Narrative:

On russian airway G212 over xr, controller said we were 5 KM right of course. Shortly thereafter, he said 10 KM right of course. My first officer and I checked all we could and we replied we were on course. The next check point controller said 5 KM right of course. We tuned all NDB's and watched another aircraft on TCASII about 4 mi left of us. I noticed the NDB at the next fix left of us. I decided to fly a left 2 NM offset. About 1 hour later, I flew 3 NM left offset for the remainder of russian airspace because other aircraft were still 1 or 2 mi left of us, and NDB still showed us slightly right of course. When calling zan over frenk, we had some DME updating on the FMC's. Prior to this, 'IRS only' was our navigation. I deleted the left 3 NM offset near frenk, and zan showed us on course in zan. With no DME updating of FMC's I should have declared 'navigation system unreliable' to ATC. I have become too confident in the navigation system over yrs of accuracy. I do not know why russian ATC said 5 KM and then 10 KM shortly after -- maybe to get our attention better. We asked russian ATC after xr and flying left offset if we were on course. They never had a problem with our course after that. The left offset corrected the course, but I should have said 'navigation system unreliable.'

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Original NASA ASRS Text

Title: A B747-400 PIC IS ADVISED BY RUSSIAN RADAR CTLR THAT HE IS 3-6 MI R OF THE CTRLINE OF AIRWAY G212, XR, FO.

Narrative: ON RUSSIAN AIRWAY G212 OVER XR, CTLR SAID WE WERE 5 KM R OF COURSE. SHORTLY THEREAFTER, HE SAID 10 KM R OF COURSE. MY FO AND I CHKED ALL WE COULD AND WE REPLIED WE WERE ON COURSE. THE NEXT CHK POINT CTLR SAID 5 KM R OF COURSE. WE TUNED ALL NDB'S AND WATCHED ANOTHER ACFT ON TCASII ABOUT 4 MI L OF US. I NOTICED THE NDB AT THE NEXT FIX L OF US. I DECIDED TO FLY A L 2 NM OFFSET. ABOUT 1 HR LATER, I FLEW 3 NM L OFFSET FOR THE REMAINDER OF RUSSIAN AIRSPACE BECAUSE OTHER ACFT WERE STILL 1 OR 2 MI L OF US, AND NDB STILL SHOWED US SLIGHTLY R OF COURSE. WHEN CALLING ZAN OVER FRENK, WE HAD SOME DME UPDATING ON THE FMC'S. PRIOR TO THIS, 'IRS ONLY' WAS OUR NAV. I DELETED THE L 3 NM OFFSET NEAR FRENK, AND ZAN SHOWED US ON COURSE IN ZAN. WITH NO DME UPDATING OF FMC'S I SHOULD HAVE DECLARED 'NAV SYS UNRELIABLE' TO ATC. I HAVE BECOME TOO CONFIDENT IN THE NAV SYS OVER YRS OF ACCURACY. I DO NOT KNOW WHY RUSSIAN ATC SAID 5 KM AND THEN 10 KM SHORTLY AFTER -- MAYBE TO GET OUR ATTN BETTER. WE ASKED RUSSIAN ATC AFTER XR AND FLYING L OFFSET IF WE WERE ON COURSE. THEY NEVER HAD A PROB WITH OUR COURSE AFTER THAT. THE L OFFSET CORRECTED THE COURSE, BUT I SHOULD HAVE SAID 'NAV SYS UNRELIABLE.'

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.