Narrative:

The sector was moderate or greater volume with moderate complexity, which is routine for the sector at this time of day. I did not have a tracker (coordinator) at the sector because the sector still seemed manageable and I felt like the sector 'plan' for the aircraft we already had was workable. The astra was sbound over vxv VORTAC and was landing at an airport in the atlanta terminal area. Our normal procedure for these aircraft is to have them at or below FL330, descending to FL240 by 25 mi south of vxv. The E145 was nebound (J22.vxv.J91) and both aircraft were level at FL330. Since the astra would have to descend soon anyway, I resolved the confliction by clearing the astra to FL290. This was 4 or 5 mins prior to the confliction point. Since I only needed to have the aircraft descend 2000 ft in 4 (or more) mins, I did not think that it would be necessary to give a crossing restr (even a 500 FPM descent rate would be enough to achieve separation). However, the pilot did not descend the aircraft at more than about 400 FPM, and I was so busy with other aircraft conflictions that I failed to observe the aircraft's slow descent. The conflict alert activated as the aircraft lost separation, but since the aircraft were already past one another, I did not initiate any evasive action.

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Original NASA ASRS Text

Title: ZTL CTLR OVERLOOKS KNOWN CONFLICT WITH A SLOW DSNDING ASTRA AND AN ENRTE EMB145.

Narrative: THE SECTOR WAS MODERATE OR GREATER VOLUME WITH MODERATE COMPLEXITY, WHICH IS ROUTINE FOR THE SECTOR AT THIS TIME OF DAY. I DID NOT HAVE A TRACKER (COORDINATOR) AT THE SECTOR BECAUSE THE SECTOR STILL SEEMED MANAGEABLE AND I FELT LIKE THE SECTOR 'PLAN' FOR THE ACFT WE ALREADY HAD WAS WORKABLE. THE ASTRA WAS SBOUND OVER VXV VORTAC AND WAS LNDG AT AN ARPT IN THE ATLANTA TERMINAL AREA. OUR NORMAL PROC FOR THESE ACFT IS TO HAVE THEM AT OR BELOW FL330, DSNDING TO FL240 BY 25 MI S OF VXV. THE E145 WAS NEBOUND (J22.VXV.J91) AND BOTH ACFT WERE LEVEL AT FL330. SINCE THE ASTRA WOULD HAVE TO DSND SOON ANYWAY, I RESOLVED THE CONFLICTION BY CLRING THE ASTRA TO FL290. THIS WAS 4 OR 5 MINS PRIOR TO THE CONFLICTION POINT. SINCE I ONLY NEEDED TO HAVE THE ACFT DSND 2000 FT IN 4 (OR MORE) MINS, I DID NOT THINK THAT IT WOULD BE NECESSARY TO GIVE A XING RESTR (EVEN A 500 FPM DSCNT RATE WOULD BE ENOUGH TO ACHIEVE SEPARATION). HOWEVER, THE PLT DID NOT DSND THE ACFT AT MORE THAN ABOUT 400 FPM, AND I WAS SO BUSY WITH OTHER ACFT CONFLICTIONS THAT I FAILED TO OBSERVE THE ACFT'S SLOW DSCNT. THE CONFLICT ALERT ACTIVATED AS THE ACFT LOST SEPARATION, BUT SINCE THE ACFT WERE ALREADY PAST ONE ANOTHER, I DID NOT INITIATE ANY EVASIVE ACTION.

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.