Narrative:

Controller accepted handoff on aircraft X, inbound to cmn who was head-on with air carrier Y. Aircraft X called on, at FL310, and controller overlooked air carrier Y and descended aircraft X into acby. Controller tried to rescind clearance to aircraft X, but aircraft had already left FL310. Human error.

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Original NASA ASRS Text

Title: ZID SUPVR OBSERVED OPERROR AT FL300.

Narrative: CTLR ACCEPTED HDOF ON ACFT X, INBOUND TO CMN WHO WAS HEAD-ON WITH ACR Y. ACFT X CALLED ON, AT FL310, AND CTLR OVERLOOKED ACR Y AND DSNDED ACFT X INTO ACBY. CTLR TRIED TO RESCIND CLRNC TO ACFT X, BUT ACFT HAD ALREADY LEFT FL310. HUMAN ERROR.

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.