Incident Summary
A CRJ aircraft, operating during a night visual approach, experienced an uncommanded extension of the right wing flight spoiler as the wing flaps were extended from 30 degrees to 45 degrees. The extension induced a roll to the right, which the flight crew promptly countered. The crew continued the approach, and the aircraft landed without further incident, subsequently taxiing to the gate.
Post-Flight Findings
A post-flight inspection of the right wing revealed the flight spoiler was extended approximately 10 degrees. Metallurgical examination of the spoiler assembly identified that the outboard lug on the flight spoiler had failed due to fatigue. Additionally, fretting damage was observed adjacent to the fatigue fracture.
Metallurgical Analysis
According to the METALS HANDBOOK, fatigue cracks can initiate in fretted areas at stress levels below those required for non-fretted zones. This finding is consistent with the observed failure mode of the outboard lug.