What happened
The crew of a CRJ was performing a visual approach at night. During the transition of the wing flaps from 3D degrees to 45 degrees, the right wing flight spoiler experienced an uncommanded extension. This movement caused the aircraft to roll to the right, an action that the pilots successfully countered. Following the incident, the airplane continued its approach, landed without further incident, and taxied to the gate.
The investigation
A post-flight inspection of the aircraft revealed that the right wing flight spoiler remained extended by approximately 10 degrees. A subsequent metallurgical examination was performed on the component, which identified that the outboard lug on the flight spoiler had failed due to fatigue. Investigators also located fretting in the area adjacent to the fatigue fracture. It was noted that fatigue cracks can initiate within fretted areas at stress levels lower than those required for non-fretted areas.