Narrative:

This event involved small transport X at 13000' from cje to buy and cpr Y at 12000' from 4w8 to cha. I was the radar controller at sector 29 at atlanta center. Small transport X checked in at FL130 requesting lower. I cleared small transport X to turn left to heading 065 for descent, about a 60 degree turn. Small transport X immediately cancelled IFR due to the sector complexity at the time, I terminated small transport X and did not offer advisories. Shortly after I turned cpr Y on course, (he was on a heading for traffic). Although I didn't recognize it at the time, this in effect put small transport X and cpr Y head on to each other. I first noticed the conflict when the aircraft were about 10 mi apart. Small transport X, now squawking VFR and off frequency was at 12800' descending. Cpr Y was level at 12000'. I called traffic to cpr Y approximately 3 times. Cpr Y never picked up the traffic. When I thought the aircraft were going to hit I suggested cpr Y turn 90 degrees right immediately. Cpr Y took the turn. The targets merged, both mode C readouts indicating 12000' at the time. Cpr Y never saw small transport X. Small transport X never called so I assume he didn't see cpr Y either.

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Original NASA ASRS Text

Title: IMC CPR Y HAD NMAC WITH VMC SMT X. SEE AND AVOID CONCEPT.

Narrative: THIS EVENT INVOLVED SMT X AT 13000' FROM CJE TO BUY AND CPR Y AT 12000' FROM 4W8 TO CHA. I WAS THE RADAR CTLR AT SECTOR 29 AT ATLANTA CTR. SMT X CHKED IN AT FL130 REQUESTING LOWER. I CLRED SMT X TO TURN L TO HDG 065 FOR DSNT, ABOUT A 60 DEG TURN. SMT X IMMEDIATELY CANCELLED IFR DUE TO THE SECTOR COMPLEXITY AT THE TIME, I TERMINATED SMT X AND DID NOT OFFER ADVISORIES. SHORTLY AFTER I TURNED CPR Y ON COURSE, (HE WAS ON A HDG FOR TFC). ALTHOUGH I DIDN'T RECOGNIZE IT AT THE TIME, THIS IN EFFECT PUT SMT X AND CPR Y HEAD ON TO EACH OTHER. I FIRST NOTICED THE CONFLICT WHEN THE ACFT WERE ABOUT 10 MI APART. SMT X, NOW SQUAWKING VFR AND OFF FREQ WAS AT 12800' DSNDING. CPR Y WAS LEVEL AT 12000'. I CALLED TFC TO CPR Y APPROX 3 TIMES. CPR Y NEVER PICKED UP THE TFC. WHEN I THOUGHT THE ACFT WERE GOING TO HIT I SUGGESTED CPR Y TURN 90 DEGS R IMMEDIATELY. CPR Y TOOK THE TURN. THE TARGETS MERGED, BOTH MODE C READOUTS INDICATING 12000' AT THE TIME. CPR Y NEVER SAW SMT X. SMT X NEVER CALLED SO I ASSUME HE DIDN'T SEE CPR Y EITHER.

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.