AN MD80 CREW ON THE DFW TRISS2/TXK WAS FLYING DIRECT TXK AFTER TRISS BECAUSE THE INTERVENING WAYPOINTS DROPPED FROM THE FMS. ATC REDIRECTED ON RTE.

Narrative

WAS NOTIFIED ENRTE TO CONTACT ZFW DUE TO POSSIBLE PLT DEV. CALLED; WAS TOLD WE WERE 6 NM OFF COURSE ON DEP. AUTOPLT WAS ENGAGED FROM INITIAL CLBOUT AND REMAINED ON. WAYPOINTS WERE CHKED AND I DON'T REMEMBER ANYTHING AMISS. THIS WHOLE THING HAS COME AS A SURPRISE SINCE NEITHER OF US ARE AWARE OF WHAT WENT WRONG. IF WE WERE OFF COURSE I WOULD HAVE LIKED TO HAVE KNOWN ABOUT IT AT THE TIME SO MAYBE WE COULD HAVE FIGURED OUT WHAT HAPPENED. THIS EVENT HAS REALLY BOTHERED ME SINCE I HONESTLY CANNOT RECONSTRUCT WHAT WENT WRONG AND I WISH I COULD BECAUSE IF I SCREWED UP; I DON'T WANT TO DO IT AGAIN. WE WERE NOT NOTIFIED THAT ANYTHING WAS WRONG UNTIL WE WERE SEVERAL HUNDRED MILES DOWN TRACK AND BY THEN EVERYTHING WAS GONE AS FAR AS OUR FMS AND BOTH MINE AND MY FO'S MEMORIES. I HAVE BEEN LOOKING AROUND ON THE WEBSITE AND FOUND ALERT BULLETIN 2006:6/8-1 AND THAT SOUNDS AS THOUGH THAT MIGHT HAVE BEEN WHAT HAPPENED TO US. I GUESS WE MISSED SHERO; ALL I KNOW IS THAT WE WERE TOLD WE WERE 6 NM OFF COURSE AND THAT CAME FROM MY PHONE CALL TO CTR ON ARR AT ZZZ. I CANNOT REMEMBER IF WE WERE CLRED DIRECT PRIOR TO SHERO AND IT DROPPED OR IF THE FMS ERROR OCCURRED EARLIER THAN THAT. TOO MUCH TIME HAS GONE BY. I DO CHK THE WAYPOINTS AS PROC; I DON'T REMEMBER ANYTHING AMISS. I DO REMEMBER THE CTLR ASKING WHERE WE WERE GOING AND AS I RECALL THAT WAS IN THE MIDDLE OF A REQUEST FOR A HIGHER THAN FILED ALT. I THOUGHT HIS REQUEST FOR OUR NEXT WAYPOINT WAS IN REGARD TO THAT ALT REQUEST AS PART OF HIS COORDINATION. IT IS NOT UNCOMMON FOR THINGS LIKE THAT TO HAPPEN. I HAVE EVEN HAD TO ASK CTLRS IF THEY HAD ME LNDG AT THE SAME ARPT AS ME; THE COMPANY; AND ALL THE PAX WANTED TO LAND AT. SO I DIDN'T TAKE HIS QUERY ABOUT MY NEXT WAYPOINT AS BEING TOO UNUSUAL. I CERTAINLY WASN'T THINKING ABOUT A TRACK DEV SINCE WE WERE COUPLED IN NAV WITH AUTOPLT ON AND ON THE LINE. MY GUESS IS THAT SHERO WAS NOT THERE AND WHERE IT WENT; I DON'T KNOW. MY FO SAYS HE REMEMBERS SEEING IT. I GUESS THAT THE FIRST TURNS AND RESTRICTIONS HAVE BEEN SUCH A PROBLEM THAT ONCE YOU GET BY THOSE YOU KIND OF BREATHE A SIGH OF RELIEF. I KNOW THIS ISN'T MUCH INFO BUT IT IS AS I REMEMBER IT. IF THE AIRPLANE WENT OFF COURSE AS A RESULT OF THE WAY WE OPERATED THE FMS; THEN IT IS OBVIOUSLY MY FAULT; MAYBE IT WAS A 'GOTCHA'. IT WOULD BE NICE IF ZFW NOTICES US DRIFTING OFF COURSE THAT THEY SAY SOMETHING AT THE TIME; IT MAY HAVE HELPED ME FIGURE OUT WHAT WENT WRONG.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE FIRST THE CREW KNEW OF AN ERROR WAS WHEN ATC ASKED; 'WHERE ARE YOU GOING?' THE RPTR'S FIRST RESPONSE WAS HIS DEST; ZZZ. ATC THEN ASKED FOR THE NEXT RTE FIX; TO WHICH THE RPTR STATED TXK. ATC THEN CLRED THEM DIRECT TXK AND RPTR DID NOT KNOW ANYTHING WAS WRONG UNTIL IN CONTACT WITH ABC CTR NEARLY 2 HOURS LATER WHEN THEY WERE GIVEN A PHONE NUMBER TO CALL. THEY WERE INFORMED THAT A DEV WAS BEING FILED ON THEIR 6 NM DEV. AT THAT POINT; THE RPTR HAD NO IDEA WHAT HAD OCCURRED. THIS IS THE FIRST TIME HE HAS EXPERIENCED THIS ERROR AND IT IS HIS BELIEF THAT THE FMS CONTAINS A PROGRAMMING ERROR. HE HAS SEEN THE FMS TURN TO POINTS NOT ON THE FLT PLAN FOR UNKNOWN REASONS. IT WAS THE RPTR'S BELIEF THAT IN THIS DFW DEP ISSUE; WHEN THE FLT WAS CLRED NAVYE DIRECT TRISS; THAT THE WAYPOINT BETWEEN TRISS AND TXK DROPPED OUT WITHOUT CREATING A RTE DISCONTINUITY.