FLC OF AN WDB ON N ATLANTIC TRACK GOT OFF TRACK DUE TO MISPROGRAMMING THE INS NAVIGATIONAL COMPUTER.

Narrative

FLT WAS FROM ORY-PARIS TO EWR-NEWARK; VIA N ATLANTIC TRACK 'F'. ALL OF THE N COORDINATES FOR TRACK 'F' WERE 49.00 EXCEPT THE ONE JUST PRIOR TO YYT-TORBAY; AND IT WAS 48.00 N 50.00 W. WHEN LOADING THE INS ON THE GND IN PARIS; 49.00 N AND 50.00 W WAS ENTERED AS A WAYPOINT INSTEAD OF 48.00 N AND 50.00 W. THIS ERROR WAS NOT DETECTED DURING XCHK AND READBACK OF COORDINATES PRIOR TO DEP. AT THIS PARTICULAR PHASE OF THE FLT; MY DUTIES AS A FE REQUIRE ME TO DIRECT MY ATTN ON OTHER ITEMS. THEREFORE; OTHER THAN MAKING CERTAIN THAT THE PROPER 'PRESENT POS' IS CORRECT; I AM NOT INVOLVED IN THE LOADING AND XCHKING OF THE FLT PLAN INTO THE INS. FLT WAS FLOWN AS PROGRAMMED; AND PROPERLY PLOTTED ON PLOTTING CHART. ERROR WAS NOT DISCOVERED UNTIL GANDER ATC QUESTIONED OUR POS OF 40.00N AND 50.00W. THIS CREW IS VERY METICULOUS ABOUT PLOTTING WAYPOINTS; AND MID-POINTS BTWN WAYPOINTS. IT IS MY BELIEF THAT HAD THEIR ATTN NOT BEEN DIVERTED BECAUSE OF AN ABNORMALITY IN THE DISPLAY OF INS INFO AT 49.00 N AND 45.00 W; THIS ERROR WOULD HAVE BEEN DETECTED AN CORRECTED WHEN THE PLT WAS ENTERED ON THE CHART. THIS PLOT WAS NOT MADE BECAUSE ATTN WAS FOCUSED ON WHY CERTAIN INFO WAS BEING DISPLAYED ON INS.