Narrative:

I was working the sector alone, light traffic, no chop or WX. I watched the 2 aircraft involved for 6-8 mins, monitoring their speeds, and separation. The B747 was nwbound, about 20 KTS faster, and in front. At 8 min, 4 mins, and 2 mins, it looked to me like I would have 6-8 mi separation. Conflict alert activated at about 3 mins, but it still appeared I had 6-7 mi. I had a halo on the B747 and I issued traffic to both aircraft. At about the 2 min point another aircraft, sbound, at FL290 came into close proximity and I believe the radar became confused. The speed on the B747 dropped approximately 40 KTS and the speed on the B757 increased approximately 40 KTS, and the back target jumped into the halo. It printed at 4.85. The sar tape at our facility (ZAB) was not working. We had no internal data to run a satori or ntap, however the aircraft had been handed off to ZDV, so our facility used their data to process the error. I believe what caused the error was erroneous radar data caused by overlapping sort boxes, the close proximity of 3 aircraft which caused speed fluctuations, and the difference in ZDV's data and our facility's data which was not available. I asked our qa office to do some research on the difference of ZDV's data and ours, but to my knowledge, it hasn't been done. If we don't do more about target jumps and speed fluctuations, more errors will occur.

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Original NASA ASRS Text

Title: ZAB CTLR EXPERIENCED LOSS OF SEPARATION WITH ENRTE ACFT AT FL390.

Narrative: I WAS WORKING THE SECTOR ALONE, LIGHT TFC, NO CHOP OR WX. I WATCHED THE 2 ACFT INVOLVED FOR 6-8 MINS, MONITORING THEIR SPDS, AND SEPARATION. THE B747 WAS NWBOUND, ABOUT 20 KTS FASTER, AND IN FRONT. AT 8 MIN, 4 MINS, AND 2 MINS, IT LOOKED TO ME LIKE I WOULD HAVE 6-8 MI SEPARATION. CONFLICT ALERT ACTIVATED AT ABOUT 3 MINS, BUT IT STILL APPEARED I HAD 6-7 MI. I HAD A HALO ON THE B747 AND I ISSUED TFC TO BOTH ACFT. AT ABOUT THE 2 MIN POINT ANOTHER ACFT, SBOUND, AT FL290 CAME INTO CLOSE PROX AND I BELIEVE THE RADAR BECAME CONFUSED. THE SPD ON THE B747 DROPPED APPROX 40 KTS AND THE SPD ON THE B757 INCREASED APPROX 40 KTS, AND THE BACK TARGET JUMPED INTO THE HALO. IT PRINTED AT 4.85. THE SAR TAPE AT OUR FACILITY (ZAB) WAS NOT WORKING. WE HAD NO INTERNAL DATA TO RUN A SATORI OR NTAP, HOWEVER THE ACFT HAD BEEN HANDED OFF TO ZDV, SO OUR FACILITY USED THEIR DATA TO PROCESS THE ERROR. I BELIEVE WHAT CAUSED THE ERROR WAS ERRONEOUS RADAR DATA CAUSED BY OVERLAPPING SORT BOXES, THE CLOSE PROX OF 3 ACFT WHICH CAUSED SPD FLUCTUATIONS, AND THE DIFFERENCE IN ZDV'S DATA AND OUR FACILITY'S DATA WHICH WAS NOT AVAILABLE. I ASKED OUR QA OFFICE TO DO SOME RESEARCH ON THE DIFFERENCE OF ZDV'S DATA AND OURS, BUT TO MY KNOWLEDGE, IT HASN'T BEEN DONE. IF WE DON'T DO MORE ABOUT TARGET JUMPS AND SPD FLUCTUATIONS, MORE ERRORS WILL OCCUR.

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