CAPT OF A DC10 MISPROGRAMMED THE FMS RESULTING IN GETTING OFF OF AN OCEANIC AIRWAY FOR A SHORT TIME UNTIL HE FOUND THE MISTAKE AND TURNED BACK ON TRACK.

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MY COMPANY RECENTLY CREATED A SERIES OF NON AUGMENTED 12- DAY EUROPEAN TRIPS THAT INCLUDED 8 ATLANTIC XINGS AND ONLY 7 DESIGNATED LAYOVERS. I BELIEVE THAT CHRONIC FATIGUE; DEVELOPED ON THIS TRIP; CONTRIBUTED TO WHAT COULD HAVE BECOME A POTENTIAL NAV ERROR. THE PROB OCCURRED WHEN I APPARENTLY MISENTERED A NAV COORDINATE DURING PREFLT. DESPITE FOLLOWING ALL PROCS; I MUST HAVE CREATED THE ERROR AND MISSED THE ERROR DURING ONE OF THE SEVERAL TIMES WHEN I WAS INTERRUPTED DURING THE INITIAL LOADING AND SUBSEQUENT CHKING OF THE COORDINATES. THE OTHER 2 CREW MEMBERS ALSO MISSED THE ERROR IN THEIR CHKS. FOR ABOUT 40 MINS PRIOR TO THE FIX FROM WHICH THE ERROR WAS DISCOVERED; MUCH OF MY TIME WAS DIVIDED BTWN TURB RPTS; ATC RPTS; NAV CHKS AND CLRNCS; PA'S AND COORD WITH STAFF FOR SECURING SVC. MOMENTS BEFORE XING THE NEXT FIX; TURB AND MACH EXCURSIONS BECAME QUITE PRONOUNCED AND MY ATTN WAS DRAWN TO THE FO'S HANDLING OF THE SPD VARIATIONS. I LET THIS INTERRUPT OUR NORMALLY WELL DISCIPLINED PROCS OF EACH CREW MEMBER CHKING THE NEXT FIX FOR VERIFICATION WITH THE FLT PLAN AND THEN VERIFYING THE SWITCH TO THE NEXT LEG. INSTEAD; THE FIX CAME AND THE SWITCH OCCURRED BEFORE I COULD VERIFY THE COORDINATES. HOWEVER; WE DID SEE THE CHANGE TO THE NEXT LEG OCCUR AND I PROCEEDED TO MAKE THE ATC RPT AND PREPARED FOR AN ACCURACY CHK. I THEN DISCOVERED THAT THE FIX WE WERE GOING TO WAS NOT CORRECT. WE RE-ENTERED THE CORRECT 'TO' COORDINATES AND WITHIN A FEW MINS RETURNED TO THE CTRLINE OF OUR TRACK. WITH ALL THE REDUNDANCY IN OUR NAV PROCS THIS WAS THE LAST CHANCE TO CATCH THE ERROR. FORTUNATELY IT WORKED. UNFORTUNATELY IT HAD TO BE USED! CONTRIBUTING FACTORS: THIS WAS THE 10TH DAY OF OUR 12 DAY EVENT AND I BELIEVE THAT CHRONIC FATIGUE BROUGHT ON BY THE DESIGN OF THE TRIP WAS A MAJOR PART OF THIS PROB. ADDITIONALLY THOUGH; THE SHEER VOLUME OF MECHANICAL AND DISPATCH PROBS; INCLUDING RESCHEDULING AND CONTRACTUAL DUTY TIME MAX'S; WORE US DOWN EVEN FURTHER. THIS LEFT ME WITH LITTLE RESERVE FOR COPING WITH ADDITIONAL PROBS. ALSO; BY THE TIME I ARRIVED AT OUR DEST; I HAD BEGUN TO FEEL QUITE ILL AND SUBSEQUENTLY SPENT THE NEXT 30 HRS IN BED. HOWEVER; BY THE TIME PICKUP CAME THE NEXT DAY I FELT FINE. IT MAY HAVE BEEN EITHER FOOD OR A MILD FLU. IN MY 20 YRS AS AN AIRLINE PLT; I HAVE NEVER SEEN MURPHY WORK HIS WILY WAYS TO SUCH EXCESS. WE SIMPLY MUST HAVE FAA MANDATED CREW AND DUTY TIME LIMITS THAT RECOGNIZE CIRCADIAN DISRUPTION AND ITS INFLUENCE ON MULTIPLE OCEAN XINGS AND CREW PERFORMANCE. PLT ASSOCIATIONS OFTEN CANNOT REACT QUICK ENOUGH TO PREVENT SUCH SCHEDULING AND THE KIND OF FATIGUE EXPERIENCED IS SUBTLE ENOUGH THAT MANY OF US DON'T RECOGNIZE IT UNTIL IT IS TOO LATE. PLT'S NATURAL DESIRE IS TO COMPLETE THE MISSION. I WILL BE FAR MORE ATTENTIVE TO THE SUBTLE SIGNS IN THE FUTURE AND NOT ALLOW DISTRS TO BREAK THE DISCIPLINE.