AN ACR ACFT HAS AN UNCOMMANDED ROLL TO THE R AND THE FLC FINDS THAT THE AILERONS ARE VERY HVY WHEN THEY CORRECT. THE ACFT HAD SEVERAL PRIOR INCIDENTS OF THIS NATURE. B737-200.

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BEGINNING A 6 LEG DAY WE RECEIVED A B737-200. REVIEWING THE MAINT LOGBOOK WE NOTED SEVERAL ENTRIES INDICATING NUMEROUS INCIDENTS OF UNCOMMANDED ROLL INVOLVING THE SP77 AUTOPLT. FIRST LEG 'FO'S LEG' WAS UNEVENTFUL FROM LAX TO LAS. LEG #2 WAS UNEVENTFUL UNTIL PASSING FL200 ON THE MODESTO ARR INTO SFO. IN CRUISE DSCNT AT APPROX 290 KIAS WE FELT WHAT APPEARED TO BE AN ABRUPT YAW (KICK) ALTHOUGH IT WAS WITNESSED BY BOTH CREW MEMBERS AND 2 JUMPSEATERS (FROM OTHER AIRLINES -- BOTH CAPTS). WE COULD NOT CONFIRM THE DIRECTION IT YAWED. WITHIN 4 MINS WHILE PASSING 12000 FT MSL; THE CAPT'S HDG BUG WAS ADJUSTED 5 DEGS L. AT THIS POINT ALL 4 PLTS ON THE FLT DECK WITNESSED THE ACFT ROLL SLOWLY TO THE R. BEFORE REACHING 30 DEGS BANK THE AUTOPLT WAS DISCONNECTED BY THE CAPT. FINDING THE CTLS VERY HVY ABOUT THE ROLL AXIS; CTL WAS RELINQUISHED TO THE FO; WHO ALSO FOUND THE CTLS DIFFICULT ABOUT THE ROLL AXIS. WITHIN 10 SECONDS; NORMAL CTL WAS RESTORED AND THE CAPT FLEW THE ACFT MANUALLY TO THE DEST WITH NO FURTHER INCIDENT. AFTER LNDG; CONTRACT MAINT INSPECTED THE ACFT AND THEN THE CREW FERRIED IT TO OUR MAINT BASE WITHOUT USING AUTOPLT OR YAW DAMPER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT OF THIS B737-200 SAID THAT THE PREVIOUS WRITE-UPS INDICATED THAT THE ACFT WOULD ROLL; USUALLY TO THE R; AND THAT THE AUTOPLT WAS SUSPECTED TO BE AT FAULT. THE RPTR SAID THAT WHEN THE ACFT ROLLED TO THE R ON HIM; AND HE DISCONNECTED THE AUTOPLT; THE AILERONS FELT VERY HVY WHEN HE ATTEMPTED TO ROLL TO THE L TO CORRECT. HE DESCRIBED THE FEEL TO BE AS THOUGH THE PWR STEERING ON A CAR HAD FAILED. THE FO CONFIRMED THE CTL STIFFNESS. THE RPTR SAID THAT SUDDENLY THE CTLS RETURNED TO NORMAL AND THIS PHENOMENON DID NOT RECUR. THE MAINT PERSONNEL THOUGHT THAT THE AUTOPLT WAS THE SOURCE OF THE PROB; BUT THE RPTR DOES NOT KNOW THE RESULT OF THEIR INVESTIGATION. HE SAID THAT HE THOUGHT THAT THE AUTOPLT WAS ALSO THE CAUSE FROM THE FIRST MOMENT THAT HE READ THE WRITE-UPS.