What happened
While operating in cruise flight at FL410 with the autopilot engaged, the crew experienced an uncommanded yaw to the right. Following the event, the aircraft completed a normal landing at its intended destination without incident. There were no injuries reported.
The investigation
An examination of the aircraft's rudder control system revealed that the shaft portion of the rudder quadrant had fractured. A metallurgical evaluation of the fracture surface was performed to determine the nature of the failure. This analysis showed that the separation of the shaft portion was caused by stress corrosion cracking. The cracks initiated from opposite sides of the shaft and progressed inward until approximately 60% of the shaft cross section had cracked.
Findings
The investigation identified three primary factors that contributed to the development of the stress corrosion cracking: a poor choice of material, an improper radius, and the application of excessive torque on the shaft nut.