B737-500 RPTS POSSIBLE UNCOMMANDED RUDDER DEPLOYMENT JUST PASSING OUTER MARKER AT DIA.

Narrative

FO FLYING. UNCOMMANDED RUDDER DEFLECTION. VISUAL APCH TO RWY 35L AT DEN. 3-4 MI BEHIND A B737 WE ENCOUNTERED WHAT SEEMED TO BE HVY WAKE TURB. THEN SMOOTH AIR FOR A FEW SECONDS THE ACFT BEGAN TO ROLL R. THE FO CORRECTED WITH L AILERON. ACFT BEGAN TO RESPOND THEN ROLLED FURTHER R APPROX 30 DEGS AND NOSE DOWN. THE FO APPEARED TO HAVE FULL L AILERON AND ACFT WAS NOT RESPONDING FOR 2-3 SECONDS. I CALLED FOR A GAR. ACFT RESPONDED. WE LANDED UNEVENTFULLY ON RWY 35R. FO STATED THAT DURING THE SECOND ROLL TO THE R; THE RUDDER DEFLECTED 1/4 - 1/2 OF ITS FULL TRAVEL UNCOMMANDED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATES THAT AS PNF; HE FIRST ASSUMED THAT THIS INCIDENT WAS DUE TO WAKE TURB; BUT THE FACT THAT THE TFC BEING FOLLOWED WAS ANOTHER B737 ALONG WITH THE FO REACTIONS OF FULL THROW ON THE AILERONS CAUSED HIM TO DECIDE TO RPT AS A POSSIBLE RUDDER PROB. AS A RESULT; THE FLT RECORDER TAPES WERE REMOVED. BOEING PERSONNEL; ACR PERSONNEL; PLT GROUP AND MAINT PERSONNEL WERE INVOLVED. ALL PARTIES; INCLUDING THE RPTR; NOW AGREE THAT THE CAUSE WAS ONE OF WAKE TURB FROM THE RPTED TFC; A B737; 3-4 MI AHEAD OF THE RPTR ACFT.