What was found
AUTOPILOT B DISENGAGED APPROX 3 HOURS 25 MINUTES INTO THE FLIGHT AT CRUISE ALT. UPON REENGAGEMENT, AIRCRAFT MOMENTARILY ROLLS LEFT THEN AUTOPILOT DISENGAGES. AUTOPILOT A WORKS NORMALLY. GROUNDED - YES. FAULT HISTORY SHOWS A/P DISC TWICE ON LEG 4 AT FL350. MSG 22-11505, AIL ACT 2. ACCOMPLISHED DFCS LIB TEST 21 AIL CH B AND 10 FCC, ALL TEST PASS REF B737-9 IFIM 22-11-00-810-831. REMOVED AND REPLACED AUTOPILOT AILERON ACTUATOR B, REF B737-9 AMM 22-11-25-000/400-801. GROUND VERIFICATION PASS. ALL LLM TEST PASS REF AMM 22-11-25-820-801.