Narrative:

Aircraft #1 was level FL350 en route gsh direct dsm aircraft #2 was level FL330 en route alo direct low then southeast. Clearance was given to aircraft #1 to descend to FL330. When he started down he was changed to the next frequency. Shortly thereafter the potential conflict was noticed. I went to the sector controling #1 and told the controller to climb back to FL350. At the same time I checked his scope (he owned FL310 and below and I owned FL330 and above) to make sure FL310 was clear. I then descended aircraft #2. The cause of the problem was my failure to notice the potential conflict. This was compounded by the aircraft being on different frequencys.

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Original NASA ASRS Text

Title: LTSS BTWN ACFT X AND ACFT Y. SYS ERROR.

Narrative: ACFT #1 WAS LEVEL FL350 ENRTE GSH DIRECT DSM ACFT #2 WAS LEVEL FL330 ENRTE ALO DIRECT LOW THEN SE. CLRNC WAS GIVEN TO ACFT #1 TO DSND TO FL330. WHEN HE STARTED DOWN HE WAS CHANGED TO THE NEXT FREQ. SHORTLY THEREAFTER THE POTENTIAL CONFLICT WAS NOTICED. I WENT TO THE SECTOR CTLING #1 AND TOLD THE CTLR TO CLB BACK TO FL350. AT THE SAME TIME I CHKED HIS SCOPE (HE OWNED FL310 AND BELOW AND I OWNED FL330 AND ABOVE) TO MAKE SURE FL310 WAS CLR. I THEN DSNDED ACFT #2. THE CAUSE OF THE PROB WAS MY FAILURE TO NOTICE THE POTENTIAL CONFLICT. THIS WAS COMPOUNDED BY THE ACFT BEING ON DIFFERENT FREQS.

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.