UNCOMMANDED ROLL WHILE ON AUTOPLT.

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BOEING 747-2 FREIGHTER ORD-ANC OPERATING ON 'A' AUTOPLT WITH PERFORMANCE MGMNT SYS ENGAGED. AUTOPLT TWICE DISCONNECTED WITH NO PERFORMANCE MGMNT SYS FAULTS NOTED. OPERATING ON 'A' AUTOPLT AND PERFORMANCE MGMNT SYS AND AUTOTHROTTLES ENGAGED; WITH INS SELECTED. OPERATING MIDWAY BTWN 2 CORRECT WAYPOINTS (5-6); ACFT STARTED AN UNCOMMANDED L ROLL. ROLL WAS SMOOTH AND FAIRLY RAPID. PASSING 15 DEGS L BANK; ROLL WAS NOTED AND AUTOPLT DISCONNECTED AND ROLL STOPPED. 'B' AUTOPLT USED REMAINDER OF TRIP WITH NO FURTHER PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS A CHK AIRMAN ON THE B-747. HE IS A CRUSADER TO KEEP THE COCKPIT WHITE LIGHTING 'OFF' WHILE FLYING AT NIGHT. HE BELIEVES THAT HE AND HIS CREW WERE ABLE TO FIND THIS BANK ANGLE CHANGE VERY QUICKLY BECAUSE THEY HAD AN OUTSIDE HORIZON AND WERE NOT DISTRACTED BY WHITE LIGHTS. HE ADMITS THAT HE IS FIGHTING A LOSING BATTLE OVER THE LIGHT ISSUE. HE THINKS THAT HIS INCIDENT WAS VERY MINOR BUT COULD HAVE BECOME DISASTROUS HAD THE TURN CONTINUED OR THE BANK ANGLE INCREASED. HIS ACR FOUND THAT THEE WAS A PROB WITH AN AUTOPLT SERVO THAT HAS SINCE BEEN CHANGED. HIS ACR PUBLISHED A BULLETIN TO ALL B-747 PLTS IN HIS COMPANY REGARDING THIS INCIDENT.