported that the throttle shaft was loose in its bushings or mounting to the casting. Movement of the throttle indicated that the accelerator pump was not sealing against the wall of its chamber, which would not provide fuel required to increase power with throttle movement. When the carburetor was installed on a 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 were present, and at idle ranges, fuel flows were significantly out of specification. Removal of the idle tube revealed significant corrosion and contaminants in that area.
Maintenance Records
Airframe and engine logbooks contained no specific entries related to an overhaul or maintenance on the carburetor.