A DC10 FLC STRAYS OFF COURSE OVER CANADA WHEN FAILING TO UPDATE THEIR INS FOR OVER 5 HRS ON A FLT FROM EUROPE. DEV NOTED BY CTLR AT CZEG; AB.

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WHILE I; THE CAPT; WAS IN BATHROOM; YEG CTR ADVISED ACFT WAS S OF COURSE ON NCAC; 190 NM NE OF YMM. HDG WAS USED TO RETURN ACFT TO COURSE WHEN YMM VORTAC WAS RECEIVABLE. AN INS UPDATE HAD NOT BEEN ACCOMPLISHED FOR APPROX 5 HRS. AFTER AN UPDATE WAS DONE SW OF YMM; INS NAV WAS RE-ESTABLISHED. AFTER SHUTDOWN; #2 AND #3 INS UNITS WERE OUT OF DRIFT ERROR TOLERANCE. AN ACFT LOG ENTRY WAS MADE. SUPPLEMENTAL INFO FROM ACN 818955: PLACE VOR/DME FURTHER IN NORTHERN CANADA FOR UPDATING. SUPPLEMENTAL INFO FROM ACN 518943: ALL 3 INS'S SHOWED DIRECTLY ON CTRLINE; WITH ALL COORDINATES FOR YSF AND YMM AGREEING WITH BOTH FLT PLAN AND CHART. LUTTEN YMM VOR CAME INTO RANGE; IT SHOWED US ON THE 032 DEG RADIAL AT 140 DME; INSTEAD OF THE EXPECTED 024 DEG RADIAL. CHKING INS POS 'INERT COMPARE' PAGE SHOWED ALL 3 INS'S WITH UP TO 12 NM OFF ON UPDT. AFTER RECEIVING VOR STATIONS TO RECOMMENCE UPDATING; #1 INS UPDT ERROR REDUCED TO LESS THAN 1.0; WHILE #2 AND #3 INITIALLY REDUCED; THEN INCREASED. THE #2 ERROR WAS GREATER THAN 18 AND #3 ERROR WAS GREATER THAN 15.