Narrative:

It was low IFR conditions with snow and 1/2 mile tower visibility. I cleared aircraft X off of runway 34L via RNAV to brkem; the transition fix to the south. This procedure requires a left turn to the southwest. I then used a staggered departure time for aircraft Y off of 34R to the east. When aircraft X was clearly in his turn to the southwest; I cleared the next south gate departure off of runway 34L. When aircraft Y tagged up I was scanning my strips and the airport surface detection equipment (asde-X). When I looked at the stars display I was surprised and alarmed to see aircraft Y target turning west and closing fast on aircraft X. I stopped aircraft Y 's climb at 070; as aircraft X was climbing out of 072. I issued a traffic alert and assigned aircraft Y present heading. The targets merged showing only 300 feet separation about 4 miles west of the field.my controller in charge (controller in charge) was monitoring the frequency and told me it was a false target for aircraft Y who was really flying runway heading off of 34R. I then told aircraft Y traffic no factor and cleared him back on course with a continued climb.I thought I was witnessing a near midair collision. This was the scariest thing I have seen in my years. Nothing else is even close.please work on the radar/fusion to mitigate these occurrences. But also; if you can share the replay so that a target jump is more readily recognized.the false target does not show up on falcon.

Google
 

Original NASA ASRS Text

Title: Denver Center Traffic Management Coordinator reported of a false target that looked like a Near Mid Air Collision. Controller stated it was the scariest thing he had seen and wanted someone to work on the RADAR/FUSION problem.

Narrative: It was low IFR conditions with snow and 1/2 mile tower VIS. I cleared Aircraft X off of Runway 34L via RNAV to BRKEM; the transition fix to the south. This procedure requires a left turn to the southwest. I then used a staggered departure time for Aircraft Y off of 34R to the east. When Aircraft X was clearly in his turn to the southwest; I cleared the next south gate departure off of Runway 34L. When Aircraft Y tagged up I was scanning my strips and the Airport Surface Detection Equipment (ASDE-X). When I looked at the STARS display I was surprised and alarmed to see Aircraft Y target turning west and closing fast on Aircraft X. I stopped Aircraft Y 's climb at 070; as Aircraft X was climbing out of 072. I issued a Traffic Alert and assigned Aircraft Y present heading. The targets merged showing only 300 feet separation about 4 miles west of the field.My Controller in Charge (CIC) was monitoring the frequency and told me it was a false target for Aircraft Y who was really flying Runway heading off of 34R. I then told Aircraft Y traffic no factor and cleared him back on course with a continued climb.I thought I was witnessing a NMAC. This was the scariest thing I have seen in my years. Nothing else is even close.Please work on the Radar/Fusion to mitigate these occurrences. But also; if you can share the replay so that a target jump is more readily recognized.The false target does not show up on FALCON.

Data retrieved from NASA's ASRS site 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.