B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 240; Flight Crew Total 30500; Flight Crew Type 10686
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Unstabilized Approach
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control
Aircraft
On descent on STAR into ZZZ; we were told to slow down to accommodate traffic ahead. As I was decelerating the aircraft through 270 to 250 (assigned) knots; the aircraft started a substantial roll. AUTOPILOT AND AUTOTHROTTLE WERE ON. I disengaged the autopilot to hand fly; and fully stowed the speed brakes. Despite speed brakes stowed; the aircraft rolling moment was quite different. Rudder ratio light came on a few seconds later. Ran the checklist; simultaneously we further reviewed the situation. Rudder and roll moment had a peculiar (bungee) feel to it.  Configured early and landed uneventfully. Had CFR equipment inspect the aircraft on landing; condition and fluids issues of at all. None found visually by CFR CREWS. Jump seater was put to use and was great assistance.
[Report narrative contained no additional information.]
Boeing 757 flight crew reported an uncommanded roll during descent with the autopilot engaged. The Rudder Ratio light illuminated a few seconds later.