Originally Posted by HN39
Perhaps it is slightly more complicated. The drag due to downward deflection of the aileron on one wing is largely compensated by the drag of the spoilers extending on the other wing, and the yaw damper is still active.
And it is still probably more complicated than that with rapid reversing control inputs. If the response time of ailerons and spoilers are not perfectly matched while transitioning, you might be off the planned schedule and creating additional yaw.
Normally, with a brief interval of mismatch, this is no big deal. However, when the controls are continually transitioning as in the case of a roll PIO, the percentage of time that this potential imbalance applies is greater and may be the source of yaw inputs to the airframe.
Having flown jet aircraft with aileron only roll control, spoiler only roll control, and combination aileron spoiler-aileron roll control, I prefer the combination approach, but spoilers can create cruise inefficiency with a heavy wing. For that reason, spoilers often only move with larger roll inputs, and smaller inputs are handled with the ailerons only. I do not know how the A330 gears the relationship between ailerons and spoilers.