Narrative:

I was working final radar at cvg approach. It was the tail end of an arrival push and I started to relax. Small aircraft X was inbound to runway 18R from the northeast on a left base descending from 6000 to 2500 and air carrier Y was on a left downwind descending to 4000. For some reason I believed that the small aircraft X was already below 3000. Suddenly I noticed the aircraft about 3 mi apart and converging with only 300 ft between them. I told small aircraft X to expedite its descent and told air carrier Y to stop descent. I issued traffic at 12 O'clock, 2 mi descending out of 4000. Air carrier Y later reported that he saw small aircraft X and that his TCASII had alerted him to its position. I learned not to relax until I am relieved from the position and don't depend on what I believe to be true, without verifying it.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR Y HAD LTSS FROM SMA X. SYS ERROR. TCASII TA.

Narrative: I WAS WORKING FINAL RADAR AT CVG APCH. IT WAS THE TAIL END OF AN ARR PUSH AND I STARTED TO RELAX. SMA X WAS INBOUND TO RWY 18R FROM THE NE ON A L BASE DSNDING FROM 6000 TO 2500 AND ACR Y WAS ON A L DOWNWIND DSNDING TO 4000. FOR SOME REASON I BELIEVED THAT THE SMA X WAS ALREADY BELOW 3000. SUDDENLY I NOTICED THE ACFT ABOUT 3 MI APART AND CONVERGING WITH ONLY 300 FT BTWN THEM. I TOLD SMA X TO EXPEDITE ITS DSCNT AND TOLD ACR Y TO STOP DSCNT. I ISSUED TFC AT 12 O'CLOCK, 2 MI DSNDING OUT OF 4000. ACR Y LATER RPTED THAT HE SAW SMA X AND THAT HIS TCASII HAD ALERTED HIM TO ITS POS. I LEARNED NOT TO RELAX UNTIL I AM RELIEVED FROM THE POS AND DON'T DEPEND ON WHAT I BELIEVE TO BE TRUE, WITHOUT VERIFYING IT.

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.