Incident Overview
On August 22, 2020, at approximately 1151 central daylight time, a Cessna 180 airplane, registration N7620A, was substantially damaged during a forced landing near St. Louis, Missouri. The pilot, who was the sole occupant, sustained serious injuries. The flight was being conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Account
According to the pilot, while en route about five minutes after departure, he heard a loud "pop" followed by a sudden loss of engine power. He initiated a forced landing toward a lacrosse field surrounded by residential areas. The airplane impacted terrain short of the intended field in a nose-low attitude, resulting in damage to both wings and the fuselage.
Postaccident Examination
Examination of the flight controls, fuel system, and muffler revealed no anomalies. Fuel from the gascolator appeared normal in color and smell, with no visible contamination. The engine crankshaft was rotated, and all cylinders showed evidence of compression. No issues were found with the magnetos or spark plugs.
The carburetor mixture control cable was discovered disconnected from the control lever at the carburetor. The attachment hardware—comprising a bolt, nut, and washer stack—remained attached to the carburetor. The carburetor mixture control lever, which was not spring-loaded, was found in the cut-off position. The cockpit mixture control lever was approximately 2 inches from the full rich position.
Carburetor and Cable Analysis
The carburetor was examined at a repair facility, and no anomalies that could have led to a fuel stoppage were observed. A section of the carburetor mixture cable and its attachment hardware were analyzed at the National Transportation Safety Board (NTSB) Materials Laboratory. The central wire of the mixture control cable exhibited multiple flat areas around its outer diameter. The attachment bolt showed bands of wear on its outer diameter consistent with rub damage from the washers, and the washer faces had circumferential wear marks.
Maintenance Manual Reference
The engine maintenance manual specified that the carburetor mixture control wire should be bent 90 degrees after threading through the bolt hole to help secure the wire. Examination of the wire end revealed no evidence of a kink or sharp bend.