ACR X TCASII RA DSCNT CAUSED LTSS FROM ACR Y. PLTDEV.

Narrative

I WAS WORKING THE E FEEDER POS WORKING ARRS TO DTW RWY 3R. ACR X COMING FROM THE NE AT 12000 FT WAS BEING VECTORED TO A POINT NE OF DTW TO TURN DOWNWIND. ACR X DEPARTED DTW CLBING TO 10000 FT WAS TURNED TO A 120 DEG HDG TO JOIN THE SID. I DSNDED ACR X HVY TO 11000 FT THEN TO SLOW 70 210 KTS. I ALSO CALLED TFC TO ACR X HVY AS 2 O'CLOCK; 7 MI SEBOUND AT 10000 FT. ACR X HVY LEVELED AT 11000 FT AND ASKED HIS SEQUENCE. I ADVISED HE WAS #6 AND TURNED HIM TO A 210 DEG HDG. 30 SECONDS LATER ACR X ADVISED HE WAS GETTING AN RA ON TCASII AND HE WAS DSNDING! AT THIS TIME THE TFC; ACR Y; WAS 12 O'CLOCK AND 1 1/2 - 2 MI AWAY! I KEYED THE MIKE; ROGERED THE XMISSION AND ADVISED THE TFC WAS AT 10000 FT. ACR X HVY ROGERED THE XMISSION AND 45 SECONDS LATER RPTED BACK AT 11000 FT. THE CLOSEST THE ACFT CAME WAS 500 FT VERT AND ABOUT 1 MI LATERAL. STANDARD IFR SEPARATION AND HVY JET SEPARATION WAS NOT MAINTAINED BECAUSE OF THE TCASII RESOLUTION. I HAVE ALSO SEEN AND HEARD OF OTHER SITS WHEN TCASII HAS CAUSED LTSS; BUT IN THOSE INSTANCES; THE HIGHER ACFT WAS DSNDING TO AN ALT 1000 FT ABOVE THE ALT THE LOWER ACFT WAS CLBING TO. IN THIS INSTANCE; BOTH ACFT WERE IN LEVEL FLT WHEN THE TCASII RESOLUTION OCCURRED. ADDITIONALLY; ACR X WENT DOWN TO 10500 FT AS A RESULT OF ACR Y; BUT THERE WAS A THIRD ACFT THAT WAS CLBING TO 10000 FT (LEAVING 7800 FT) THAT WAS 4 MI FROM ACR X AND CLOSING. THERE WAS NO LOSS OF SEPARATION BTWN ACFT #3 AND ACR X. TCASII WORKS WELL -- IN THEORY! I WOULD CLASSIFY THIS AS A NMAC IN THE NATIONAL AIRSPACE SYS CAUSED BY TCASII. BOTH ACFT WERE SEPARATED BY THE SAFETY REQUIREMENTS OF THE FAA'S 7110.65G HANDBOOK; BUT DETERIORATED DUE TO AN ELECTROMECHANICAL BLACK BOX WHICH DID NOT TAKE ALL FACTORS INTO ACCOUNT; I.E.; BOTH ACFT LEVEL; ACFT #3 CLBING; THE TURN OF ACR X HVY TO DOWNWIND; ETC.