AN SF340 FLEW THROUGH THE LOC OF APCH AT DTW. THE ACFT RECEIVED A TCASII TA AND EXECUTED A MISSED APCH FOLLOWED BY A SECOND APCH.

Narrative

APCHING RWY 3R IN DTW (ON AN ILS APCH); THE AUTOPLT SLIGHTLY OVERSHOT THE INBOUND LOC COURSE. WE HAD BEEN CLRED FOR THE APCH AND WERE SWITCHED TO TWR. WE THEN NOTICED THAT THE AUTOPLT WAS OVERSHOOTING THE LOC. THE PF THEN DISCONNECTED THE AUTOPLT TO CORRECT. SIMULTANEOUSLY WE RECEIVED A TA ON OUR TCASII AND TWR COMMANDED AN IMMEDIATE R TURN TO 090 DEGS AND A DSCNT TO 2400 FT. I LOOKED AND SAW THE TFC WELL ABOVE AND BEHIND US. AS WE TURNED; THE LOC RECTRED AND I ASKED THE TWR IF HE WOULD LIKE US TO REINTERCEPT AND CONTINUE THE APCH. HE TOLD US NO; AND THAT WE COULD CONTINUE OUR TURN TO 120 DEGS AND HE WOULD TAKE US OUT FOR A 'CLEAN' APCH. WE DID THIS AND AN UNEVENTFUL APCH AND LNDG FOLLOWED. WE WERE ASKED TO CONTACT TRACON AFTER ARR AND FROM THEM LEARNED THAT SEPARATION WAS NEVER LOST. THE FACTORS CONTRIBUTING TO THIS WERE: IMC -- WE WOULD NOT HAVE ALLOWED THIS OVERSHOOT IF THE WX HAD BEEN SUCH THAT THE RWY ENVIRONMENT COULD BE SEEN. CONGESTED AIR TFC AREA -- THERE WAS A HIGH CONCENTRATION OF TFC AND OUR WORKLOAD WAS VERY HIGH ON THIS PORTION OF THE APCH. FROM A HUMAN FACTORS STANDPOINT; WE WERE OVER-RELYING ON THE AUTOPLT. IN THIS SIT; I PERSONALLY HAVE LEARNED TO TRUST THE AUTOPLT VERY MUCH AND IN THIS SIT MAY HAVE BECOME COMPLACENT ENOUGH ABOUT IT THAT I WAS THINKING ABOUT OTHER ASPECTS OF THE FLT MORE THAN THE ACTUAL FLT PATH. IN THE FUTURE I WILL MONITOR THE AUTOPLT MUCH MORE CAREFULLY. ESPECIALLY IN CRITICAL PHASES OF FLT.