Narrative:

Small transport X was climbing southbound from the lunken airport and was assigned a 180 degree heading by me for his climb. I then received a handoff from my high side controller on small transport Y. I called my high side controller and requested a higher altitude on small transport X. The high side approved a climb to FL270 with respect to small transport Y wbound into standiford descending to FL240. The gndspd on small transport X was indicating 350 KTS and small transport Y was also indicating a gndspd of 350 KTS on my radar. I used my vector lines on my radar to determine that the 2 aircraft in question would pass each other with approximately 10 mi. I then turned my attention toward another situation was evolving in my sector. At this time my attention was turned back to small transport X and small transport Y when C/a notification was activated. I immediately told small transport Y to turn 20 degrees to the right to avoid traffic. I had already lost vertical sep on both of these aircraft so latitude sep was my next option to obtain standard sep. The investigation that then followed concluded that the aedp was activated by a target jump east of the course of flight of small transport X. I had never gone below the standard of 5 mi. Using the information provided I made the determination that the gndspd depicted on my radar was not an accurate account of the actual speed across the ground caused by an inconsistent radar tracking of the computer. In reality the southbound aircraft was about 50 KTS slower than what was presented to me on the radar, thus creating an overtake situation with the wbound aircraft. I'm not sure what can be done to the radar system that would prevent such poor tracking on targets.

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Original NASA ASRS Text

Title: ACFT WAS ISSUED VECTORS AVOID AROUND ANOTHER ACFT IN ORDER TO MAINTAIN RADAR SEPARATION.

Narrative: SMT X WAS CLBING SBND FROM THE LUNKEN ARPT AND WAS ASSIGNED A 180 DEG HDG BY ME FOR HIS CLB. I THEN RECEIVED A HDOF FROM MY HIGH SIDE CTLR ON SMT Y. I CALLED MY HIGH SIDE CTLR AND REQUESTED A HIGHER ALT ON SMT X. THE HIGH SIDE APPROVED A CLB TO FL270 WITH RESPECT TO SMT Y WBOUND INTO STANDIFORD DSNDING TO FL240. THE GNDSPD ON SMT X WAS INDICATING 350 KTS AND SMT Y WAS ALSO INDICATING A GNDSPD OF 350 KTS ON MY RADAR. I USED MY VECTOR LINES ON MY RADAR TO DETERMINE THAT THE 2 ACFT IN QUESTION WOULD PASS EACH OTHER WITH APPROX 10 MI. I THEN TURNED MY ATTN TOWARD ANOTHER SITUATION WAS EVOLVING IN MY SECTOR. AT THIS TIME MY ATTN WAS TURNED BACK TO SMT X AND SMT Y WHEN C/A NOTIFICATION WAS ACTIVATED. I IMMEDIATELY TOLD SMT Y TO TURN 20 DEGS TO THE RIGHT TO AVOID TFC. I HAD ALREADY LOST VERT SEP ON BOTH OF THESE ACFT SO LAT SEP WAS MY NEXT OPTION TO OBTAIN STANDARD SEP. THE INVESTIGATION THAT THEN FOLLOWED CONCLUDED THAT THE AEDP WAS ACTIVATED BY A TARGET JUMP E OF THE COURSE OF FLT OF SMT X. I HAD NEVER GONE BELOW THE STANDARD OF 5 MI. USING THE INFO PROVIDED I MADE THE DETERMINATION THAT THE GNDSPD DEPICTED ON MY RADAR WAS NOT AN ACCURATE ACCOUNT OF THE ACTUAL SPD ACROSS THE GND CAUSED BY AN INCONSISTENT RADAR TRACKING OF THE COMPUTER. IN REALITY THE SBND ACFT WAS ABOUT 50 KTS SLOWER THAN WHAT WAS PRESENTED TO ME ON THE RADAR, THUS CREATING AN OVERTAKE SITUATION WITH THE WBOUND ACFT. I'M NOT SURE WHAT CAN BE DONE TO THE RADAR SYS THAT WOULD PREVENT SUCH POOR TRACKING ON TARGETS.

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.