B747-200 flight crew reports being informed by ATC over LUNAD that the aircraft is tracking 12 KM to the right of the airway and that all company aircraft seem to exhibit the same error. The crew believes the navigation system's IRSs are old and do not have any opportunity to update in Russian airspace.
Synopsis
B747-200 flight crew reports being informed by ATC over LUNAD that the aircraft is tracking 12 KM to the right of the airway and that all company aircraft seem to exhibit the same error. The crew believes the navigation system's IRSs are old and do not have any opportunity to update in Russian airspace.
Narrative
The flight was proceeding normally until we entered the Magadan FIR; in the eastern most portion of Russia. Our flight plan had us making a 45 degree right turn at waypoint LUNAD; to track outbound to GIRLO on airway G212. The autopilot turned us about 6 miles early; this was evidenced by the coincidental parallel tracking of another aircraft on the same airway approx 3;000 FT below us. Magadan Control notified us that we were in fact 12 KILOMETERS to the right of centerline; tracking parallel. The Captain; as pilot flying; initiated a 6 mile left-of-course offset in the Litton 72; at which point the aircraft resumed the proper tracking along the airway. Furthermore; Magadan notified us that 'ALL Company aircraft are 12 kilometers off course at this point.' He asked us if we had issues with our autopilot. No further action was taken until we entered Anchorage's airspace; as that was the first opportunity the navigation system had to pick up a VOR for updating. There are no usable VOR's along the entire Russian landscape; we were flying un-updated navigation system for maybe 5 hours at that point. The event occurred because we are flying old and outdated navigation equipment in areas of the world where they should not be used. After leaving Japan's airspace; there is not one single opportunity to update the navigation system; as there are no VOR's ANYWHERE along the course of flight. These navigation systems drift a LOT; as evidenced by the accuracy check performed upon landing; #1 INS had an error of 2 miles; #2 INS had an error of 7 miles; and #3 INS had an error of 10 miles.
Second reporter narrative
Upon entering the Magadan FIR; all systems were normal until reaching navigation waypoint LUNAD. At that point we were supposed to track outbound from LUNAD to GIRLO on G212. This is what the autopilot did; however ATC called us stating that we were 12 kilometers (5.8 miles) right of track. After being advised by ATC of our course deviation; I had placed a position hold on all three INS to compare the differences between each other. The differences were as much as 10 minutes apart both in latitude and longitude. Magadan ATC advised us to correct to the left to reestablish the course. With autopilot 'A' engaged; INS #1 was set to navigate with a cross track deviation to the left of 5.8 miles; thus allowing to navigation back on center line track. Once reestablished; we continued on with the cross track deviation until reaching an updateable VOR. Once [each] INS was updated; we continued onto our destination without any further incident. Since most other companies are navigating with GPS updating; aircraft that are not exactly on centerline of the airway stand out more. The following statement was mentioned by Magadan ATC: 'Company flight; for your information all Company aircraft have been navigating right of course in our airspace. Are there problems with your autopilot?' My response was simply apologizing for the deviation and mentioning that our equipment is not GPS updateable. Upon blocking in at our destination airport; an accuracy test was done on all three INS. INS #1 had an error of 2 miles; INS #2 had an error of 7 miles; and INS #3 had an error of 10 miles. An INS' position drifts over time and there were no VORs to update off of. In time; the INS gyro begins to drift to the point where there is a significant discrepancy in the actual aircraft's position. The aircraft's INS should be upgraded to platforms with FMS and GPS updating. With the GPS update feature; the autopilot will still maintain correct navigation guidance even if the INS begins to drift.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.