Narrative:

I was working the verde sector (south finals) with aircraft X; a B737. Simultaneous visual approaches were in progress to both runway 8 and 7R. I was sequencing straight in traffic with downwind traffic to runway 7R and provided my runway to a heavy KC35 inbound from the freeway sector (north finals). I sequenced the B737 off the downwind; to follow a heavy KC35 being worked by the freeway sector. I was trying to provide appropriate wake turbulence separation of 5 NM between the B737 and the heavy KC35 and so I waited until I had just over 6 miles before I turned the B737 and cleared him for the visual approach to runway 7R behind the KC35. The B737 turned slower than expected; and he overshot the 7R localizer and encroached upon the localizer for runway 8. This put them in conflict with an airbus being sequenced by the freeway sector to runway 8. I heard the freeway controller say the airbus had my B737 in sight and was instructed to maintain visual separation. My B737 corrected and reestablished themself on the runway 7R localizer and continued and completed their approach for runway 7R. The airbus did so as well. According to the 7110.65; I was 'okay' in this incident because I cleared my aircraft for a visual approach to runway 7R before separation was lost due to the fact that the runways 8 and 7R are more than 4300 ft apart. Aircraft came approximately 1 to 2 miles apart; but this was an unsafe situation due to my B737 overshooting the localizer. In retrospect; I should have turned the B737 to intercept and join the visual approach to runway 7R just a little bit sooner. I waited longer because I was trying to provide wake turbulence separation. The B737 did report the heavy KC35 in sight and was instructed to 'follow......caution wake turbulence'. Because of this incident; there was a 'snowball' effect; and two or three subsequent arrivals collapsed in regards to spacing. For the next two or three arrivals I had marginal separation and had to call the tower to request visual separation. The tower approved all requests for visual separation and stated that aircraft were 'in sight'. Recommendation; I would recommend that we stop being encouraged to 'swap' runways so much. I felt compelled to give my runway away during this scenario for the heavy KC35 being worked by freeway. If I did not give my runway away during this scenario; it would have not happened the way it did. It was a complex scenario because the KC35 had to cross the runway 8 final and 'hit a hole' in front of several of my straight in arrivals as well as a downwind aircraft. It helps if the other final controller realizes when requesting a 'swap' is going to cause undue hardship to the other final.

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Original NASA ASRS Text

Title: P50 Controller described a near loss of separation event during parallel arrival operations to Runways 8/7R; noting runway swaps to accommodate arrival traffic sometimes 'snowballs' into a more complex situation.

Narrative: I was working the VERDE Sector (South Finals) with aircraft X; a B737. Simultaneous visual approaches were in progress to both Runway 8 and 7R. I was sequencing straight in traffic with downwind traffic to Runway 7R and provided my runway to a Heavy KC35 inbound from the FREEWAY Sector (North Finals). I sequenced the B737 off the downwind; to follow a Heavy KC35 being worked by the FREEWAY Sector. I was trying to provide appropriate wake turbulence separation of 5 NM between the B737 and the Heavy KC35 and so I waited until I had just over 6 miles before I turned the B737 and cleared him for the visual approach to Runway 7R behind the KC35. The B737 turned slower than expected; and he overshot the 7R localizer and encroached upon the localizer for Runway 8. This put them in conflict with an Airbus being sequenced by the FREEWAY Sector to Runway 8. I heard the FREEWAY Controller say the Airbus had my B737 in sight and was instructed to maintain visual separation. My B737 corrected and reestablished themself on the Runway 7R localizer and continued and completed their approach for Runway 7R. The Airbus did so as well. According to the 7110.65; I was 'okay' in this incident because I cleared my aircraft for a visual approach to Runway 7R before separation was lost due to the fact that the Runways 8 and 7R are more than 4300 FT apart. Aircraft came approximately 1 to 2 miles apart; but this was an unsafe situation due to my B737 overshooting the localizer. In retrospect; I should have turned the B737 to intercept and join the visual approach to Runway 7R just a little bit sooner. I waited longer because I was trying to provide wake turbulence separation. The B737 did report the Heavy KC35 in sight and was instructed to 'follow......caution wake turbulence'. Because of this incident; there was a 'snowball' effect; and two or three subsequent arrivals collapsed in regards to spacing. For the next two or three arrivals I had marginal separation and had to call the tower to request visual separation. The tower approved all requests for visual separation and stated that aircraft were 'in sight'. Recommendation; I would recommend that we stop being encouraged to 'SWAP' runways so much. I felt compelled to give my runway away during this scenario for the Heavy KC35 being worked by FREEWAY. If I did not give my runway away during this scenario; it would have not happened the way it did. It was a complex scenario because the KC35 had to cross the Runway 8 final and 'hit a hole' in front of several of my straight in arrivals as well as a downwind aircraft. It helps if the other Final Controller realizes when requesting a 'swap' is going to cause undue hardship to the other final.

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.