Narrative:

Air carrier X was at FL260. I climbed government Y to FL250. I was working paxto hi sector, ZFW, at an extremely busy time. Air carrier X called to say he was taking a TCASII resolution and descending. I looked at Y's full data block and saw the reported altitude of FL254. I immediately stated to Y that his assigned altitude was FL250. Y said, 'roger, I am leveling at FL250.' I told air carrier X to return to FL260, that the Y was at FL250. Obviously, these aircraft were converging. Had air carrier X not had TCASII, the incident still may have happened. The unknown in this case is whether the Y would have stopped at FL250 had I not said anything. My feeling is that the Y probably saw the air carrier, realized he had overshot his altitude and got back to FL250 in the quickest way possible. With our computer we only get updates every 10 seconds, so when I saw FL254 on the Y, he had probably already started back to FL250. Because aircraft can arbitrarily leave their assigned altitudes in positive control area, I don't like TCASII used in ctrs. It was very disturbing, disorienting, and disruptive to my ATC performance to have this happen. I recommend no TCASII in positive control area. Supplemental information from acn 232160: air carrier X at FL260, proceeding direct to scy VOR, TCASII TA received. Aircraft approaching and climbing from 1:30 position. TCASII RA commanded descent and government Y aircraft spotted visually. Started descent and advised ZFW. At FL257 government Y observed descending as TCASII commanded a climb. Kept government Y visual and climbed back to FL260.

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Original NASA ASRS Text

Title: GOV Y CLB THROUGH ASSIGNED ALT HAD LTSS FROM ACR X TCASII TA RA EVASIVE ACTION TAKEN DSND. PLTDEV.

Narrative: ACR X WAS AT FL260. I CLBED GOV Y TO FL250. I WAS WORKING PAXTO HI SECTOR, ZFW, AT AN EXTREMELY BUSY TIME. ACR X CALLED TO SAY HE WAS TAKING A TCASII RESOLUTION AND DSNDING. I LOOKED AT Y'S FULL DATA BLOCK AND SAW THE RPTED ALT OF FL254. I IMMEDIATELY STATED TO Y THAT HIS ASSIGNED ALT WAS FL250. Y SAID, 'ROGER, I AM LEVELING AT FL250.' I TOLD ACR X TO RETURN TO FL260, THAT THE Y WAS AT FL250. OBVIOUSLY, THESE ACFT WERE CONVERGING. HAD ACR X NOT HAD TCASII, THE INCIDENT STILL MAY HAVE HAPPENED. THE UNKNOWN IN THIS CASE IS WHETHER THE Y WOULD HAVE STOPPED AT FL250 HAD I NOT SAID ANYTHING. MY FEELING IS THAT THE Y PROBABLY SAW THE ACR, REALIZED HE HAD OVERSHOT HIS ALT AND GOT BACK TO FL250 IN THE QUICKEST WAY POSSIBLE. WITH OUR COMPUTER WE ONLY GET UPDATES EVERY 10 SECONDS, SO WHEN I SAW FL254 ON THE Y, HE HAD PROBABLY ALREADY STARTED BACK TO FL250. BECAUSE ACFT CAN ARBITRARILY LEAVE THEIR ASSIGNED ALTS IN PCA, I DON'T LIKE TCASII USED IN CTRS. IT WAS VERY DISTURBING, DISORIENTING, AND DISRUPTIVE TO MY ATC PERFORMANCE TO HAVE THIS HAPPEN. I RECOMMEND NO TCASII IN PCA. SUPPLEMENTAL INFO FROM ACN 232160: ACR X AT FL260, PROCEEDING DIRECT TO SCY VOR, TCASII TA RECEIVED. ACFT APCHING AND CLBING FROM 1:30 POS. TCASII RA COMMANDED DSCNT AND GOV Y ACFT SPOTTED VISUALLY. STARTED DSCNT AND ADVISED ZFW. AT FL257 GOV Y OBSERVED DSNDING AS TCASII COMMANDED A CLB. KEPT GOV Y VISUAL AND CLBED BACK TO FL260.

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.