Narrative:

I was working approach control at billings ATCT. Air carrier X was inbound northwest of the field. Air carrier a was southwest of the field on a vector for the visual approach. Aircraft Z departed runway heading. Aircraft Z is a twin cessna. Air carrier B departed behind the twin heading 310 degrees into the oncoming air carrier X. I turned air carrier X to a heading of 140 degrees; vector for opposite direction traffic. I then told aircraft Z about air carrier X. Their flight paths were converging; so I turned aircraft Z to a heading of 360 degrees and issued traffic. Air carrier Y departed runway 28R runway heading. I turned aircraft Z northbound for the faster traffic following aircraft Z. Aircraft Z and air carrier X were parallel each other; opposite direction. I stopped air carrier Y at 6000 ft for traffic. Air carrier X was stopped at 7000 ft. I then descended air carrier X to 6000 ft anticipating a turn and climb for air carrier Y. I cleared air carrier a for the visual approach and told him of the rj. I then told him to expedite his descent. Air carrier Y reported both air carrier X and air carrier a in sight. I climbed air carrier Y without telling him to maintain visual separation from air carrier X. Within 1 min or so the conflict alert went off between air carrier Y and air carrier X. When air carrier Y reported both aircraft; I believed he had them both in sight and that separation was maintained. That was until the conflict alert went off.

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Original NASA ASRS Text

Title: BIL APCH CTLR FAILED TO COMPLETE VISUAL SEPARATION APPLICATION RESULTING IN OPERROR BTWN 1 DEP AND 2 ARR ACFT.

Narrative: I WAS WORKING APCH CTL AT BILLINGS ATCT. ACR X WAS INBOUND NW OF THE FIELD. ACR A WAS SW OF THE FIELD ON A VECTOR FOR THE VISUAL APCH. ACFT Z DEPARTED RWY HDG. ACFT Z IS A TWIN CESSNA. ACR B DEPARTED BEHIND THE TWIN HDG 310 DEGS INTO THE ONCOMING ACR X. I TURNED ACR X TO A HDG OF 140 DEGS; VECTOR FOR OPPOSITE DIRECTION TFC. I THEN TOLD ACFT Z ABOUT ACR X. THEIR FLT PATHS WERE CONVERGING; SO I TURNED ACFT Z TO A HDG OF 360 DEGS AND ISSUED TFC. ACR Y DEPARTED RWY 28R RWY HDG. I TURNED ACFT Z NBOUND FOR THE FASTER TFC FOLLOWING ACFT Z. ACFT Z AND ACR X WERE PARALLEL EACH OTHER; OPPOSITE DIRECTION. I STOPPED ACR Y AT 6000 FT FOR TFC. ACR X WAS STOPPED AT 7000 FT. I THEN DSNDED ACR X TO 6000 FT ANTICIPATING A TURN AND CLB FOR ACR Y. I CLRED ACR A FOR THE VISUAL APCH AND TOLD HIM OF THE RJ. I THEN TOLD HIM TO EXPEDITE HIS DSCNT. ACR Y RPTED BOTH ACR X AND ACR A IN SIGHT. I CLBED ACR Y WITHOUT TELLING HIM TO MAINTAIN VISUAL SEPARATION FROM ACR X. WITHIN 1 MIN OR SO THE CONFLICT ALERT WENT OFF BTWN ACR Y AND ACR X. WHEN ACR Y RPTED BOTH ACFT; I BELIEVED HE HAD THEM BOTH IN SIGHT AND THAT SEPARATION WAS MAINTAINED. THAT WAS UNTIL THE CONFLICT ALERT WENT OFF.

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.