Narrative:

Aircraft Y, swbound to atl, assigned present heading. Aircraft X, wswbound to dfw, assigned 295 degree heading for vector to go behind aircraft Y. Both aircraft at FL310. I asked aircraft Y what his heading was. I understood him to say '2-0-5.' I then assigned aircraft Y nearing '2-1-5,' thinking it was a right turn of 10 degrees. I watched history of aircraft Y begin to track to the left and subsequently assigned aircraft Y to fly 225 degree heading and descend to FL290. I assigned aircraft X to fly heading 350 degrees. Separation was lost at 4.2 mi. Aircraft Y was FL295 and aircraft X at FL310. After the investigation, the taped transmission showed that aircraft Y had responded '2-5-0' when asked about his heading. When I assigned heading 215 degrees, thinking it was a right turn of 10 degrees, it was actually a left turn of 35 degrees.

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Original NASA ASRS Text

Title: ZID CTLR EXPERIENCED OPERROR INVOLVING TWO ENRTE ACFT AT FL310.

Narrative: ACFT Y, SWBOUND TO ATL, ASSIGNED PRESENT HEADING. ACFT X, WSWBOUND TO DFW, ASSIGNED 295 DEG HDG FOR VECTOR TO GO BEHIND ACFT Y. BOTH ACFT AT FL310. I ASKED ACFT Y WHAT HIS HEADING WAS. I UNDERSTOOD HIM TO SAY '2-0-5.' I THEN ASSIGNED ACFT Y NEARING '2-1-5,' THINKING IT WAS A R TURN OF 10 DEGS. I WATCHED HISTORY OF ACFT Y BEGIN TO TRACK TO THE L AND SUBSEQUENTLY ASSIGNED ACFT Y TO FLY 225 DEG HDG AND DSND TO FL290. I ASSIGNED ACFT X TO FLY HEADING 350 DEGS. SEPARATION WAS LOST AT 4.2 MI. ACFT Y WAS FL295 AND ACFT X AT FL310. AFTER THE INVESTIGATION, THE TAPED XMISSION SHOWED THAT ACFT Y HAD RESPONDED '2-5-0' WHEN ASKED ABOUT HIS HEADING. WHEN I ASSIGNED HEADING 215 DEGS, THINKING IT WAS A R TURN OF 10 DEGS, IT WAS ACTUALLY A L TURN OF 35 DEGS.

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.