Narrative:

Air carrier X was sbound J53 at FL310 already handed off to next sector. Air carrier Y coming from same sector was northbound at FL330. (Air carrier should have been descending to FL290 from previous sector.) that sector coordinated with me that air carrier Y was my control reference other aircraft. I had tried to repos air carrier X data block but missed the first number in the computer entry. The data block then dropped off my scope. I was busy spacing pittsburgh arrs and didn't realize air carrier X data block was gone. As soon as air carrier Y checked on frequency I descended him to FL250 over top of air carrier X. He descended slowly and the data blocks went into conflict alert. (They were overlapping at the time.) by the time I repositioned the data blocks to see what was happening, air carrier Y was already in descent just north of air carrier X. I asked air carrier Y altitude. He said FL326. I then climbed air carrier Y back to FL330. The main contributing factor was not having air carrier X data block on my scope. I didn't realize where air carrier X was when I descended the jet because of the missing data block. Secondary factor was the sector handing off air carrier Y to me did not have air carrier descending to FL290 forcing me to deal with the situation.

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Original NASA ASRS Text

Title: ACR Y DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR X. SYS ERROR.

Narrative: ACR X WAS SBOUND J53 AT FL310 ALREADY HANDED OFF TO NEXT SECTOR. ACR Y COMING FROM SAME SECTOR WAS NBOUND AT FL330. (ACR SHOULD HAVE BEEN DSNDING TO FL290 FROM PREVIOUS SECTOR.) THAT SECTOR COORDINATED WITH ME THAT ACR Y WAS MY CTL REF OTHER ACFT. I HAD TRIED TO REPOS ACR X DATA BLOCK BUT MISSED THE FIRST NUMBER IN THE COMPUTER ENTRY. THE DATA BLOCK THEN DROPPED OFF MY SCOPE. I WAS BUSY SPACING PITTSBURGH ARRS AND DIDN'T REALIZE ACR X DATA BLOCK WAS GONE. AS SOON AS ACR Y CHKED ON FREQ I DSNDED HIM TO FL250 OVER TOP OF ACR X. HE DSNDED SLOWLY AND THE DATA BLOCKS WENT INTO CONFLICT ALERT. (THEY WERE OVERLAPPING AT THE TIME.) BY THE TIME I REPOSITIONED THE DATA BLOCKS TO SEE WHAT WAS HAPPENING, ACR Y WAS ALREADY IN DSCNT JUST N OF ACR X. I ASKED ACR Y ALT. HE SAID FL326. I THEN CLBED ACR Y BACK TO FL330. THE MAIN CONTRIBUTING FACTOR WAS NOT HAVING ACR X DATA BLOCK ON MY SCOPE. I DIDN'T REALIZE WHERE ACR X WAS WHEN I DSNDED THE JET BECAUSE OF THE MISSING DATA BLOCK. SECONDARY FACTOR WAS THE SECTOR HANDING OFF ACR Y TO ME DID NOT HAVE ACR DSNDING TO FL290 FORCING ME TO DEAL WITH THE SIT.

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.