A HDG TRACK DEV PRODUCES A POTENTIAL CONFLICT WITH OTHER ARR TFC.

Narrative

PARALLEL APCHS WERE BEING CONDUCTED AT MSP ON RWYS 29L/29R. WE HAD BEEN CLRED FOR VISUAL APCH ON RWY 29R. (FIELD IN SIGHT). I ENGAGED THE AUTOPLT TO CONDUCT AN AUTOMATED TURN ON TO THE LOC AND GS. (I INTENDED TO DISENGAGE THE AUTOPLT ONCE CAPTURE AND TRACKING OCCURRED). (WE DO THIS RANDOMLY TO CHK AUTOPLT CAT II CERTIFICATION). ALL SIGNALS WERE NORMAL AND SWITCHES ON THE AUTOPLT CORRECT. THE AUTOPLT WAS IN THE HDG MODE AND ARMED FOR CAPTURE. HDG WAS 260 DEGS (40 DEGS INTERCEPT). APCHING THE LOC THE AUTOPLT STARTED A SLOW TURN TOWARD THE RWY (WE WERE ABOUT 12 MI FROM RWY). IT ONLY BANKED THE ACFT ABOUT 5-10 DEGS (VERSUS THE NORMAL 20-25 DEGS). WE WENT THROUGH THE LOC. I SWITCHED THE AUTOPLT OFF AND INCREASED BANK ANGLE MANUALLY TO 30 DEGS TO RE-INTERCEPT LOC. ABOUT THIS TIME THE TCASII PRODUCED AN 'RA' AND A 'DO NOT DSND.' I MAINTAINED ALT. UPON VISUALLY CHKING I NOTICED A TURBOPROP COMMUTER PLANE ON OUR L SIDE ON A STRAIGHT IN APCH TO RWY 29L. HE WAS APPROX 300 FT BELOW US AND PERHAPS LESS THAN 1000 FT HORIZ DISTANCE. I MANEUVERED OUR ACFT BACK TO THE LOC AND MAINTAINED ALT UNTIL ON LOC. 'CLR OF CONFLICT' SOUNDED WHILE DOING THIS. UPON INTERCEPTING THE LOC I DSNDED TO INTERCEPT THE GS. THE REMAINDER OF APCH WAS NORMAL. THE FREQS (COM) WERE DIFFERENT FOR RWYS 29L AND 29R. THE TFC HAD NOT BEEN POINTED OUT UNTIL AFTER WE HAD ESTABLISHED VISUAL CONTACT AND THE TCASII SOUNDED 'RA.' OUR EXCURSION DID NOT TAKE US PAST THE MIDPOINT BTWN THE 2 PARALLEL RWYS. HOWEVER; I SHOULD HAVE REACTED A LITTLE SOONER WHEN THE AUTOPLT MALFUNCTIONED AND THUS WOULD HAVE AVOIDED THE SIZEABLE OVERSHOOT THAT OCCURRED.