A B747F 30 NM OFF COURSE ENRTE TO ANC IN OCEANIC AIRSPACE.

Narrative

WE WERE ON A SCHEDULED FLT FROM NARITA TO ANC AND WERE TOLD BY SAN FRANCISCO TO CONTACT ZAN AT PLADO INTXN ON VHF. ABOUT 4-5 MINS BEFORE PLADO; ZAN CALLED US UP ON THE VHF FREQ WHICH WE AT THIS TIME WERE MONITORING. JUST AFTER THAT; I NOTICED THAT THE WAYPOINT ALERT LIGHT ON THE INS CAME ON INDICATING WE WERE CLOSE TO XING OUR NEXT WAYPOINT. HOWEVER; WHEN I GLANCED AT THE FO'S INS I SAW THAT WE WERE STILL 30+ MI FROM PLADO INTXN WITH NEARLY 4 MINS LEFT TO XING. I STARTED TO DISCUSS THIS SIT WITH THE FO AND THE FE. (WE SEE THIS A LOT IF YOU'RE BEING RADAR VECTORED AND PASS ABEAM A WAYPOINT INSTEAD OF OVER IT.) HOWEVER; BEFORE WE COULD FINISH ANALYZING THE SIT; ZAN CALLED US BACK AND TOLD US WE WERE RADAR IDENTED AND S OF COURSE. OUR INS CONFIRMED THAT WE WERE BTWN 28-29 NM OFF. WE CONFIRMED THAT WITH THE CTLR AND TOLD HIM WE WOULD CORRECT BACK ON COURSE. WE ALSO NOTICED THAT THE AUTOPLT SELECTOR SWITCH WAS IN HDG INSTEAD OF INS. WE MADE THE CORRECTION AND THE REST OF THE FLT WAS NORMAL.