Narrative:

After crossing the atlantic we made contact with moncton center at prawn intersection. Their radar had us 8 mi south of course. The #1 autoplt was tracking off of the #1 INS. The #3 INS showed us approximately 8 mi left of course, therefore we switched the autoplt over to the #3 INS. Within a 30 min time frame we were given 2 reroute clrncs, which we had to reprogram into all 3 INS's. Shortly after eddit intersection first officer noticed the discrepancy. His course showed us deviating north of course. I reentered the leg (eddit to tufdy) into #1 and #3 INS's. I got an indication to turn right and started the turn. First officer INS (#3) showed a turn to the south was required. We were sorting out the problem when moncton center regained radar contact on us and advised we were 80 mi north of course. They gave us a vector heading for tufdy and when we entered direct tufdy in all 3 INS's they agreed with the vector heading. Somewhere in the remote loading process (automatically loading information from one INS into the other 2 INS's) and changing the autoplt over to the #3 INS, the compass did not properly slave and continued to take us north of course. Supplemental information from acn 117798: prior to ykl we were given a reroute by moncton center while in radar contact. After the reroute was read back and confirmed on our maps we were told to give a position report over ykl. This was our first indication that radar contact was lost. I put the new track into the #1 INS--the #3 INS was now flying the aircraft. The captain switched to the #3 INS because throughout the atlantic crossing the #3 INS appeared to be tracking the best. After ykl we were told to contact moncton center on 133.5 and on initial contact moncton advised, 'stand by for radar identify.' I thought we would be idented very soon so I stopped plotting our position. The 2 track changes we received came quickly, therefore we did not immediately xload the new route into the #2 and #3 INS. This delay occurred because we were busy finding thee fixes on our maps and confirming them amongst ourselves and what was entered in the #1 INS. We discovered an error somewhere north of eddit intersection. While trying to sort out the problem we selected a leg in the #1 INS of eddit to tufdy and began flying the displayed course to the north. When I selected the same leg of eddit to tufdy on the #2 INS it indicated a turn to the south was required to get back on course. At that point we were unsure which INS was correct.

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Original NASA ASRS Text

Title: ACR FLT CREW EXPERIENCES A GROSS NAVIGATION ERROR UPON ENTERING CANADIAN AIRSPACE AFTER AN OCEANIC CROSSING.

Narrative: AFTER XING THE ATLANTIC WE MADE CONTACT WITH MONCTON CENTER AT PRAWN INTXN. THEIR RADAR HAD US 8 MI S OF COURSE. THE #1 AUTOPLT WAS TRACKING OFF OF THE #1 INS. THE #3 INS SHOWED US APPROX 8 MI LEFT OF COURSE, THEREFORE WE SWITCHED THE AUTOPLT OVER TO THE #3 INS. WITHIN A 30 MIN TIME FRAME WE WERE GIVEN 2 REROUTE CLRNCS, WHICH WE HAD TO REPROGRAM INTO ALL 3 INS'S. SHORTLY AFTER EDDIT INTXN F/O NOTICED THE DISCREPANCY. HIS COURSE SHOWED US DEVIATING N OF COURSE. I REENTERED THE LEG (EDDIT TO TUFDY) INTO #1 AND #3 INS'S. I GOT AN INDICATION TO TURN RIGHT AND STARTED THE TURN. F/O INS (#3) SHOWED A TURN TO THE S WAS REQUIRED. WE WERE SORTING OUT THE PROB WHEN MONCTON CENTER REGAINED RADAR CONTACT ON US AND ADVISED WE WERE 80 MI N OF COURSE. THEY GAVE US A VECTOR HDG FOR TUFDY AND WHEN WE ENTERED DIRECT TUFDY IN ALL 3 INS'S THEY AGREED WITH THE VECTOR HDG. SOMEWHERE IN THE REMOTE LOADING PROCESS (AUTOMATICALLY LOADING INFO FROM ONE INS INTO THE OTHER 2 INS'S) AND CHANGING THE AUTOPLT OVER TO THE #3 INS, THE COMPASS DID NOT PROPERLY SLAVE AND CONTINUED TO TAKE US N OF COURSE. SUPPLEMENTAL INFO FROM ACN 117798: PRIOR TO YKL WE WERE GIVEN A REROUTE BY MONCTON CENTER WHILE IN RADAR CONTACT. AFTER THE REROUTE WAS READ BACK AND CONFIRMED ON OUR MAPS WE WERE TOLD TO GIVE A POS RPT OVER YKL. THIS WAS OUR FIRST INDICATION THAT RADAR CONTACT WAS LOST. I PUT THE NEW TRACK INTO THE #1 INS--THE #3 INS WAS NOW FLYING THE ACFT. THE CAPT SWITCHED TO THE #3 INS BECAUSE THROUGHOUT THE ATLANTIC XING THE #3 INS APPEARED TO BE TRACKING THE BEST. AFTER YKL WE WERE TOLD TO CONTACT MONCTON CENTER ON 133.5 AND ON INITIAL CONTACT MONCTON ADVISED, 'STAND BY FOR RADAR IDENT.' I THOUGHT WE WOULD BE IDENTED VERY SOON SO I STOPPED PLOTTING OUR POS. THE 2 TRACK CHANGES WE RECEIVED CAME QUICKLY, THEREFORE WE DID NOT IMMEDIATELY XLOAD THE NEW ROUTE INTO THE #2 AND #3 INS. THIS DELAY OCCURRED BECAUSE WE WERE BUSY FINDING THEE FIXES ON OUR MAPS AND CONFIRMING THEM AMONGST OURSELVES AND WHAT WAS ENTERED IN THE #1 INS. WE DISCOVERED AN ERROR SOMEWHERE N OF EDDIT INTXN. WHILE TRYING TO SORT OUT THE PROB WE SELECTED A LEG IN THE #1 INS OF EDDIT TO TUFDY AND BEGAN FLYING THE DISPLAYED COURSE TO THE N. WHEN I SELECTED THE SAME LEG OF EDDIT TO TUFDY ON THE #2 INS IT INDICATED A TURN TO THE S WAS REQUIRED TO GET BACK ON COURSE. AT THAT POINT WE WERE UNSURE WHICH INS WAS CORRECT.

Data retrieved from NASA's ASRS site as of August 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.