Narrative:

Aircraft #1 (aircraft X) was swbound on FL350, aircraft #2 (aircraft Y) was nwbound at FL350. I assumed that there would be at least 5 mi between them and upon realizing that there would be less, I descended aircraft Y but separation was already lost.

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Original NASA ASRS Text

Title: RPTR ASSUMED THAT ACFT X AND Y WOULD PASS EACH OTHER WITH LEGAL SEPARATION. RPTR REALIZING THAT SEPARATION WAS INADEQUATE, TRIED TO RECOVER, BUT NOT SOON ENOUGH, RESULTED IN OPERROR.

Narrative: ACFT #1 (ACFT X) WAS SWBOUND ON FL350, ACFT #2 (ACFT Y) WAS NWBOUND AT FL350. I ASSUMED THAT THERE WOULD BE AT LEAST 5 MI BTWN THEM AND UPON REALIZING THAT THERE WOULD BE LESS, I DSNDED ACFT Y BUT SEPARATION WAS ALREADY LOST.

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.