Incident Overview
On August 1, 2010, at approximately 1200 central daylight time, a Piper PA-32R-301T airplane, registration N4184X, experienced a complete loss of aileron control while approaching Mount Pleasant Municipal Airport (OSA) in Mount Pleasant, Texas. The flight, a positioning trip under 14 CFR Part 91, had departed Gilmer Municipal Airport (JXI) in Gilmer, Texas, with OSA as the intended destination. Visual meteorological conditions prevailed at the time of the incident. The aircraft was not damaged, and the commercial pilot was uninjured.
Pilot Actions
The pilot reported level flight at 2,000 feet mean sea level, approximately 10 miles from OSA, when the airplane initiated an un-commanded left roll. Upon disengaging the autopilot, the pilot discovered that the ailerons were unresponsive. Using rudder control only, the pilot successfully landed the aircraft at OSA.
Post-Incident Examination
A post-incident examination conducted by the operator revealed that the right wing (RW) primary aileron control cable was completely severed 13 inches from the threaded end, approximately at the location of an idler pulley. The idler pulley could not be rotated when manually manipulated. Additional wear spots—characterized by polishing or fraying—were observed on the RW primary cable, the RW balance cable, and the left wing (LW) primary and balance cables. A dark, grease-like material covered the failure area of the RW primary cable and was also found on the associated idler pulley. Another idler pulley for the RW balance cable was initially immobile but rotated freely after a firm twist produced a clicking sound.
FAA and Manufacturer Findings
Federal Aviation Administration inspectors examined the aircraft and components on August 5, 2010. They noted that the idler pulley at the cable failure location exhibited a manufacturing flaw: the pulley was not machined completely through, creating a lip that prevented the bushing from fully passing through the idler pulley.
The suspect RW primary cable idler pulley and sections of the broken cable were sent to the manufacturer for further analysis. The inside diameter of the idler pulley’s outer bearing measured 0.0065 inches less than the component’s service limit. The submitted cable portion was found to be made of galvanized steel.
Manufacturer Service Bulletin
On October 19, 2010, Piper Aircraft, Inc. issued Service Letter No. 1135, a maintenance alert emphasizing the critical nature of control cable and pulley inspections. The alert highlighted recurring inspection requirements and included instructions for inspecting control cables and pulleys.