Incident Overview
During the takeoff rotation of a DHC-8 aircraft, the captain noted an uncommanded left roll. No warning lights or horns activated before or during the event. The pilot applied right control wheel and right rudder inputs to counteract the roll. After stabilizing the aircraft, the captain executed a wide left pattern and returned to the departure airport, where the airplane landed without further incident.
Post-Incident Inspection
A postincident examination of the aircraft revealed that the left inboard roll spoiler was jammed and partially deployed. Further disassembly of the roll spoiler servoactuator showed that a plug (part number A50993-1), which had been fusion-welded into the base of the piston (part number A50992-1), had separated. The separated plug lodged between the piston base and shims, restricting piston movement.
Manufacturer History
Dowty Aerospace, the manufacturer of the servoactuator, recorded six previous failures of fusion welds in pistons used on DHC-8 roll spoiler servoactuators before this incident.