Narrative:

I had 4 aircraft that were being vectored to final approach course. 3 were already on final and 1 was just west of localizer. The second one began to overtake the first aircraft, so I slowed him down 10 KTS. I then realized that the speeds were not going to work so I turned the second aircraft off the approach and told him to do a 360 degree turn to reintercept the localizer. By doing this I also had to turn the #3 aircraft. When the #3 aircraft turned I didn't think he would conflict with the fourth aircraft because that aircraft at the time was not on the localizer. However, when the third aircraft was turning back onto the final approach course the fourth aircraft turned onto the localizer and there was a loss of sep. I believe this error was caused by 2 factors: first, sector overload. I was working a total of 6 aircraft in the pattern at 1 airport and also another aircraft at another airport in the sector. Also I had another situation developing that had to be corrected. Second, controller oversight. I thought the fourth aircraft was going to go through the localizer, but he ended up intercepting it which caused the loss of sep. Callback conversation with reporter revealed the following: controller assigned to ZSE and working a low altitude sector which encompasses pae. The incident occurred approximately 18 mi north of pae on final approach. Radar sep required in the pae area is 3 mi due to antenna location. The WX was VFR. Aircraft involved were small aircraft making practice approachs. C/a activated and the controller initiated vectors to re-establish sep. The controller was working the sector decombined with moderate traffic complexity.

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Original NASA ASRS Text

Title: CTLR LOST SEPARATION WITH ACFT WHILE ATTEMPTING TO SEQUENCE TRAFFIC ON FINAL APCH. OPERATIONAL ERROR.

Narrative: I HAD 4 ACFT THAT WERE BEING VECTORED TO FINAL APCH COURSE. 3 WERE ALREADY ON FINAL AND 1 WAS JUST W OF LOC. THE SECOND ONE BEGAN TO OVERTAKE THE FIRST ACFT, SO I SLOWED HIM DOWN 10 KTS. I THEN REALIZED THAT THE SPDS WERE NOT GOING TO WORK SO I TURNED THE SECOND ACFT OFF THE APCH AND TOLD HIM TO DO A 360 DEG TURN TO REINTERCEPT THE LOC. BY DOING THIS I ALSO HAD TO TURN THE #3 ACFT. WHEN THE #3 ACFT TURNED I DIDN'T THINK HE WOULD CONFLICT WITH THE FOURTH ACFT BECAUSE THAT ACFT AT THE TIME WAS NOT ON THE LOC. HOWEVER, WHEN THE THIRD ACFT WAS TURNING BACK ONTO THE FINAL APCH COURSE THE FOURTH ACFT TURNED ONTO THE LOC AND THERE WAS A LOSS OF SEP. I BELIEVE THIS ERROR WAS CAUSED BY 2 FACTORS: FIRST, SECTOR OVERLOAD. I WAS WORKING A TOTAL OF 6 ACFT IN THE PATTERN AT 1 ARPT AND ALSO ANOTHER ACFT AT ANOTHER ARPT IN THE SECTOR. ALSO I HAD ANOTHER SITUATION DEVELOPING THAT HAD TO BE CORRECTED. SECOND, CTLR OVERSIGHT. I THOUGHT THE FOURTH ACFT WAS GOING TO GO THROUGH THE LOC, BUT HE ENDED UP INTERCEPTING IT WHICH CAUSED THE LOSS OF SEP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: CTLR ASSIGNED TO ZSE AND WORKING A LOW ALT SECTOR WHICH ENCOMPASSES PAE. THE INCIDENT OCCURRED APPROX 18 MI N OF PAE ON FINAL APCH. RADAR SEP REQUIRED IN THE PAE AREA IS 3 MI DUE TO ANTENNA LOCATION. THE WX WAS VFR. ACFT INVOLVED WERE SMA MAKING PRACTICE APCHS. C/A ACTIVATED AND THE CTLR INITIATED VECTORS TO RE-ESTABLISH SEP. THE CTLR WAS WORKING THE SECTOR DECOMBINED WITH MODERATE TFC COMPLEXITY.

Data retrieved from NASA's ASRS site as of August 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.