B757-200 EXPERIENCES LOSS OF TRANSITION LEGS OF CLARE RNAV SID OUT OF DFW.

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THE FO AND I RAN ALL THE PREFLT CHKS 'BY THE BOOK.' WHEN IT CAME TIME TO REVIEW THE RTE; I READ THE RTE TO HIM FROM THE FMC WHILE HE FOLLOWED ALONG ON THE FLT PLAN. I THEN READ ALL FIXES TO HIM BY STEPPING THROUGH ALL THE WAYPOINTS ON THE LEGS PAGE. FOR THE DEP PORTION OF THE STEP THROUGH HE HAD THE CLARE2 DEP IN HIS HAND AS I READ THE WAYPOINTS (WITH ALT AND AIRSPD RESTRAINTS) TO HIM. FOR THE BALANCE OF THE FLT; ALL WAYPOINTS WERE CHKED AGAINST THE FLT PLAN. THERE WERE NUMEROUS DISTRACTIONS THE WHOLE TIME WE WERE TRYING TO ACCOMPLISH THIS; BUT BOTH OF US FEEL CONFIDENT ALL WAYPOINTS WERE LOADED; AND WERE IN THE PROPER ORDER. ON DEP; SHORTLY AFTER PASSING CLARE INTXN; ZFW ASKED US ABOUT OUR ROUTING. A CHK OF THE FMC SHOWED WE WERE PROCEEDING DIRECT TO SAWMILL (SWB). WE WERE INFORMED WE WERE NOT ON THE PROPER COURSE. IT WAS AT THIS TIME WE REALIZED TWO WAYPOINTS; POTEN AND TEKBE WERE MISSING ON THE LEGS PAGE. SHORTLY THEREAFTER; WE WERE TOLD TO CALL ZFW UPON ARR IN TO DISCUSS THE DEPARTURE FROM OUR CLRNC. FOR THE BALANCE OF THE TRIP; THE FO AND I TRIED TO FIGURE OUT JUST HOW THIS HAPPENED; BUT WERE AT A LOSS FOR AN EXPLANATION. AS REQUESTED; I CALLED ZFW UPON ARR AND TALKED TO THE OPS MANAGER. HE INFORMED ME THAT WE HAD INDEED DEPARTED FROM THE CLRED RTE; BUT ADDED SOME INTERESTING INFO. HE TOLD ME HE HAD PREVIOUSLY SEEN THE VERY SAME SCENARIO (DEPARTURE FROM CLRNC) ENCOUNTERED OVER THE SAME FIXES (CLARE AND SWB) RECENTLY BY ANOTHER CREW. IN THE LIGHT OF THIS; ONE CANNOT HELP BUT THINK THERE COULD BE AN ANOMALY IN THE FMC SOFTWARE CAUSING THIS TO TAKE PLACE. IF THIS IS NOT THE CASE; THEN THE ONLY LOGICAL POSSIBILITY IS CREW ERROR IN CONFIRMING THE RTE PRIOR TO DEP. I FIND THIS DIFFICULT TO BELIEVE; BUT BECAUSE OF ALL THE DISTRACTIONS; REALIZE IT IS A POSSIBILITY.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR; A FORMER CHK AIRPERSON AND SELF DESCRIBED STICKLER FOR SOP; WAS AT A LOSS TO EXPLAIN THE EVENT; THE ONLY TIME RPTR HAS EXPERIENCED THIS NOW FAIRLY COMMON ANOMALY. RPTR DESCRIBED IN DETAIL THE MANNER IN WHICH THE RTE WAS VERIFIED BOTH BY AIRWAYS ON THE FMS RTE PAGE AND WAYPOINT BY WAYPOINT ON THE FMS LEGS PAGE. THE ENRTE PORTION OF THE FLT PLAN WAS DOWNLINKED FROM THE COMPANY COMPUTERS AND THE SID TRANSITION LOADED BY THE COPLT. RPTR WAS 95% CERTAIN THE TRANSITION HAD BEEN LOADED BUT -- SINCE THE VERIFICATION WAS DONE VIA A COMPARISON WITH THE PAPER FLT PLAN; WHICH DOES NOT INCLUDE THE SID/TRANSITION WAYPOINTS -- IT IS CONCEIVABLE THAT THE SID HAD BEEN LOADED AND A DISCONTINUITY BETWEEN CLARE AND SWB CLOSED. HE THOUGHT THIS MIGHT BE POSSIBLE IN LIGHT OF THE MANNER IN WHICH THE PDC PRINTOUT FAILS TO MAKE IT CLR THAT 'SWB' MEANS SWB TRANSITION AND NOT SIMPLY DIRECT SWB AFTER CLARE. RPTR ALSO MENTIONED THAT DUE TO WX; THEY DID NOT FLY THE INITIAL PORTION OF THE SID; BUT WERE VECTORED AROUND THE WX AND EVENTUALLY CLRED DIRECT TO CLARE AND ON COURSE.