Narrative:

Aircraft X checked onto my frequency at flight level 340 requesting FL360. As soon as I was able; I climbed him to FL360. At this point he was approximately 40 miles from opposite direction traffic climbing out of dfw. I anticipated separation and climbed aircraft Y to FL350 (I believe he was out of FL310 when this was issued). A few minutes later; I noticed aircraft X was levelling at FL355. Concerned they now might be traffic with aircraft Y; I asked aircraft X to report level at FL360. No response. I attempted again; no response. I then noticed aircraft X descending (FL354) head-on into aircraft Y. Two immediate clearances were issued; one to aircraft X (30 degrees right; no response) and one to aircraft Y (descend to FL330). Shortly after the immediate clearances were issued; aircraft X responded and told us he was trying to get a hold of us and was turning left 30 degrees. I can only assume we kept blocking each other out although I never heard him transmit anything. He went on to tell me that there was a ghost target 400 feet above where he was (FL355). There was no traffic 400 feet above. He leveled off without saying anything and stayed there for several minutes. I queried him on receiving a TCAS RA and he said that he did not receive one. The target for aircraft X was in the vicinity of two others: aircraft Y (now at FL340) and another carrier (directly above at FL390). After getting things somewhat stabilized; aircraft X mentioned over the frequency that this same airplane had similar issues that were previously reported. It's my mistake for anticipating separation; however working a heavy departure sector we have to take some calculated risk getting aircraft safely to altitude. The immediate actions that were taken did not result in a loss of separation and more importantly kept the planes separated. Going forward I will start using a time to climb clearance and focus on calling traffic earlier to key in the pilots on the traffic situation as well. As for the pilot; I understand that he has a duty to keep the passengers safe. Avoiding a ghost target; in my opinion; was the right move on his part. I wish he would have advised us prior to taking action then it would have been a non-event; but as he mentioned he said he made an attempt to tell us with no response. If the plane really did have previous reports of this issue then I believe that needs to be a priority for this airline and the FAA. Had the pilot of aircraft X decided to descend to FL350 or FL345 on his own to avoid the conflict; there very well could have been a midair collision. Thankfully we're just talking about faulty equipment that can be fixed.

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Original NASA ASRS Text

Title: ZFW controller reports of an aircraft that doesn't climb because of a false target being displayed on their TCAS. Controller had climbed aircraft to requested altitude and then became traffic for another aircraft because it didn't climb to requested altitude. Pilot told controller this problem happened with the aircraft before. Event lead to a loss of separation.

Narrative: Aircraft X checked onto my frequency at Flight Level 340 requesting FL360. As soon as I was able; I climbed him to FL360. At this point he was approximately 40 miles from opposite direction traffic climbing out of DFW. I anticipated separation and climbed Aircraft Y to FL350 (I believe he was out of FL310 when this was issued). A few minutes later; I noticed Aircraft X was levelling at FL355. Concerned they now might be traffic with Aircraft Y; I asked Aircraft X to report level at FL360. No response. I attempted again; no response. I then noticed Aircraft X descending (FL354) head-on into Aircraft Y. Two immediate clearances were issued; one to Aircraft X (30 degrees right; no response) and one to Aircraft Y (descend to FL330). Shortly after the immediate clearances were issued; Aircraft X responded and told us he was trying to get a hold of us and was turning left 30 degrees. I can only assume we kept blocking each other out although I never heard him transmit anything. He went on to tell me that there was a ghost target 400 feet above where he was (FL355). There was no traffic 400 feet above. He leveled off without saying anything and stayed there for several minutes. I queried him on receiving a TCAS RA and he said that he did not receive one. The target for Aircraft X was in the vicinity of two others: Aircraft Y (now at FL340) and another carrier (directly above at FL390). After getting things somewhat stabilized; Aircraft X mentioned over the frequency that this same airplane had similar issues that were previously reported. It's my mistake for anticipating separation; however working a heavy departure sector we have to take some calculated risk getting aircraft safely to altitude. The immediate actions that were taken did not result in a loss of separation and more importantly kept the planes separated. Going forward I will start using a time to climb clearance and focus on calling traffic earlier to key in the pilots on the traffic situation as well. As for the pilot; I understand that he has a duty to keep the passengers safe. Avoiding a ghost target; in my opinion; was the right move on his part. I wish he would have advised us prior to taking action then it would have been a non-event; but as he mentioned he said he made an attempt to tell us with no response. If the plane really did have previous reports of this issue then I believe that needs to be a priority for this airline and the FAA. Had the pilot of Aircraft X decided to descend to FL350 or FL345 on his own to avoid the conflict; there very well could have been a midair collision. Thankfully we're just talking about faulty equipment that can be fixed.

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.