Narrative:

I was working final west with 3 planes. We just swapped runways from runway 7L to runway 7R for snow removal. I created a workable hole to put air carrier X behind air carrier Y and ahead of another heavy. I issued speed control after vectoring the B737 behind the first heavy on final. For the entire time on the final; I had separation until compression indicated I would lose 5 mi behind the heavy on final so I broke the B737 out prior to losing 5 mi. At the point on final I'm accused of losing separation; I had in excess of 4 mi when I needed 3. When the B737 was established on final behind the heavy; he was more than 5 mi in-trail and 30 KTS slower. I got this spacing by slowing the aircraft to ensure it would hold. Later; the heavy slowed so much; I had to break the B737 out. I contend there was no loss of separation on final. To my surprise; anchorage tower called the operations manager to launch an investigation of the spacing between these 2 aircraft and after reviewing the playback of the event; local management determined that I had less than 5 mi behind the heavy but he was not yet established on final; so I only needed 3. Since he was slower; when the B737 joined final; he was 5 mi plus behind so all along I believed I had standard separation. Later; when it was apparent the lead aircraft slowed too much and I would lose separation; I canceled the B737 approach clearance; broke him out and re-sequenced him. I tried to make it work and it didn't but I never believed I lost separation.

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Original NASA ASRS Text

Title: A11 CONTROLLER EXPERIENCED OPERATIONAL ERROR WHEN B737 LOST SEPARATION FROM PRECEDING HEAVY AIRCRAFT ON FINAL; CORRECTIVE VECTOR ACTION WAS TOO LATE.

Narrative: I WAS WORKING FINAL W WITH 3 PLANES. WE JUST SWAPPED RWYS FROM RWY 7L TO RWY 7R FOR SNOW REMOVAL. I CREATED A WORKABLE HOLE TO PUT ACR X BEHIND ACR Y AND AHEAD OF ANOTHER HVY. I ISSUED SPD CTL AFTER VECTORING THE B737 BEHIND THE FIRST HVY ON FINAL. FOR THE ENTIRE TIME ON THE FINAL; I HAD SEPARATION UNTIL COMPRESSION INDICATED I WOULD LOSE 5 MI BEHIND THE HVY ON FINAL SO I BROKE THE B737 OUT PRIOR TO LOSING 5 MI. AT THE POINT ON FINAL I'M ACCUSED OF LOSING SEPARATION; I HAD IN EXCESS OF 4 MI WHEN I NEEDED 3. WHEN THE B737 WAS ESTABLISHED ON FINAL BEHIND THE HVY; HE WAS MORE THAN 5 MI IN-TRAIL AND 30 KTS SLOWER. I GOT THIS SPACING BY SLOWING THE ACFT TO ENSURE IT WOULD HOLD. LATER; THE HVY SLOWED SO MUCH; I HAD TO BREAK THE B737 OUT. I CONTEND THERE WAS NO LOSS OF SEPARATION ON FINAL. TO MY SURPRISE; ANCHORAGE TWR CALLED THE OPS MGR TO LAUNCH AN INVESTIGATION OF THE SPACING BTWN THESE 2 ACFT AND AFTER REVIEWING THE PLAYBACK OF THE EVENT; LCL MGMNT DETERMINED THAT I HAD LESS THAN 5 MI BEHIND THE HVY BUT HE WAS NOT YET ESTABLISHED ON FINAL; SO I ONLY NEEDED 3. SINCE HE WAS SLOWER; WHEN THE B737 JOINED FINAL; HE WAS 5 MI PLUS BEHIND SO ALL ALONG I BELIEVED I HAD STANDARD SEPARATION. LATER; WHEN IT WAS APPARENT THE LEAD ACFT SLOWED TOO MUCH AND I WOULD LOSE SEPARATION; I CANCELED THE B737 APCH CLRNC; BROKE HIM OUT AND RE-SEQUENCED HIM. I TRIED TO MAKE IT WORK AND IT DIDN'T BUT I NEVER BELIEVED I LOST SEPARATION.

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