Narrative:

Air carrier X was being vectored for a left downwind for runway 21L at dtw. He was level at 11000 ft. Air carrier Y was climbing to 10000 ft eastbound (120 degree heading) off of dtw (air carrier Y was not TCASII equipped). Air carrier X began a descent, established on a 300 degree heading, head on with air carrier Y climbing out of 9400 ft for 10000 ft. He advised me he had gotten an RA and was descending. He was then out of 10700 ft. I immediately told air carrier X to 'not descend, the other aircraft was climbing to 10000 ft.' it appeared then that air carrier X was passing behind air carrier Y at 10700 ft. Air carrier Y was at 10000 ft. He then began a climb to 11200 st. This was very upsetting first because I had not seen a descent RA into a climbing aircraft before. Only once when TCASII was very new. This could have been disastrous. Air carrier Y, not having TCASII, had no idea of this situation and was going to level at 10000 ft. Meanwhile air carrier X is descending into his protected airspace. This is a controled environment where climbing and descending aircraft are separated by 1000 ft. There should be some limits to the maneuvers executed in regard to the RA, when in a TCA, in close proximity to the airport. This was just a little too close for my comfort. I trust the system and rely on the pilots to do what I direct. I lose faith in the system when the pilots can make such drastic deviations from their assigned altitudes and tell us after the fact.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR X TCASII RA DSCNT HAD LTSS FROM ACR Y. NON ADHERENCE TO ATC CLRNC. EVASIVE ACTION TAKEN.

Narrative: ACR X WAS BEING VECTORED FOR A L DOWNWIND FOR RWY 21L AT DTW. HE WAS LEVEL AT 11000 FT. ACR Y WAS CLBING TO 10000 FT EBOUND (120 DEG HDG) OFF OF DTW (ACR Y WAS NOT TCASII EQUIPPED). ACR X BEGAN A DSCNT, ESTABLISHED ON A 300 DEG HDG, HEAD ON WITH ACR Y CLBING OUT OF 9400 FT FOR 10000 FT. HE ADVISED ME HE HAD GOTTEN AN RA AND WAS DSNDING. HE WAS THEN OUT OF 10700 FT. I IMMEDIATELY TOLD ACR X TO 'NOT DSND, THE OTHER ACFT WAS CLBING TO 10000 FT.' IT APPEARED THEN THAT ACR X WAS PASSING BEHIND ACR Y AT 10700 FT. ACR Y WAS AT 10000 FT. HE THEN BEGAN A CLB TO 11200 ST. THIS WAS VERY UPSETTING FIRST BECAUSE I HAD NOT SEEN A DSCNT RA INTO A CLBING ACFT BEFORE. ONLY ONCE WHEN TCASII WAS VERY NEW. THIS COULD HAVE BEEN DISASTROUS. ACR Y, NOT HAVING TCASII, HAD NO IDEA OF THIS SIT AND WAS GOING TO LEVEL AT 10000 FT. MEANWHILE ACR X IS DSNDING INTO HIS PROTECTED AIRSPACE. THIS IS A CTLED ENVIRONMENT WHERE CLBING AND DSNDING ACFT ARE SEPARATED BY 1000 FT. THERE SHOULD BE SOME LIMITS TO THE MANEUVERS EXECUTED IN REGARD TO THE RA, WHEN IN A TCA, IN CLOSE PROX TO THE ARPT. THIS WAS JUST A LITTLE TOO CLOSE FOR MY COMFORT. I TRUST THE SYS AND RELY ON THE PLTS TO DO WHAT I DIRECT. I LOSE FAITH IN THE SYS WHEN THE PLTS CAN MAKE SUCH DRASTIC DEVS FROM THEIR ASSIGNED ALTS AND TELL US AFTER THE FACT.

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.