Narrative:

I was training on 2 combined radar sectors. The conquest was released from lgb and took off on the assigned heading of 200 degrees climbing to 3000 ft. I adjusted the heading to 180 degrees as with most jet departures. My trainer and I began to discuss how the heading of 200 degrees was better for various reasons. The C172 was tracking wbound on a heading to join a radial at 4000 ft. Since I needed to climb the conquest; I issued traffic; which he reported in sight; and I instructed him to maintain visual separation; which he accepted. I issued traffic to the C172; which he also reported in sight. There was another VFR target at 3500 ft; which I observed; tracking eastbound; that must have been on the C425's TCAS; because he said he would hold 2400 ft briefly. I did not understand why; and reiterated the climb to 7000 ft; since the traffic was not a factor. He began to climb toward the wbound C172; and I became alarmed when the targets of the C425 and C172 appeared to be merging rapidly and near the same altitude. My instructor said; 'classic case of seeing the wrong one.' I started to key; but by then it was too late. Both aircraft were showing 4000 ft when the targets merged. Then the xponders canceled; and I was sure that they hit. On the next sweep; the C425 was at 4300 ft and the C172 was at 3700 ft and deviating swbound. By some miracle; they missed. I am shaking as I write this. Everything else went routinely; but I learned a few things. First; visual separation at night is bad because of the confusion that can easily occur if there is other traffic nearby. Second; I should have continued vertical separation until I was certain that he had the correct airplane in sight. Even though the traffic was issued as 'wbound;' I sometimes confuse the two (as do all atcs at times). Third; since the C425 had accepted visual separation; it was technically his fault if they hit; but I cannot help but feeling that I was a contributing factor. All in all; it was a great learning experience that I hope never to see again.

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Original NASA ASRS Text

Title: SCT DEV CTLR DESCRIBED NMAC WHEN AN IFR ACFT; ISSUED VISUAL SEPARATION CLIMB CLRNC BUT SEEING WRONG ACFT; CONFLICTED WITH ANOTHER IFR ACFT.

Narrative: I WAS TRAINING ON 2 COMBINED RADAR SECTORS. THE CONQUEST WAS RELEASED FROM LGB AND TOOK OFF ON THE ASSIGNED HDG OF 200 DEGS CLBING TO 3000 FT. I ADJUSTED THE HDG TO 180 DEGS AS WITH MOST JET DEPS. MY TRAINER AND I BEGAN TO DISCUSS HOW THE HDG OF 200 DEGS WAS BETTER FOR VARIOUS REASONS. THE C172 WAS TRACKING WBOUND ON A HDG TO JOIN A RADIAL AT 4000 FT. SINCE I NEEDED TO CLB THE CONQUEST; I ISSUED TFC; WHICH HE RPTED IN SIGHT; AND I INSTRUCTED HIM TO MAINTAIN VISUAL SEPARATION; WHICH HE ACCEPTED. I ISSUED TFC TO THE C172; WHICH HE ALSO RPTED IN SIGHT. THERE WAS ANOTHER VFR TARGET AT 3500 FT; WHICH I OBSERVED; TRACKING EBOUND; THAT MUST HAVE BEEN ON THE C425'S TCAS; BECAUSE HE SAID HE WOULD HOLD 2400 FT BRIEFLY. I DID NOT UNDERSTAND WHY; AND REITERATED THE CLB TO 7000 FT; SINCE THE TFC WAS NOT A FACTOR. HE BEGAN TO CLB TOWARD THE WBOUND C172; AND I BECAME ALARMED WHEN THE TARGETS OF THE C425 AND C172 APPEARED TO BE MERGING RAPIDLY AND NEAR THE SAME ALT. MY INSTRUCTOR SAID; 'CLASSIC CASE OF SEEING THE WRONG ONE.' I STARTED TO KEY; BUT BY THEN IT WAS TOO LATE. BOTH ACFT WERE SHOWING 4000 FT WHEN THE TARGETS MERGED. THEN THE XPONDERS CANCELED; AND I WAS SURE THAT THEY HIT. ON THE NEXT SWEEP; THE C425 WAS AT 4300 FT AND THE C172 WAS AT 3700 FT AND DEVIATING SWBOUND. BY SOME MIRACLE; THEY MISSED. I AM SHAKING AS I WRITE THIS. EVERYTHING ELSE WENT ROUTINELY; BUT I LEARNED A FEW THINGS. FIRST; VISUAL SEPARATION AT NIGHT IS BAD BECAUSE OF THE CONFUSION THAT CAN EASILY OCCUR IF THERE IS OTHER TFC NEARBY. SECOND; I SHOULD HAVE CONTINUED VERT SEPARATION UNTIL I WAS CERTAIN THAT HE HAD THE CORRECT AIRPLANE IN SIGHT. EVEN THOUGH THE TFC WAS ISSUED AS 'WBOUND;' I SOMETIMES CONFUSE THE TWO (AS DO ALL ATCS AT TIMES). THIRD; SINCE THE C425 HAD ACCEPTED VISUAL SEPARATION; IT WAS TECHNICALLY HIS FAULT IF THEY HIT; BUT I CANNOT HELP BUT FEELING THAT I WAS A CONTRIBUTING FACTOR. ALL IN ALL; IT WAS A GREAT LEARNING EXPERIENCE THAT I HOPE NEVER TO SEE AGAIN.

Data retrieved from NASA's ASRS site as of January 2009 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.