A B737-300 ON LNDG ROLL EXPERIENCED FULL R AILERON BOUND AT THE STOPS CAUSED BY FAILED RIVETS IN FO'S LOWER CTL COLUMN.

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FO FLYING VISUAL APCH TO RWY 25L; RPTED WINDS 320 DEGS AT 20 KTS. ON ROLLOUT; I NOTICED HE HELD HIS R AILERON DOWN AND MOMENTARILY SEEMED TO RELEASE A BIT OF PRESSURE; BUT AGAIN SEEMED TO ADD ADDITIONAL R AILERON ALL THE WAY TO THE STOP. AT THIS POINT; I NOTED THAT WE WERE GOING TO PASS THE FIRST HIGHSPD TURNOFF. I COMMENTED '100 KTS; USE A LITTLE MORE REVERSE.' I WAS AWARE OF HIS FULL AILERON DEFLECTION WITH WHAT SEEMED TO BE NO DRIFT AT ALL. I SAID I HAD THE ACFT AND TOOK CTL. WHEN I WENT TO REDUCE AILERON PRESSURE; I FOUND IT STUCK TO THE STOPS; R DEFLECTION. WE TAXIED OFF ACTIVE IN THAT CONFIGN. I THEN ASKED HIM WHEN IT HAD BOUND. HE FELT THAT ON THE LNDG ROLLOUT I HAD 'ASSISTED' HIM WITH ADDITIONAL R AILERON. HE WASN'T SURE WHY. SO WE BOTH THOUGHT THE OTHER WAS ADDING R PRESSURE. I TAXIED TO GATE; CALLED MAINT AND NOTED R AILERON TRIM AT; I BELIEVE; 12% (ALL THE WAY TO THE R); PITCH 5% NOSE UP; AND NO RUDDER TRIM INPUT. WE LEFT ACFT WITH MAINT FOR FURTHER INVESTIGATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FAA AND BOEING ARE INVESTIGATING THIS INCIDENT AS IT HAS HAPPENED BEFORE ON B737 EQUIP. THE RPTR SAID THE CAUSE OF THE AILERONS BEING BOUND UP IN FULL R AILERON DEFLECTION WAS THE FAILURE OF RIVETS ON THE FO'S LOWER CTL COLUMN INTERFERING WITH THE BUS DRUM AND LOST MOTION DEVICE ASSEMBLY. THE RPTR STATED THE LOWER COLUMN HAD BEEN MODIFIED PREVIOUSLY BUT ON THIS ACFT AN UNMODIFIED PART WAS DISCOVERED. THE RPTR SAID NO FINAL RPT HAS BEEN RECEIVED BY THE RPTR FROM MAINT; FAA OR THE MANUFACTURER.