B777 FLT CREW EXPERIENCED TRACK DEVIATION; CREW DISCOVERS ACFT IN HDG MODE RATHER THAN LNAV. THE SITUATION WAS COMPOUNDED BY VARIOUS CREW CHANGES AT THE TIME THEIR CLEARANCE WAS RECEIVED.

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APPROX 15 MINS AFTER RETURNING FROM MINE AND THE RELIEF PLT'S SECOND BREAK; WE RECEIVED A CALL FROM VANCOUVER CTR ASKING IF WE WERE PROCEEDING DIRECT TO YVR. WHEN I HAD SAT DOWN IN THE SEAT BEING THE SECOND ONE UP TO THE COCKPIT; I HAD HEARD THE TAIL END OF THE CHANGEOVER BRIEF. FOR SOME REASON I THOUGHT WE WERE GOING DIRECT TO A POINT FURTHER PAST YVR SO AT THAT POINT IT DIDN'T LOOK ODD THAT YVR WAS OFF TO THE R. AS SOON AS CTR CALLED; WE REALIZED THAT LNAV WAS NOT ENGAGED AND WE WERE ON A HDG. WE REPLIED TO CTR THAT WE WERE L OF COURSE AND HE THEN GAVE US DIRECT TO GTF. NO CONFLICT WAS CREATED AND CTR MADE NO OTHER MENTION OF IT. HE DID NOT ASK WHY; OR ANY OTHER QUERY. THE REST OF THE FLT WAS UNEVENTFUL. AFTER THE CAPT AND FO RETURNED; WE ASKED THEM ABOUT IT AND WE REALIZED THAT THEY HAD BEEN GIVEN DIRECT TO YVR JUST BEFORE THEIR BREAK STARTED AND THE CHANGEOVER OCCURRED. THEY INITIALLY STARTED TOWARDS YVR WITH HDG SELECT AND LNAV WAS NEVER ENGAGED. WE SHOULD HAVE CAUGHT IT DURING THE BRIEF AND CHANGEOVER. FROM NOW ON; THE FIRST THING I WILL DO BESIDES GETTING A GOOD BRIEF IS CHK THAT LNAV IS ENGAGED. SUPPLEMENTAL INFO FROM ACN 802944: AS WE APCHED ORNAI; VANCOUVER GAVE US THE CLRNC: 'AFTER ORNAI; YOU ARE CLRED DIRECT VANCOUVER.' THE CAPT STATED THAT HE WANTED TO INCLUDE A COUPLE OF POINTS BTWN ORNAI AND YVR SO HE SAID HE WOULD DELAY PUTTING THE DIRECT INTO THE FMC UNTIL ORNAI SO HE COULD USE THE ABEAM POINT FUNCTION AND HAVE ABEAM POINTS IN THE FMC. THE PROB HAPPENED WHEN WE GOT TO ORNAI. THE PF KICKED IT OUT OF LNAV SO AS TO USE HDG SELECT TO MAKE THE TURN. RIGHT AT THIS MOMENT; THE TIME TO SWITCH OUT WITH THE 2 RELIEF PLTS; I GOT UP THEN AND LET THE #2 RELIEF PLT TAKE HIS SEAT. HE SAID VANCOUVER HAD ASKED THEM IF THEY WERE GOING DIRECT TO YVR A WHILE AFTER WE HAD LEFT THE COCKPIT BECAUSE THEY WERE WELL L OF COURSE. AT THIS POINT; THEY DISCOVERED THE ACFT WAS STILL IN HDG MODE -- LNAV WAS NEVER RE-ENGAGED.