NAV ERROR ADMITTED IN HDG TRACK POS DEV.

Narrative

WE HAD FLOWN W ON A NAT TRACK (N ATLANTIC TRACK) WITH AN INLAND FIX AT LAKES INTXN. THE CAPT HAD ENTERED OUR RTE PRIOR TO TKOF AND I CHKED IT BY GOING DOWN OUR FLT PLANNING FORM AND ENTERING THE WINDS ALOFT AT THE FLT PLAN FIXES. THE CAPT HAD ENTERED THE RTE AS LAKES DIRECT MOFAT; OUR FILED AND SUBSEQUENTLY CLRED RTE WAS LAKES NA 316 MOFAT. THESE 2 RTES WERE NOT THE SAME -- THE CLRED RTE WENT LAKES-HINGE-TEALS-MOFAT. MY CHKING THE RTE WITH THE FLT PLAN FORM DID NOT CATCH THE ERROR SINCE HINGE AND TEALS WERE NOT ON THE FORM. OUR FLT WAS AN ETOPS FLT; WITH A RELIEF PLT. JUST AFTER CTR ISSUED OUR CLRNC; I WAS RELIEVED AND WENT ONTO A REST PERIOD IN THE CABIN. NORMALLY THIS IS WHERE SOMEBODY WOULD DOUBLECHK THE FMS RTE WITH THE BOOK; BUT WITH THE SHIFT CHANGE AND SOME COMPLACENCY; NONE OF US DID. THE RESULT WAS A NAV DEV THAT CTR DISCOVERED; WITH NO APPARENT COMPROMISE OF SEPARATION. IN THE FUTURE; I WILL CHK OUR FMS LOADED RTE WITH THE FLT PLAN FILED RTE SECTION AND WILL ALSO MAKE A GREATER EFFORT TO GUARD AGAINST COMPLACENCY. A COPY OF THIS (DE-IDENTED; OF COURSE) WILL GO TO OUR TRAINING PEOPLE SO THAT MAYBE OTHERS WILL NOT BE CAUGHT BY THE METHOD I USED TO CHK OUR RTE.