What happened
During the takeoff rotation phase, the DHC-8 experienced a sudden roll to the left. The captain reported that no warning lights or horns were activated before or during the event. To counteract the left roll, the pilot applied right rudder and right control wheel input. Once the aircraft's roll was stabilized, the crew executed a wide left pattern and returned to the departure airport, where the airplane was landed without further incident. No injuries were reported.
The investigation
A post-incident inspection of the aircraft identified that the left inboard roll spoiler was partially deployed and jammed. Upon the disassembly and examination of the roll spoiler servoactuator, investigators found that a plug (PN A50993-1) had separated from its position. This plug had been fusion-welded into the base of the piston (PN A50992-1). Following the separation, the plug became lodged between the shims and the base of the piston, which restricted the movement of the piston.