FLC OF ACR WDB ACFT INADVERTENTLY PROGRAMMED THE ACFT NAV COMPUTER IN ERROR RESULTING IN A 'GROSS' NAV ERROR DURING OP IN OCEANIC AIRSPACE.

Narrative

WE WERE OPERATING A TRIP FROM LAGOS NIGERIA TO JFK WITH A TECH STOP IN SANTA MARIA AZONES. AS WE LEFT THE MINNEAPOLIS AIRSPACE AT N45/50W DIRECT BANCS INTXN. WE CONTACTED GANDER CTR. THEY CHANGED OUR ROUTING AFTER BANCS INTXN TO NORTH AMERICAN RTE 22 (BANCS DIRECT KANNI INTXN PART OF THE PLYMOUTH 3 ARR INTO JFK). WE ENTERED THE COORDINATES FOR KANNI INTO WAYPOINT POS #2. THE CAPT THEN INSERTED INTO THE INS TRACK CHANGE #7 TO #2. #7 WAS THE WAYPOINT BEHIND US #8 WAS BANCS. THE ACFT THEN TURNED TO A SOUTHERLY HDG TO INTERCEPT THE WAYPOINT BEHIND US. WE REALIZED THE HDG WAS IN ERROR AND WENT TO HDG MODE AND TURNED BACK TO BANCS INTXN. GANDER CTR CALLED RADAR CONTACT 20 MI S OF BANCS; STILL IN GANDER DOMESTIC AIRSPACE. WE SHOULD HAVE BEEN OVER BANCS AT THAT TIME. HE THEN CLRED US DIRECT KANNI. WE ALL FELT THAT FATIGUE PLAYED A MAJOR PART IN THE ERROR. THE PREVIOUS DAY WE OPERATED JFK-SMA-LOS 10:38 BLOCK HRS. 12 HR CREW REST AT A HOTEL THEN THE RETURN TRIP WHICH ENDED UP TO BE 11:37 BLOCK. I WAS CALLED IN TO OPERATE THE TRIP ON A DAY OFF; SO I WAS UP 24 HRS BEFORE REACHING THE HOTEL. I ALSO BELIEVED ONCE WE DEPARTED THE MINNEAPOLIS AIRSPACE WE BECAME MORE COMPLACENT. WE DIDN'T CHK THE WAYPOINTS AS CONSCIENTIOUSLY AS WE WERE DOING IN THE MINNEAPOLIS AIRSPACE AND THROUGH AFRICA. ANOTHER FACTOR IS THE OTHER ACFT IN THE FLEET HOME FMS'S. THE DISPLAY WHERE WE WERE AND WHERE WE WERE GOING WOULD HAVE BEEN MORE EVIDENT.