Incident Overview
While in cruise flight at flight level 410 with the autopilot engaged, the crew experienced an uncommanded yaw to the right. The flight continued to its intended destination, where a normal landing was made without incident.
Examination Findings
Post-flight examination of the airplane's rudder control system revealed that the shaft portion of the rudder quadrant was fractured. Metallurgical evaluation of the fractured surface determined that the separation of the shaft portion resulted from stress corrosion cracking. The cracking initiated from opposite sides of the shaft and progressed inward until approximately 60% of the shaft cross section had cracked.
Contributing Factors
The stress corrosion cracking was attributed to three factors: a poor choice of material, an improper radius, and excessive torque applied to the shaft nut.
Conclusion
The incident was resolved without further event, and the aircraft landed normally. The identified material and manufacturing issues were addressed to prevent recurrence.