Narrative:

On an int'l flight from tokyo to seattle we were given a clearance on the ground that differed from our filed and computer flight plan route. Because of the addition of the point approximately 38 mi off of our filed route and our failure to notice the change we ended up approximately 25 mi off of our cleared route. What caused me to notice the problem was an air carrier Y flight behind us reported the point we had just checked except he estimated a point different than the one we had just estimated. We corrected back to course at that point west/O notifying ATC because we did not feel our doing so would cause a hazard. I feel the problem arose partly because ATC did not identify our routing as a reroute as they often do and partly because we (the crew) did not compare the cleared and copied route with the filed/computer flight plan route. Additionally, when I estimated the next point, ATC did not catch the discrepancy. In the future I plan to copy the clearance immediately next to the filed routing for easy comparison. Supplemental information from acn 94002: change in flight plan by ATC controller west/O a comment by him that the flight plan was changed. Ground called with a problem at same time clearance was coming across. First officer copied the clearance.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR WDB DEVIATED FROM CLRNC ROUTE ON EXTENDED OVERWATER OPERATION.

Narrative: ON AN INT'L FLT FROM TOKYO TO SEATTLE WE WERE GIVEN A CLRNC ON THE GND THAT DIFFERED FROM OUR FILED AND COMPUTER FLT PLAN ROUTE. BECAUSE OF THE ADDITION OF THE POINT APPROX 38 MI OFF OF OUR FILED ROUTE AND OUR FAILURE TO NOTICE THE CHANGE WE ENDED UP APPROX 25 MI OFF OF OUR CLRED ROUTE. WHAT CAUSED ME TO NOTICE THE PROB WAS AN ACR Y FLT BEHIND US RPTED THE POINT WE HAD JUST CHKED EXCEPT HE ESTIMATED A POINT DIFFERENT THAN THE ONE WE HAD JUST ESTIMATED. WE CORRECTED BACK TO COURSE AT THAT POINT W/O NOTIFYING ATC BECAUSE WE DID NOT FEEL OUR DOING SO WOULD CAUSE A HAZARD. I FEEL THE PROB AROSE PARTLY BECAUSE ATC DID NOT IDENT OUR ROUTING AS A REROUTE AS THEY OFTEN DO AND PARTLY BECAUSE WE (THE CREW) DID NOT COMPARE THE CLRED AND COPIED RTE WITH THE FILED/COMPUTER FLT PLAN RTE. ADDITIONALLY, WHEN I ESTIMATED THE NEXT POINT, ATC DID NOT CATCH THE DISCREPANCY. IN THE FUTURE I PLAN TO COPY THE CLRNC IMMEDIATELY NEXT TO THE FILED ROUTING FOR EASY COMPARISON. SUPPLEMENTAL INFO FROM ACN 94002: CHANGE IN FLT PLAN BY ATC CTLR W/O A COMMENT BY HIM THAT THE FLT PLAN WAS CHANGED. GND CALLED WITH A PROB AT SAME TIME CLRNC WAS COMING ACROSS. F/O COPIED THE CLRNC.

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.