A WDB ACR CREW HAD A NAV ERROR WITH THEIR INERTIAL NAV SYS (3) CAUSING A TRACK DEV.

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INS ERROR (TYPE) PUT ACFT 5 MI S OF COURSE AFTER 6 HRS OF FLT FROM HNL TO NGO. WE HAD NO INDICATION OF THE EXTENT OF THE ERROR UNTIL TOKYO CTL INFORMED US WE WERE 5 MI S. NO CONFLICTS INVOLVED. INS #1 DID SHOW A NO UPDATE MESSAGE FOR ABOUT 1 HR ENRTE; BUT IT STILL WAS IN CLOSE AGREEMENT WITH THE OTHER 2. SUPPLEMENTAL INFO FROM ACN 211014. CAPT'S LEG INTO NGO. OUR CLRNC WAS: MORAY OTR 15 (DIRECT) SMOLT OTR 16 (DIRECT) SUNNS DIRECT OSHIMA (XAC). AS WE APCHED SMOLT; TOKYO CTL INFORMED US WE WERE IN RADAR CONTACT AND THEY SHOWED US 5 MI S OF COURSE PARALLELING OUR DESIRED TRACK. OUR CLRNC WAS DIRECT OSHIMA FROM SUNNS. I EMPHATICALLY SUGGESTED TO THE CAPT HE NEEDED TO FORGET ABOUT THE #1 INS AND JUST FLY THE AIRWAYS DIRECT TO OSHIMA; USING VOR ONLY. I STATED AGAIN; I FELT WE SHOULD REQUEST DIRECT OSHIMA; (XAC) NAVIGATE USING THE VORS ONLY; FORGET THE #1 INS AND GET READY FOR OUR FIRST DSCNT AND ARR IN NGO. THE TOP OF DSCNT POINT WAS WITH A FEW MI OF XAC. HE WAS FOOLING AROUND; ATTEMPTING TO UPDATE AN INS WHEN; WE SHOULD HAVE BEEN BUSY GETTING US BACK ON COURSE AND PREPARING FOR THE DSCNT. I TRULY FELT MY INPUT WAS NOT BEING HEARD. ON THE RETURN LEG FROM NGO TO HNL I BROUGHT THE SUBJECT UP. HE QUICKLY CHANGED THE SUBJECT. I FELT I WAS NOT BEING HEARD. A SERIOUS LACK OF CRM WAS HAPPENING.