What happened
During the final approach phase of flight, the Beech 1900D experienced a rapid, uncommanded roll to the right immediately after the pilot selected the 35-degree flap setting. The first officer, acting as the flying pilot, attempted to counteract the roll by applying nearly full opposite aileron. During this maneuver, the pilot felt the aileron jam momentarily before breaking free. Despite the disturbance, the aircraft landed without further incident.
The investigation
Mechanical examination of the aircraft revealed that the inboard, aft end of the right wing outboard flap had detached from the wing flap track. This detachment created flap asymmetry and caused mechanical interference with the aileron control surface. Investigators found that the flap track roller bearing had seized, which led to the flap mounting bracket tearing and separating from the bearing. Additionally, the bearing outer roller was loose enough to shift axially on the bearing outer ring; this movement allowed the outer roller flange to wear against and eventually puncture the flap mounting bracket.