Narrative:

I was working FR1/FR2. In the decombination briefing I gave up the east final (FR2) and kept the west final (FR1). The traffic portion of the decombination briefing included a B757 on visual approach for runway 35R at 3;000 ft already talking to the tower; with the SH33 on a base leg heading of 255 degrees at 4;000 ft; setting him up to follow the B757. The SH33 did not yet have the traffic in sight to follow him. The A306 was on the final for runway 35L at 4;000 ft; cleared on the ILS approach. The positions were decombined at this point; and I failed to realize that SH33 needed to be switched to the east final frequency. I went back to working the rest of my aircraft on the west side. The east final controller asked me if SH33 was turning to join the localizer for 35R; and it was then that I realized my mistake. The SH33 was at the same altitude as the A306; and even though his heading was such that he would pass behind the A306; there would not have been appropriate wake turbulence separation with the small behind the large. I called the traffic to the SH33; who had the A306 in sight and maintained visual separation; and then cleared him on the visual approach to runway 35R. I then called the traffic to A306; who had the SH33 in sight and maintained visual separation on their respective final approach course. I should have ensured that the frequency change was completed after the briefing that would have saved all the trouble of this incident. I would like to point out that the collision alert alarm never did go off; [which] would also have drawn my attention to the developing situation.

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Original NASA ASRS Text

Title: SDF Controllers described a loss of separation event occurring shortly after final positions were decombined; the controller working the combined positions electing to retain the conflicting traffic on his/her frequency.

Narrative: I was working FR1/FR2. In the decombination briefing I gave up the East Final (FR2) and kept the West Final (FR1). The traffic portion of the decombination briefing included a B757 on visual approach for Runway 35R at 3;000 FT already talking to the Tower; with the SH33 on a base leg heading of 255 degrees at 4;000 FT; setting him up to follow the B757. The SH33 did not yet have the traffic in sight to follow him. The A306 was on the final for Runway 35L at 4;000 FT; cleared on the ILS Approach. The positions were decombined at this point; and I failed to realize that SH33 needed to be switched to the East Final Frequency. I went back to working the rest of my aircraft on the west side. The East Final Controller asked me if SH33 was turning to join the localizer for 35R; and it was then that I realized my mistake. The SH33 was at the same altitude as the A306; and even though his heading was such that he would pass behind the A306; there would not have been appropriate wake turbulence separation with the small behind the large. I called the traffic to the SH33; who had the A306 in sight and maintained visual separation; and then cleared him on the visual approach to Runway 35R. I then called the traffic to A306; who had the SH33 in sight and maintained visual separation on their respective final approach course. I should have ensured that the frequency change was completed after the briefing that would have saved all the trouble of this incident. I would like to point out that the Collision Alert alarm never did go off; [which] would also have drawn my attention to the developing situation.

Data retrieved from NASA's ASRS site as of April 2012 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.