Dash 8-400
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface
Aircraft Equipment Problem Critical
Aircraft Equipment Problem Dissipated
Aircraft
On departure the aircraft required excessive RWD [Right Wing Down] roll trim in cruise and the control yoke was turned to the right about 20 degrees. We did not observe any indication of spoilers deployed on the PFCS [Primary Flight Control System] display panel or a spoiler push off button illuminated on the glare shield.After approximately 20 minutes in flight the aircraft rolled to the left abruptly and needed to be re-trimmed. Aileron trim was closer to normal position when trimmed and the roll control was normal. After further research it was determined from the flight [data] recorder system that one of the in- board roll spoilers did not stow on takeoff and was deployed approximately 20 degrees. I was the pilot flying during this takeoff and normally the flying pilot does not check the indication of the roll spoilers on power up. Better training of how the roll spoiler system works and how to determine if a spoiler is deployed would be beneficial to improved flight crew understanding.
When their Dash 8 required excessive right wing down roll trim after takeoff the flight crew trimmed as necessary and continued their flight. Later the aircraft rolled abruptly left and the trim returned to a more normal centered condition. Post flight FDR investigation revealed that one inboard roll spoiler had failed to stow on takeoff and; subsequently did stow itself resulting in the two trim anomalies.