Air Traffic Control Fully Certified
Communication Breakdown; Confusion; Human-Machine Interface; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic
Chart Or Publication; Airspace Structure; Human Factors
Aircraft X departed to their destination via direct. I left him on runway heading until he passed the tower airspace and issued a climb to 5000 feet. I gave him a reroute by routing him via BUBBA. I phonetically spelled BUBBA to the pilot and he read back to go direct 'BUBBA' then direct. I told him to fly heading 130 and direct BUBBA when able. I entered the routing change into the Flight Data Input/Output (FDIO) since I was also working Flight Data. Aircraft Y departed Runway 22 at GSP. I left Aircraft Y on runway heading to pass behind the expected track of Aircraft X with a climb to 100. At this time Aircraft X was already south of the flightpath of Aircraft Y with an expected heading of approximately 120 to BUBBA. I noticed that Aircraft X appeared to be slightly farther north than expected. It appeared he was on a heading of between 060 to 090 degrees. Because I made the entry into the FDIO before Aircraft Y departed; I had only seconds to attempt to determine the unexpected heading of Aircraft X before the aircraft began rapidly converging. I issued Aircraft Y a traffic alert and a turn to heading 270 in an attempt to turn him away from where it appeared Aircraft X was going. I then gave a traffic alert to Aircraft X and he reported the traffic in sight and 'no factor; passing above him'. I told Aircraft X to maintain visual separation with the traffic. Even though approved separation did not exist before applying visual separation I was unsure of where Aircraft X was heading so I wanted to make it clear to him to avoid Aircraft Y. After separation was reestablished I asked the pilot of Aircraft X where he was going. He told me that he was direct to BUBAA instead of BUBBA. The primary cause of this incident is the pilot's failure to navigate to the correct fix. It is possible that the situation could have been less severe if I had a way to more accurately determine the heading of Aircraft X. We are using ARTS IIE radar displays so there are no tools to help determine current heading. It is extremely hard to determine the heading of a slow moving aircraft on our radar equipment. There is little movement between each sweep of the radar and our primary targets actually jump around away from their actual flight path by about half a mile. Due to these factors it is extremely difficult to determine a slow aircraft's current heading in less than 5-6 radar sweeps or approximately 30 seconds. If I had STARS (Radar display and software) with track history or projected tracks enabled I may have been able to more quickly determine the actual track of Aircraft X and give Aircraft Y a more appropriate turn away from Aircraft X by going directly east. Due to the speed in which the situation developed I doubt that any controller would be able to completely avoid a loss of separation; but it's possible that it could have been mitigated.
GSP TRACON Controller reported an aircraft deviated from its assigned course.