Narrative:

I was working the east feeder position working arrs to dtw runway 3R. Air carrier X coming from the northeast at 12000 ft was being vectored to a point northeast of dtw to turn downwind. Air carrier X departed dtw climbing to 10000 ft was turned to a 120 degree heading to join the SID. I descended air carrier X heavy to 11000 ft then to slow 70 210 KTS. I also called traffic to air carrier X heavy as 2 O'clock, 7 mi sebound at 10000 ft. Air carrier X heavy leveled at 11000 ft and asked his sequence. I advised he was #6 and turned him to a 210 degree heading. 30 seconds later air carrier X advised he was getting an RA on TCASII and he was descending! At this time the traffic, air carrier Y, was 12 O'clock and 1 1/2 - 2 mi away! I keyed the microphone, rogered the transmission and advised the traffic was at 10000 ft. Air carrier X heavy rogered the transmission and 45 seconds later reported back at 11000 ft. The closest the aircraft came was 500 ft vertical and about 1 mi lateral. Standard IFR separation and heavy jet separation was not maintained because of the TCASII resolution. I have also seen and heard of other sits when TCASII has caused less than standard separation, but in those instances, the higher aircraft was descending to an altitude 1000 ft above the altitude the lower aircraft was climbing to. In this instance, both aircraft were in level flight when the TCASII resolution occurred. Additionally, air carrier X went down to 10500 ft as a result of air carrier Y, but there was a third aircraft that was climbing to 10000 ft (leaving 7800 ft) that was 4 mi from air carrier X and closing. There was no loss of separation between aircraft #3 and air carrier X. TCASII works well -- in theory! I would classify this as a near midair collision in the national airspace system caused by TCASII. Both aircraft 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 aircraft level, aircraft #3 climbing, the turn of air carrier X heavy to downwind, etc.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.