GV GULFSTREAM FLT CREW HAS TRACK HDG DEV DURING DEP FROM DAL ON THE DALL8.TTT SID.

Narrative

ATC CLRNC: DALL.8 SID; SWB TRANSITION AS FILED. WE WERE GIVEN SEVERAL ALT AND AIRSPD ASSIGNMENTS WHILE MAINTAINING RWY HDG. WHEN WE WERE CLRED TO THE FIRST FIX ON THE SID (CLARE) THE FIX WAS IN OUR 9-10 O'CLOCK POS APPROX 20 MI. WE WERE AT 250 KIAS ASSIGNED. THE AUTOPLT; LNAV; MANUAL AIRSPD WERE ENGAGED. THE FMS WAS SLOW IN ACQUIRING CLARE AND EVENTUALLY STEERED THE ACFT TOWARDS THE FIX. WHEN THE ACFT FINALLY ESTABLISHED ON COURSE; CLARE WAS BEHIND US AND POTEN; TEKBE AND SWB WERE IN FRONT OF US. WE WERE GIVEN ADDITIONAL ALT AND AIRSPD CHANGES. ATC WAS VERY BUSY WITH MANY TARGETS ON THE TCAS. THE RADIO WAS CLUTTERED WITH MANY XMISSIONS BEING STEPPED ON. DURING THIS TIME WE NOTICED THAT THERE WAS AN ERROR IN OUR ETE AND MILEAGE TO DEST. I CONFIRMED THAT WE WERE ON COURSE WITH OUR FIXES IN FRONT OF US AND ASKED THAT WE WAIT UNTIL TOC TO WORK OUT THE DISCREPANCY. I CONTINUED TO MONITOR THE TFC AND THE FLT GUIDANCE PANEL. ATC ASKED US IF WE WERE PROCEEDING TOWARDS TEKBE AND WHEN I CHKED MY FMS TEKBE WAS NO LONGER THERE AND SWB WAS IN FRONT OF US. ATC ASKED US TO TURN 20 DEGS L; WE DID AND ASKED ATC IF WE SHOULD MAINTAIN THE HDG AND WE WERE TOLD TO DIRECT TEKBE. TEKBE WAS RE-ENTERED IN THE FMS AND WE PROCEEDED ON COURSE.