Narrative:

Air carrier X was issued altitude of 11000 (climbing) and air carrier Y was descending to 8000. I was anticipating air carrier X to climb above air carrier Y. It appeared that air carrier X stopped the climb at 9000 and that the air carrier Y had stopped his descent at 10000. Traffic was issued and then both aircraft advised that they had TCASII RA. Only air carrier X had any TCASII information on the flight strip. I was taking into consideration both aircraft performances at the time, and thought that it was not going to be a problem. The sector I was working was busy and we were trying to open another radar sector to alleviate some of the traffic. Being busy, I was unable to watch the situation as it developed. Being a little more cautious in assigning altitudes will be one of the considerations. But also, when TCASII is involved, I've noticed that sometimes the pilot decides whether it is safe or not to climb/descend and that changes the controller's plans. Sometimes unintentionally. Supplemental information from acn 226989: air carrier X during climb from ont on the prado 2 departure we were cleared to 11000 ft. As we passed 9000 MSL, we received a TCASII TA followed immediately by an RA commanding a descent of at least 2000 FPM. At about the same time, the departure controller asked air carrier Y if he was climbing. The crew said they were responding to an RA and had stopped their descent and were leveling at 10000. I was flying and saw air carrier Y and descended from approximately 9300 ft to 9000 ft. The first officer confirmed we had been cleared to 11000 and we advised the controller in response to an RA we had stopped our climb and were level at 9000. Air carrier Y also confirmed that he had been cleared to 8000. When the aircraft were clear, we each continued to our assigned altitudes. The controller seemed completely unconcerned. We believe we came within 700 ft at 2.5 NM and would have been on a potential collision course if both crews had not responded to their TCASII. We were on a southeasterly course and air carrier Y was approximately west course. This put him behind my left window post and prevented an earlier visual sighting.

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Original NASA ASRS Text

Title: ACR X AND ACR Y TCASII TA RA NON ADHERENCE TO ATC CLRNC STOPPED CLB AND DSCNT HAD LTSS. EVASIVE ACTION TAKEN.

Narrative: ACR X WAS ISSUED ALT OF 11000 (CLBING) AND ACR Y WAS DSNDING TO 8000. I WAS ANTICIPATING ACR X TO CLB ABOVE ACR Y. IT APPEARED THAT ACR X STOPPED THE CLB AT 9000 AND THAT THE ACR Y HAD STOPPED HIS DSCNT AT 10000. TFC WAS ISSUED AND THEN BOTH ACFT ADVISED THAT THEY HAD TCASII RA. ONLY ACR X HAD ANY TCASII INFO ON THE FLT STRIP. I WAS TAKING INTO CONSIDERATION BOTH ACFT PERFORMANCES AT THE TIME, AND THOUGHT THAT IT WAS NOT GOING TO BE A PROB. THE SECTOR I WAS WORKING WAS BUSY AND WE WERE TRYING TO OPEN ANOTHER RADAR SECTOR TO ALLEVIATE SOME OF THE TFC. BEING BUSY, I WAS UNABLE TO WATCH THE SIT AS IT DEVELOPED. BEING A LITTLE MORE CAUTIOUS IN ASSIGNING ALTS WILL BE ONE OF THE CONSIDERATIONS. BUT ALSO, WHEN TCASII IS INVOLVED, I'VE NOTICED THAT SOMETIMES THE PLT DECIDES WHETHER IT IS SAFE OR NOT TO CLB/DSND AND THAT CHANGES THE CTLR'S PLANS. SOMETIMES UNINTENTIONALLY. SUPPLEMENTAL INFO FROM ACN 226989: ACR X DURING CLB FROM ONT ON THE PRADO 2 DEP WE WERE CLRED TO 11000 FT. AS WE PASSED 9000 MSL, WE RECEIVED A TCASII TA FOLLOWED IMMEDIATELY BY AN RA COMMANDING A DSCNT OF AT LEAST 2000 FPM. AT ABOUT THE SAME TIME, THE DEP CTLR ASKED ACR Y IF HE WAS CLBING. THE CREW SAID THEY WERE RESPONDING TO AN RA AND HAD STOPPED THEIR DSCNT AND WERE LEVELING AT 10000. I WAS FLYING AND SAW ACR Y AND DSNDED FROM APPROX 9300 FT TO 9000 FT. THE FO CONFIRMED WE HAD BEEN CLRED TO 11000 AND WE ADVISED THE CTLR IN RESPONSE TO AN RA WE HAD STOPPED OUR CLB AND WERE LEVEL AT 9000. ACR Y ALSO CONFIRMED THAT HE HAD BEEN CLRED TO 8000. WHEN THE ACFT WERE CLR, WE EACH CONTINUED TO OUR ASSIGNED ALTS. THE CTLR SEEMED COMPLETELY UNCONCERNED. WE BELIEVE WE CAME WITHIN 700 FT AT 2.5 NM AND WOULD HAVE BEEN ON A POTENTIAL COLLISION COURSE IF BOTH CREWS HAD NOT RESPONDED TO THEIR TCASII. WE WERE ON A SOUTHEASTERLY COURSE AND ACR Y WAS APPROX W COURSE. THIS PUT HIM BEHIND MY L WINDOW POST AND PREVENTED AN EARLIER VISUAL SIGHTING.

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.