Narrative:

I had been working for 1 hour and 50 mins in a continuous moderate to busy phase. Air carrier X was wbound at FL300. Air carrier Y was about 15 mi west of air carrier X and about 2 mi south of air carrier X route at FL310 eastbound. Air carrier Y needed to begin his descent into pit. I looked for traffic out in front of air carrier Y to see what altitude I could start him down to. I overlooked air carrier X and believed that FL280 was an available altitude for air carrier Y. I issued the descent and continued my scan and issuing other clrncs to other aircraft under my control. The sector team then saw the confliction with air carrier X. Air carrier Y was issued to maintain FL310 and turned 40 degrees right. While the clearance was issued; air carrier Y started his descent and separation was lost. The aircraft passed approximately 2.5 mi laterally and 700 ft vertically. I do believe that due to the long period of time working continuous moderate/busy traffic led to me feeling somewhat exhausted and why the traffic was overlooked.

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Original NASA ASRS Text

Title: ZME CTLR EXPERIENCED OPERROR AT FL300 WHEN ISSUING A DSCNT CLRNC AND FAILED TO OBSERVE HEAD-ON TFC AT LOWER ALT.

Narrative: I HAD BEEN WORKING FOR 1 HR AND 50 MINS IN A CONTINUOUS MODERATE TO BUSY PHASE. ACR X WAS WBOUND AT FL300. ACR Y WAS ABOUT 15 MI W OF ACR X AND ABOUT 2 MI S OF ACR X RTE AT FL310 EBOUND. ACR Y NEEDED TO BEGIN HIS DSCNT INTO PIT. I LOOKED FOR TFC OUT IN FRONT OF ACR Y TO SEE WHAT ALT I COULD START HIM DOWN TO. I OVERLOOKED ACR X AND BELIEVED THAT FL280 WAS AN AVAILABLE ALT FOR ACR Y. I ISSUED THE DSCNT AND CONTINUED MY SCAN AND ISSUING OTHER CLRNCS TO OTHER ACFT UNDER MY CTL. THE SECTOR TEAM THEN SAW THE CONFLICTION WITH ACR X. ACR Y WAS ISSUED TO MAINTAIN FL310 AND TURNED 40 DEGS R. WHILE THE CLRNC WAS ISSUED; ACR Y STARTED HIS DSCNT AND SEPARATION WAS LOST. THE ACFT PASSED APPROX 2.5 MI LATERALLY AND 700 FT VERTICALLY. I DO BELIEVE THAT DUE TO THE LONG PERIOD OF TIME WORKING CONTINUOUS MODERATE/BUSY TFC LED TO ME FEELING SOMEWHAT EXHAUSTED AND WHY THE TFC WAS OVERLOOKED.

Data retrieved from NASA's ASRS site as of January 2009 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.