St Louis, MO, USA
N7620A
Cessna 180
While in cruise flight, the pilot reported hearing a loud “pop,” and the engine suddenly lost power. The pilot executed a forced landing toward a lacrosse field surrounded by residences. The airplane impacted terrain in a nose-down attitude, which substantially damaged both wings and seriously injured the pilot. A postaccident examination revealed that the carburetor mixture control cable was disconnected from the carburetor control lever at the carburetor, with the attachment hardware (bolt, nut, and washer stack) still attached to the carburetor. No other anomalies were found that would have precluded normal operation. Laboratory analysis of the mixture control cable and attachment hardware (bolt, nut, and washer stack) determined that the hardware was used repeatedly in numerous configurations, and the cable did not have a kink at the end indicating it had not been bent. The maintenance manual specified that the cable was to be bent 90 degrees after being threaded through the bolt hole to help secure the cable, and not doing so likely contributed to the cable becoming disconnected from the carburetor control lever inflight.
On August 22, 2020, about 1151 central daylight time, a Cessna 180 airplane, N7620A, was substantially damaged when it was involved in an accident near St. Louis, Missouri. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that while en route about 5 minutes after takeoff, he heard a loud "pop" followed by a sudden loss of engine power. The pilot executed a forced landing toward a lacrosse field surrounded by residences. The airplane subsequently impacted terrain short of the field in a nose-low attitude, which resulted in damage to both wings and fuselage. Postaccident examination of the flight controls, fuel system, and muffler revealed no anomalies. Fuel collected from the gascolator was observed to have normal color and smell, with no signs of visual contamination. The engine crankshaft was rotated, and all cylinders showed evidence of compression. No anomalies were noticed with the magnetos or spark plugs. The carburetor mixture control cable was found disconnected from the control lever at the carburetor, with the attachment hardware (bolt, nut, and washer stack) still attached to the carburetor. The carburetor mixture control lever, which was not spring loaded toward a particular direction, was found at the cut-off position. The cockpit mixture control lever was about 2 inches from the full rich position. The carburetor was examined at a repair facility. No anomalies were observed that would have led to a fuel stoppage of the engine. A section of the carburetor mixture cable and attachment hardware were examined at the National Transportation Safety Board (NTSB) Materials Laboratory. The central wire of the mixture control cable had multiple flat areas around the outer diameter. The attachment hardware bolt had bands of wear on the outer diameter consistent with rub damage from the washers, and the washer faces had circumferential wear marks consistent with rub damage. The engine maintenance manual specified that the carburetor mixture control wire was to be bent 90º after being threaded through the bolt hole to help secure the wire. No evidence of a kink or sharp bend was observed at the wire end.
A total loss of engine power due to improper maintenance of the mixture control cable and attachment hardware, which led to a forced landing into a congested area.
Source: NTSB Aviation Accident Database
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