Narrative:

In preparation for flight across atlantic (wbound), the INS's were loaded and crosschecked against the flight plan as per company policy. After departure, our north atlantic track was changed and we reloaded the new track in each INS separately, after loading in each track position by 'name,' ie: 5640N, we continued on our way. I did not check that the corresponding coordinates for each fix were correct. The coordinates are preloaded. After crossing a fix position, 57n40w, the aircraft turned to its next, but incorrect fix position. Instead of my INS -- INS #2 -- driving the aircraft to 56n5ow which was the preloaded library fix which we wanted to go to and which was named as next waypoint, it drove us towards 5on56w, the coordinates which were actually loaded under 565ON. The captain's, or #1 INS, was loaded correctly, so when he checked heading, distance and ETA to next point, it all checked ok. The #2 INS, as the one driving the aircraft, was displaying coordinates. We proceeded along wrong course until the captain accomplished the post fix check and noted that we were off intended course on plotting chart. We were approximately 40 mi south of intended course before correcting back. Further examination showed that only #2 INS had incorrect position loaded. This incident could have been precluded if I had checked the coordinates of each new position that was loaded instead of assuming its correctness.

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Original NASA ASRS Text

Title: GROSS NAV ERROR ON THE NAT.

Narrative: IN PREPARATION FOR FLT ACROSS ATLANTIC (WBOUND), THE INS'S WERE LOADED AND XCHKED AGAINST THE FLT PLAN AS PER COMPANY POLICY. AFTER DEP, OUR N ATLANTIC TRACK WAS CHANGED AND WE RELOADED THE NEW TRACK IN EACH INS SEPARATELY, AFTER LOADING IN EACH TRACK POS BY 'NAME,' IE: 5640N, WE CONTINUED ON OUR WAY. I DID NOT CHK THAT THE CORRESPONDING COORDINATES FOR EACH FIX WERE CORRECT. THE COORDINATES ARE PRELOADED. AFTER XING A FIX POS, 57N40W, THE ACFT TURNED TO ITS NEXT, BUT INCORRECT FIX POS. INSTEAD OF MY INS -- INS #2 -- DRIVING THE ACFT TO 56N5OW WHICH WAS THE PRELOADED LIBRARY FIX WHICH WE WANTED TO GO TO AND WHICH WAS NAMED AS NEXT WAYPOINT, IT DROVE US TOWARDS 5ON56W, THE COORDINATES WHICH WERE ACTUALLY LOADED UNDER 565ON. THE CAPT'S, OR #1 INS, WAS LOADED CORRECTLY, SO WHEN HE CHKED HDG, DISTANCE AND ETA TO NEXT POINT, IT ALL CHKED OK. THE #2 INS, AS THE ONE DRIVING THE ACFT, WAS DISPLAYING COORDINATES. WE PROCEEDED ALONG WRONG COURSE UNTIL THE CAPT ACCOMPLISHED THE POST FIX CHK AND NOTED THAT WE WERE OFF INTENDED COURSE ON PLOTTING CHART. WE WERE APPROX 40 MI S OF INTENDED COURSE BEFORE CORRECTING BACK. FURTHER EXAMINATION SHOWED THAT ONLY #2 INS HAD INCORRECT POS LOADED. THIS INCIDENT COULD HAVE BEEN PRECLUDED IF I HAD CHKED THE COORDINATES OF EACH NEW POS THAT WAS LOADED INSTEAD OF ASSUMING ITS CORRECTNESS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.