Narrative:

The F100 is inbound to bna from the east, filed over vxv, but has been deviating north of course around thunderstorm activity, now proceeding direct volls for the volls arrival. The F100 was cleared to FL240, and the handoff was initiated to the next sector. I then indicated a possible confliction for the aircraft with the MD80, which was proceeding sebound toward vxv and descending from FL270 to FL250. I had in mind that we might force the F100 down to FL240 more quickly to get under the MD80 (they were still about 3-4 mins apart). The radar controller elected to stop the F100 at FL260 above the descending MD80, which seemed like a completely valid plan. The 2 aircraft are on different frequencys (their crossing point is close to the sector boundary, which is a north/south line). Each aircraft has been handed off to the next sector, but is still on the previous sector's frequency. Because the F100 was originally cleared to FL240, the data block for that aircraft indicated that the F100 was descending to FL240 even though the aircraft had been stopped off at FL260. Since the data block had already been handed off to the next sector, it was not corrected to indicate that the aircraft was actually only descending to FL260. I did not contact the other controller to advise them that the F100 was stopping at FL260. (Since the confliction would happen in our sector, we intended to separate the aircraft, at FL250 and FL260, and they resume the F100's descent to FL240, as indicated in the data block.) the radar controller at the adjacent sector was preparing to switch the MD80 to our frequency and noticed that the F100 was not yet below his MD80 descending to FL250. (Remember, he did not know that we had stopped the F100 at FL260.) although his MD80 was descending rapidly, he attempted to stop the MD80 at FL260, which he expected to be above our aircraft descending to FL240. Without checking with us first, he cleared the MD80 to climb back to FL260 (it had almost leveled at FL250). He thought he was helping us separate the 2 aircraft, but had just the opposite effect. Once he realized that the F100 was not descending, he turned the MD80 away from the F100 and contacted us to discuss what to do. Both aircraft were then turned further away from each other, and we started the F100 down to FL240, but our actions were not able to prevent a loss of separation. As far as I can tell, TCASII did not go off, and the pilots did not take any evasive action except as instructed by ATC. At least one of the other pilots (the F100) saw the other aircraft. Since the 2 aircraft were conflicting inside our airspace, I did not see any need for me to advise the next sector that the F100 was not descending to FL240. After all, we were responsible for separation, not the next guy, but my thinking on this failed to anticipate that the next controller might take unexpected action based on what he thought was an imminent loss of separation. In retrospect, it is obvious that I need to give more consideration to what other controllers may do and make sure they have all the information needed to make good decisions.

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Original NASA ASRS Text

Title: ZTL HDOF CTLR EXPLAINS REASONS FOR OPERROR WITH ADJACENT CTL SECTOR.

Narrative: THE F100 IS INBOUND TO BNA FROM THE E, FILED OVER VXV, BUT HAS BEEN DEVIATING N OF COURSE AROUND TSTM ACTIVITY, NOW PROCEEDING DIRECT VOLLS FOR THE VOLLS ARR. THE F100 WAS CLRED TO FL240, AND THE HDOF WAS INITIATED TO THE NEXT SECTOR. I THEN INDICATED A POSSIBLE CONFLICTION FOR THE ACFT WITH THE MD80, WHICH WAS PROCEEDING SEBOUND TOWARD VXV AND DSNDING FROM FL270 TO FL250. I HAD IN MIND THAT WE MIGHT FORCE THE F100 DOWN TO FL240 MORE QUICKLY TO GET UNDER THE MD80 (THEY WERE STILL ABOUT 3-4 MINS APART). THE RADAR CTLR ELECTED TO STOP THE F100 AT FL260 ABOVE THE DSNDING MD80, WHICH SEEMED LIKE A COMPLETELY VALID PLAN. THE 2 ACFT ARE ON DIFFERENT FREQS (THEIR XING POINT IS CLOSE TO THE SECTOR BOUNDARY, WHICH IS A N/S LINE). EACH ACFT HAS BEEN HANDED OFF TO THE NEXT SECTOR, BUT IS STILL ON THE PREVIOUS SECTOR'S FREQ. BECAUSE THE F100 WAS ORIGINALLY CLRED TO FL240, THE DATA BLOCK FOR THAT ACFT INDICATED THAT THE F100 WAS DSNDING TO FL240 EVEN THOUGH THE ACFT HAD BEEN STOPPED OFF AT FL260. SINCE THE DATA BLOCK HAD ALREADY BEEN HANDED OFF TO THE NEXT SECTOR, IT WAS NOT CORRECTED TO INDICATE THAT THE ACFT WAS ACTUALLY ONLY DSNDING TO FL260. I DID NOT CONTACT THE OTHER CTLR TO ADVISE THEM THAT THE F100 WAS STOPPING AT FL260. (SINCE THE CONFLICTION WOULD HAPPEN IN OUR SECTOR, WE INTENDED TO SEPARATE THE ACFT, AT FL250 AND FL260, AND THEY RESUME THE F100'S DSCNT TO FL240, AS INDICATED IN THE DATA BLOCK.) THE RADAR CTLR AT THE ADJACENT SECTOR WAS PREPARING TO SWITCH THE MD80 TO OUR FREQ AND NOTICED THAT THE F100 WAS NOT YET BELOW HIS MD80 DSNDING TO FL250. (REMEMBER, HE DID NOT KNOW THAT WE HAD STOPPED THE F100 AT FL260.) ALTHOUGH HIS MD80 WAS DSNDING RAPIDLY, HE ATTEMPTED TO STOP THE MD80 AT FL260, WHICH HE EXPECTED TO BE ABOVE OUR ACFT DSNDING TO FL240. WITHOUT CHKING WITH US FIRST, HE CLRED THE MD80 TO CLB BACK TO FL260 (IT HAD ALMOST LEVELED AT FL250). HE THOUGHT HE WAS HELPING US SEPARATE THE 2 ACFT, BUT HAD JUST THE OPPOSITE EFFECT. ONCE HE REALIZED THAT THE F100 WAS NOT DSNDING, HE TURNED THE MD80 AWAY FROM THE F100 AND CONTACTED US TO DISCUSS WHAT TO DO. BOTH ACFT WERE THEN TURNED FURTHER AWAY FROM EACH OTHER, AND WE STARTED THE F100 DOWN TO FL240, BUT OUR ACTIONS WERE NOT ABLE TO PREVENT A LOSS OF SEPARATION. AS FAR AS I CAN TELL, TCASII DID NOT GO OFF, AND THE PLTS DID NOT TAKE ANY EVASIVE ACTION EXCEPT AS INSTRUCTED BY ATC. AT LEAST ONE OF THE OTHER PLTS (THE F100) SAW THE OTHER ACFT. SINCE THE 2 ACFT WERE CONFLICTING INSIDE OUR AIRSPACE, I DID NOT SEE ANY NEED FOR ME TO ADVISE THE NEXT SECTOR THAT THE F100 WAS NOT DSNDING TO FL240. AFTER ALL, WE WERE RESPONSIBLE FOR SEPARATION, NOT THE NEXT GUY, BUT MY THINKING ON THIS FAILED TO ANTICIPATE THAT THE NEXT CTLR MIGHT TAKE UNEXPECTED ACTION BASED ON WHAT HE THOUGHT WAS AN IMMINENT LOSS OF SEPARATION. IN RETROSPECT, IT IS OBVIOUS THAT I NEED TO GIVE MORE CONSIDERATION TO WHAT OTHER CTLRS MAY DO AND MAKE SURE THEY HAVE ALL THE INFO NEEDED TO MAKE GOOD DECISIONS.

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.