Medium Large Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 30.4
Distraction; Confusion; Troubleshooting
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance
ATC Equipment / Nav Facility / Buildings; Aircraft; Human Factors
Aircraft X was a test flight requesting FL430. Aircraft Y was a JAX departure filed ..ATL.VOLLS8.BNA at FL340. Aircraft X was climbed to FL320; then when Aircraft X was 7 [miles] west of Aircraft Y and still heading to MCN he was climbed to FL340 and handed off to Clark Hill (23).  As Aircraft X was approaching FL340 radar target was lost and track went to coast status.  I advised Aircraft X that I lost his transponder.  He acknowledged and said he would switch to another.  Still no target; then I got one or two hits on his transponder and the aircraft was 5-6 miles directly behind Aircraft Y heading towards AHN.  Clarkhill gave me higher and FL430 was issued with an; 'Expedite!'  I believe Aircraft X turned way before MCN towards AHN and this resulted in the aircraft being directly behind Aircraft Y.  I don't know why we lost radar on Aircraft X; but I do believe this lead to an unsafe situation. If radar had been maintained I would have noticed the early turn and would have taken action much sooner.  If aircraft had flown to MCN or close to MCN then this would not even be an issue; but I honestly believe Aircraft X turned to AHN early.  I don't know if the lost transponder was an equipment problem from ZTL or from the Aircraft X transponder.If it is a problem with our equipment; then correcting it would solve this type of problem. If it was a transponder issue then a correctly working transponder would correct this issue.  If it was a pilot turning too soon; then pilot retraining would solve this type of issue.
ZTL Controller reports of an airborne conflict with an aircraft that has an intermittent transponder; or the FAA radar site doesn't pick up this aircraft at times.