Accident Narrative
Witnesses reported that the accident airplane had just dropped a banner and was being maneuvered from base to final approach for a landing on runway 06. The pilot made a radio transmission stating that aileron control had been lost. The airplane was observed at an altitude of approximately 200 to 300 feet, in about a 30-degree left bank. The bank angle continued to increase as the airplane descended, disappearing from sight behind the treeline. The airplane impacted the ground nose-down, in a near vertical attitude, and came to rest suspended by trees.
Aircraft Examination
Examination of the airplane revealed that the aileron control cable had separated between the bell crank in the left wing and the vicinity of the right upper doorpost pulley on its way to the control yoke. Corrosion was present on the upper left and right doorpost pulley bearings, the lower right doorpost pulley bearing, the bulkhead assembly-rear doorpost channel near the upper pulley, and the inner surface of the wing skins and ribs of both the left and right wings. The right wing forward flap cable was found to have separated about 27 inches from the bellcrank in the right wing. Corrosion was observed at the flap attachment rods, and both the left and right attachment rods were bent.
Laboratory Findings
Sections of the broken flap and aileron cables were examined at the NTSB Materials Laboratory in Washington, D.C. The examination revealed that the wire rope of the flap cable had separated with almost all of the wires broken within a 0.5-inch axial length. There was minor unraveling of the strands adjacent to the separation, but no unraveling of the individual wires within strands. Detailed examination with a bench binocular microscope revealed extensive corrosion damage at the broken ends, with many of the individual wires corroded all of the way through. Dark deposits that appeared to be a mixture of oxidation debris and dried grease were noted within about 1 inch of the broken ends. The wire rope of the aileron cable had separated with almost all of the wires broken within a 0.5-inch axial length. There was some unraveling of the strands as well as the individual wires within strands adjacent to the separation. Detailed examination with a bench binocular microscope revealed extensive corrosion damage at the broken ends, with many of the individual wires corroded all of the way through. Dark and rust-colored oxidation deposits were noted within about 1.5 inches of the broken ends.