Narrative:

Aircraft Y was at FL210. When I took the handoff, aircraft Y was right on top of air carrier X at FL200, who I knew would outrun aircraft Y, so I knew I would be able to get aircraft Y down to 16000 ft for the next sector. When aircraft Y entered my airspace, I issued clearance to cross alb VOR at 16000 ft. At this time, I believed aircraft Y was below air carrier X who was behind him and overtaking him at FL200 this was my error. I do not recall if I thought aircraft Y and air carrier X altitudes were reversed or if I looked quickly at air carrier X's full data block and interpreted the altitude as FL220 instead of FL200 or if the for whatever reason, I didn't realize my error until aircraft Y's mode C indicated FL207 and air carrier X's mode C indicated FL195. At this time, I tried to separate the aircraft as much as possible, even though I knew I had already lost separation. I tried to stop aircraft Y at FL210, but it was too late. I turned air carrier X to a 270 degree heading and issued FL180. I tried to stop aircraft Y at FL200 and FL190 but he just kept descending. Air carrier X later said he received an RA and that's why he descended originally when aircraft Y left FL210. Aircraft Y was also TCASII equipped, but there is no evidence that it was ever given an advisory. Supplemental information from acn 488834: I was unaware of an operational error until the radar controller had taken action, and the operational error had already occurred.

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Original NASA ASRS Text

Title: ZBW CTLR TRANSPOSES DC9 AND BE30 ALT ASSIGNMENTS, DSNDS THE WRONG ACFT, CAUSING A CONFLICT.

Narrative: ACFT Y WAS AT FL210. WHEN I TOOK THE HDOF, ACFT Y WAS RIGHT ON TOP OF ACR X AT FL200, WHO I KNEW WOULD OUTRUN ACFT Y, SO I KNEW I WOULD BE ABLE TO GET ACFT Y DOWN TO 16000 FT FOR THE NEXT SECTOR. WHEN ACFT Y ENTERED MY AIRSPACE, I ISSUED CLRNC TO CROSS ALB VOR AT 16000 FT. AT THIS TIME, I BELIEVED ACFT Y WAS BELOW ACR X WHO WAS BEHIND HIM AND OVERTAKING HIM AT FL200 THIS WAS MY ERROR. I DO NOT RECALL IF I THOUGHT ACFT Y AND ACR X ALTS WERE REVERSED OR IF I LOOKED QUICKLY AT ACR X'S FULL DATA BLOCK AND INTERPED THE ALT AS FL220 INSTEAD OF FL200 OR IF THE FOR WHATEVER REASON, I DIDN'T REALIZE MY ERROR UNTIL ACFT Y'S MODE C INDICATED FL207 AND ACR X'S MODE C INDICATED FL195. AT THIS TIME, I TRIED TO SEPARATE THE ACFT AS MUCH AS POSSIBLE, EVEN THOUGH I KNEW I HAD ALREADY LOST SEPARATION. I TRIED TO STOP ACFT Y AT FL210, BUT IT WAS TOO LATE. I TURNED ACR X TO A 270 DEG HDG AND ISSUED FL180. I TRIED TO STOP ACFT Y AT FL200 AND FL190 BUT HE JUST KEPT DSNDING. ACR X LATER SAID HE RECEIVED AN RA AND THAT'S WHY HE DSNDED ORIGINALLY WHEN ACFT Y LEFT FL210. ACFT Y WAS ALSO TCASII EQUIPPED, BUT THERE IS NO EVIDENCE THAT IT WAS EVER GIVEN AN ADVISORY. SUPPLEMENTAL INFO FROM ACN 488834: I WAS UNAWARE OF AN OPERROR UNTIL THE RADAR CTLR HAD TAKEN ACTION, AND THE OPERROR HAD ALREADY OCCURRED.

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.