Occurrence
While on final approach, the airplane commenced a rapid, uncommanded roll to the right when the 35-degree flap setting was selected. The flying pilot, the 1st officer, was able to counter the roll by applying almost full opposite aileron. During this application, he felt the aileron jam momentarily and then break free. The airplane landed without further incident.
Examination Findings
A post-incident examination revealed that the inboard, aft end of the right wing outboard flap was detached from the wing flap track. This detachment resulted in flap asymmetry and mechanical interference with the aileron. The flap track roller bearing was seized, and the flap mounting bracket was torn and separated from the bearing. The bearing outer roller was loose and could be shifted axially on the bearing outer ring. This allowed the outer roller flange to wear against and eventually tear through the flap mounting bracket.
Maintenance Issues
The operator was not using the most recent (revised) Beech 1900D maintenance manuals at the time of the incident. Consequently, the airplane had not been subjected to a detailed inspection of the flap roller brackets, roller bearings, and attachment hardware as outlined in revised sections of the manual.