ACR X HAS LTSS FROM ACFT Y. SYS ERROR. TCASII TA EVASIVE ACTION TAKEN. ACFT EQUIP PROBLEM TCASII RA INOPERATIVE.

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PER COMPANY BULLETIN (DUE TO PROBLEMS WITH RA MODE); WE WERE OPERATING TCASII IN TA MODE; TFC SW AUTO. TSTMS S AND E OF DTW REQUIRED CHANGE OF PLANS FROM ILS 3R TO 3L. WE WERE ACR X LEVEL AT 11000 HAVING JUST PASSED OVER DTW WNW BOUND. TCASII CALLED 'TFC' AND WE OBSERVED TARGET AT 1-2 O'CLOCK; CONVERGING; 400 FT ABOVE US DSNDING. NO RESOLUTION ADVISORY (TURNED OFF) OR VISUAL CONTACT. RESISTING URGE TO BEGIN DSCNT I ASKED ATC 'WHAT ABOUT 12 O'CLOCK TFC FOR US?' ATC RESPONDED WITH CLRNC TO DSND TO 7000. WHILE FO MADE AGGRESSIVE DSCNT (SPDBRAKES; HARDOVER)(TCASII SHOWED TFC INSIDE 2 MI RING CONVERGING AT PLUS 200 FT DSNDING) ATC CLRED THE OTHER ACFT Y TO CLB TO 12000 IMMEDIATELY AND TURN L. WE DID SEE TFC AT 1 O'CLOCK HIGH BUT COULD NOT JUDGE PROX. AFTER CLRING; ATC ASKED US TO EXPEDITE DSCNT. AFTER CONFLICT WAS RESOLVED; ATC THANKED US FOR OUR HELP AND I REPLIED 'TCASII SURE CAME IN HANDY TONIGHT.' I FEEL THE TFC LEVEL AND WX MAY HAVE PUT THE CTLR JUST BEYOND HIS CAPABILITY. HE SOUNDED LIKE HE WAS WORKING VERY HARD BUT VERY COMPETENT. BY HIS REACTION THOUGH I THINK OUR SITUATION CAUGHT HIM BY SURPRISE. LACK OF TCASII RESOLUTION ADVISORY CAUSED US MUCH INITIAL CONFUSION (FOR A COUPLE SECONDS) ABOUT WHAT TO DO. FORTUNATELY; THE FREQ WAS AVAILABLE FOR A TIMELY QUERY AND CLRNC OR EMER AUTHORITY WOULD HAVE BEEN USED TO TAKE EVASIVE ACTION (DEVIATE FROM ASSIGNED ALT) BASED SOLELY ON A BLIP AND DATA BLOCK ON THE IVSI. SUPPLEMENTAL INFO FROM ACN 187470. WE HAD BEEN ON VECTORS FROM DTW APCH CTL. FLT WAS LEVEL AT 11000 FT AND ON A NW HDG. TCASII WAS INSTALLED ON THE ACFT AND FUNCTIONING IN THE 'TA' MODE DUE TO A 'FLT INFO FILE DISTRIBUTED TO CREW MEMBERS. IT READS AS FOLLOWS: 'IT HAS BEEN DISCOVERED THAT CERTAIN TRANSPONDERS INSTALLED ON THESE AIRPLANE TYPES MAY RANDOMLY PROVIDE INCORRECT ALT RESOLUTION DATA TO THE TCASII COMPUTER. UNTIL FURTHER NOTICE; TCASII SHOULD BE OPERATED IN THE TA MODE ON THESE AIRPLANE TYPES.' THE CREW RECEIVED A TFC ADVISORY FROM TCASII (BOTH VOICE AND PICTORIALLY) THAT TFC WAS ABOUT 1 O'CLOCK AND AT THE 2 MI RING; PLUS 400 FT AND DSNDING. I WANTED TO IMMEDIATELY DSND TO AVOID CONFLICT. THE CAPT SAID TO HOLD OFF; AND LUCKILY WAS ABLE TO GET THROUGH TO DTW APCH TO ASK 'WHAT ABOUT THE TFC AT 12 O'CLOCK.' THE CTLR GAVE US A DSCNT TO 7000 FT AND A TURN TO ABOUT 250 DEG HDG; FOLLOWED BY 'EXPEDITE DSCNT'. I IMMEDIATELY WENT TO FLT IDLE; SPDBRAKES DEPLOYED; AND INITIATED A DSNDING TURN. TARGET THEN SHOWED ON TCASII SCREEN 'PLUS 100 DSNDING' AND I LOOKED OUT THE WINDOW AND SAW A SET OF NAV LIGHTS GO OVER US. THE CAPT LATER INFORMED ME THAT THE ACFT HAD BEEN GIVEN AN EXPEDITE CLB INSTRUCTION FROM THE CTLR; SO IT APPEARED TO BE GREATER THAN 100 FT WHEN I SAW THE LIGHTS. WE WERE GIVEN A HDOF; THE CAPT SAID 'TCASII COME IN REAL HANDY' AND THE CTLR SAID THANKS A LOT FOR THE HELP. WERE THEN HANDED OFF TO APCH ON 124.07; I BELIEVE. I THINK A LARGE CONTRIBUTING FACTOR TO THIS WAS THAT THE WX WAS VERY BAD IN THE S AREA OF DETROIT. NUMEROUS TSTMS ALONG THE APCH PATHS MAY HAVE CAUSED A BUNCHING OF TFC. THE ONE THING I THINK I WOULD DO DIFFERENTLY GIVEN THE SAME SITUATION; IS TO OPERATE THE TCASII IN 'ON' RATHER THAN IN 'AUTO' MODE. WE MAY HAVE DETECTED THE CONFLICT SOONER AS PROXIMATE TFC RATHER THAN AS CONFLICT TFC.