NAV ERROR IN OVERWATER OP.

Narrative

FLT WAS ON R 220 PROCEEDING FROM MUCLA TO MIDLA RPTING POINTS ESTIMATING COMPULSORY RPTING POINT NEVVA AT XY53Z BUT PLANNING BY NON-COMPULSORY RPTING POINT MIDLA AT XY03Z. AT APPROX XI04Z DURING MY SCAN OF THE INSTS THE PRESENT POS INDICATION OF THE #1 INS SHOWED WE WERE SLIGHTLY W OF THE LONGITUDE OF MIDLA AND TRACKING N OF THE AIRWAY. THE INS'S WERE CHKED AND THE LONGITUDE OF MIDLA WAS FOUND TO BE IN ERROR (E INSTEAD OF W DESIGNATION). THE MIDLA LONGITUDE WAS CORRECTED; THE PROPER TRACKLINE WAS ESTABLISHED BTWN MIDLA AND NINNO. IT INDICATED A CROSS-TRACK ERROR OF 28 MI. THE ACFT WAS TURNED IMMEDIATELY TO REGAIN THE AIRWAY AND HNL RADIO WAS INFORMED OF OUR TRACK ERROR; OUR PRESENT POS; AND OUR TURN TO REGAIN THE AIRWAY. WE REPOSITIONED THE ACFT ON THE AIRWAY AND RPTED THIS TO HNL RADIO AT XY12Z AND RE- ESTIMATED NEVVA AT XY56Z. WE OFFERED TO SPD UP TO MAKE OUR ORIGINAL ESTIMATE BUT IT WAS NOT REQUIRED. NO LOSS OF SEPARATION. RADAR OPERATING IN TCASII MODE. NO TARGETS. FAILURE TO FOLLOW PLOTTING PROCEDURE BECAUSE OF DISTRACTION OF RELIEF PLT BRIEFING; PLANNING NEXT ALT CHANGE AND FUEL CHK LED TO FAILURE TO CATCH OFF TRACK MOVEMENT EARLY.