On August 29, 2003, at approximately 1635, a Cessna 650, N651EJ, experienced a right wing aileron cable failure while in cruise flight at FL390 approximately 200 miles southeast of Rapid City, South Dakota. The airline transport (ATP) rated pilot in command, the ATP rated co-pilot, and seven passengers on board were not injured. The 14 CFR Part 91 business flight was operating on an instrument flight rules flight plan in visual meteorological conditions. The flight originated from Marion, Illinois, about 1500 with the intended destination of the Rapid City Regional Airport (RAP). The pilot in command reported that with the autopilot engaged, the airplane started a gentle roll to the right. The autopilot was disengaged and an approximate 40 degree control wheel deflection to the left was made to keep the wings level. Positive roll control was available; however, the right aileron did not seem to move with control wheel deflection. The right roll control spoiler did respond to control wheel inputs. All left control surfaces appeared to function normally. The pilots consulted all control malfunction checklists, and there were no changes noted. The pilots decided to continue to destination with minimum maneuvering, for a straight in approach at RAP on runway 32 (8,600 feet long) with the wind closely aligned with the runway. The pilot in command noted that the airplane responded well to roll control inputs at lower airspeeds. An uneventful, full-flap landing was made at RAP. Maintenance personnel discovered a completely broken right outboard aileron cable. The right aileron cable (Part Number 6260106-25) underwent a metallurgical examination at Engineering Systems Inc. (ESI), Aurora, Illinois. ESI reported that the examination of the right aileron showed that the fracture ends were covered in grease and required cleaning using an ultrasonic cleaner with acetone. The cleaned wire stands displayed sheared and cut ends due to pinching. ESI further stated, these fractures are all typical of a wire rope cable coming off its large diameter pulley and being pulled over a small radius and being pinched. This creates the wear and loads necessary to start fracturing the outer strands and working in toward the center. Only a few tensile cup cone fractures were found, indicating nearly all the wire strands had been sheared or cut prior to final tensile separation of the few remaining strands. According to maintenance records, the airplane completed a phase 1-5 Citation continuous inspection program on June 25, 2003. The aileron cables and pulley assemblies were inspected at this time.