A MIL TRANSPORT FLC EXPERIENCED NAV PROBS AS A RESULT OF INS AND GPS MALFUNCTIONS; AND THE USE OF INCORRECT CHARTS. THE NAVIGATOR'S MANUAL POS; WHICH WAS UTILIZED; WAS SHOWN WITH MONCTON CTR AS 50 MI N OF TRACK.

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AFTER XING THE NORTH ATLANTIC; WBOUND; MONCTON CTR MADE RADAR CONTACT AND INFORMED THE CREW THAT HE SHOWED THEM 50 MI N OF TRACK AND THAT THIS WAS A 'GROSS NAV ERROR.' THE ACFT WAS EQUIPPED WITH TACAN; VOR; ADF; INS; GPS; STELLAR; DOPPLER RADAR; GND MAPPING RADAR; AND QUALIFIED AIR FORCE NAVIGATORS DOING CELESTIAL NAV. HOWEVER; THERE WERE SEVERAL MALFUNCTIONS DISCOVERED AFTER TKOF. THE INS WAS REALIGNED SEVERAL TIMES INFLT WITH LIMITED SUCCESS; AND THE AUTOPLT STARTED MAKING SMALL UNCOMMANDED TURNS IN 'HDG SELECT' MODE (NOT COUPLED TO THE NAV SYS). THE NAVIGATORS WERE PERFORMING 'GRID NAV' WITH THE ACFT'S COMPASSES SLEWED TO THE APPROPRIATE GRID REF. HOWEVER; IT WAS DISCOVERED AFTER FLT THAT THE CHARTS BEING USED HAD THE WRONG GRID CONVERGENCE FACTOR PRINTED ON THEM. THIS WOULD APPEAR TO BE THE MOST SIGNIFICANT CONTRIBUTING FACTOR IN THIS INCIDENT. ALTHOUGH THIS ERROR; COMBINED WITH NAV SYS PROBS; LED TO THE ACTUAL NAV ERROR; IT IS UNDERSTOOD THAT THE CREW FAILED TO RPT THE SYS MALFUNCTIONS TO ATC IN ACCORDANCE WITH FAR 91.187 WHICH MAY HAVE CHANGED ATC'S TFC SEPARATION CRITERIA OR PRECLUDED OPERATING IN NAT MNPS AIRSPACE. THE HUMAN FACTORS WHICH MAY HAVE CONTRIBUTED TO OUR LACK OF JUDGEMENT AND COMPLIANCE WERE: A VERY LONG CREW DUTY DAY. THIS INCIDENT OCCURRED APPROX 13 HRS AFTER TKOF AND 16 HRS AFTER RPTING FOR DUTY. MULTIPLE 'SEAT SWAPPING' WITH EXTRA PLTS AND NAVIGATORS. ALTHOUGH NOT REQUIRED; WE HAPPENED TO HAVE 2 EXTRA PLTS AND 1 EXTRA NAVIGATOR ON THE ACFT. THERE COULD HAVE BEEN BETTER COM BTWN CREW MEMBERS SWITCHING OUT WITH EACH OTHER REGARDING WHAT ACFT SYS PROBS EXISTED AND WHAT TO DO ABOUT THEM; PARTICULARLY IN REGARD TO ATC COORD. TO PREVENT AN OCCURRENCE OF THIS TYPE OF INCIDENT I INTEND TO: 1) INFORM ATC WITHOUT DELAY OF ANY MALFUNCTIONS OF NAV; APCH; OR COM EQUIP OCCURRING INFLT. 2) ENSURE ADEQUATE PREFLT PLANNING IS CONDUCTED; WITH PARTICULAR EMPHASIS ON USING CURRENT AND CORRECT NAV CHARTS. 3) BE MORE CONSCIENTIOUS IN COORDINATING ACTIONS AND INTENTIONS WITH OTHER CREW MEMBERS; PARTICULARLY IN SITS INVOLVING SEAT SWAPPING FOR THE PURPOSE OF INFLT REST PERIODS. SUPPLEMENTAL INFO FROM ACN 303143: THE INS HAD GONE BAD AND WAS SHUT DOWN. ABEAM GREENLAND; THE ACFT WAS NO MORE THAN 5 MI TO THE R OF TRACK BASED ON A RADAR FIX OFF THE COAST OF GREENLAND. THE GPS WAS WITHIN 3 MI OF THE RADAR FIX. AFTER PROCEEDING PAST GREENLAND; THE GPS BEGAN WANDERING AND DISPLAYING ERROR CODES. NAVIGATOR HAD COMPASSES IN GRID AND WAS USING PRESSURE LOP'S FOR COURSE LINE AND SUN LOP'S FOR SPD LINE. THE LAST FIX PRIOR TO PRAWN SHOWED THE ACFT NO MORE THAN 10 MI R OF TRACK BASED ON CELESTIAL AND DOPPLER; HOWEVER; THE GPS SHOWED THE ACFT 50 MI R OF TRACK. THE NAVIGATOR FELT THE GPS WAS UNRELIABLE AND HIS MANUAL POS WAS CORRECT. THE COPLT CONTACTED MONCTON CTR; WHO QUERIED US ABOUT OUR OCEANIC CLRNC AND WHY WE WEREN'T PROCEEDING TO THE PRAWN COASTAL FIX. BIGGEST FACTOR CONTRIBUTING TO THIS INCIDENT IS FAILURE OF THE INS; ONLY PERIODIC AND SPORADIC READINGS FROM THE GPS AND AN UNSTABLE AUTOPLT.