Narrative:

Aircraft X on an IFR flight plan at FL330 north of fti VOR direct gck and aircraft Y IFR hpn..saf. Aircraft Y was descending from FL400 to FL340 due to aircraft X being in conflict about 5.0 lateral separation. I gave aircraft Y a 10 degree left turn to avoid aircraft X and to continue the aircraft's descent into saf. The computer showed 5.1 - 5.3 mi lateral separation. When the 2 aircraft were passing side-by-side the beacon target of aircraft X jumped towards aircraft Y about 1/3 - 2/3 of a mi for 2-3 radar updates and then jumped back to the original course track. This 'target jump' caused the conflict alert to activate and it printed with a loss of separation. The computer replay; falcon; showed the target jump was the cause of the separation loss and that had the target jump not taken place there would have been no loss of separation. Aircraft X received a TCAS RA; which seems to happen at ZAB with less than 5.5 mi separation in a climb or descent mode. The radar area in which this event took place is known for speed jumps but not large target jumps.

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Original NASA ASRS Text

Title: ZAB CTLR DESCRIBED CONFLICT EVENT WHEN TARGETS 'JUMPED;' RESULTING IN A TCAS RA AND CONFLICT ALERT. PLAYBACK CONFIRMED NO SEPARATION LOSS.

Narrative: ACFT X ON AN IFR FLT PLAN AT FL330 N OF FTI VOR DIRECT GCK AND ACFT Y IFR HPN..SAF. ACFT Y WAS DSNDING FROM FL400 TO FL340 DUE TO ACFT X BEING IN CONFLICT ABOUT 5.0 LATERAL SEPARATION. I GAVE ACFT Y A 10 DEG L TURN TO AVOID ACFT X AND TO CONTINUE THE ACFT'S DSCNT INTO SAF. THE COMPUTER SHOWED 5.1 - 5.3 MI LATERAL SEPARATION. WHEN THE 2 ACFT WERE PASSING SIDE-BY-SIDE THE BEACON TARGET OF ACFT X JUMPED TOWARDS ACFT Y ABOUT 1/3 - 2/3 OF A MI FOR 2-3 RADAR UPDATES AND THEN JUMPED BACK TO THE ORIGINAL COURSE TRACK. THIS 'TARGET JUMP' CAUSED THE CONFLICT ALERT TO ACTIVATE AND IT PRINTED WITH A LOSS OF SEPARATION. THE COMPUTER REPLAY; FALCON; SHOWED THE TARGET JUMP WAS THE CAUSE OF THE SEPARATION LOSS AND THAT HAD THE TARGET JUMP NOT TAKEN PLACE THERE WOULD HAVE BEEN NO LOSS OF SEPARATION. ACFT X RECEIVED A TCAS RA; WHICH SEEMS TO HAPPEN AT ZAB WITH LESS THAN 5.5 MI SEPARATION IN A CLB OR DSCNT MODE. THE RADAR AREA IN WHICH THIS EVENT TOOK PLACE IS KNOWN FOR SPD JUMPS BUT NOT LARGE TARGET JUMPS.

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.