Narrative:

After filing at an overseas location, using provided computer flight plan, we were assigned an alternate north atlantic track (nata) in flight. This was the northernmost track. Coordinates prior to missed point were N58 degrees W050 degrees. Next point was to be porgy (N56-19 W058-USA.). Moncton center reported that we crossed around 57 degrees north W060 degrees. This would have been near prawn. No conflict with other traffic occurred, as verified by moncton center. Rechked position off schefferville, 3 1/2 NM instrument error. Coordinates in instrument memory showed proper coordinates. Verified by crew. Moncton asked for porgy coordinates and verified proper nfo. Approaching 050 degrees, aircraft commander left for short break. Due to programming on domestic leg, ocean plotting, 10 minute plot was inadvertently forgotten. During the entire ocean flight, the autoplt was connected to the INS/fsas system. The cause of the navigation error is still under investigation. Unsure if crew error in operation or programming of INS/fsas or internal fsas problem caused error. Crew missed 10 minute plot which could have saved crew from navigation error. Note no inland navigation bearings available at or near porgy. Also, since we did not have a computer flight plan of route, all INS data appeared reasonable. The importance of the 10 minute plot was verified by this event.

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Original NASA ASRS Text

Title: MONCTON CENTER ALLEGES MIL FLT WAS 120 NM WEST OF REPORTED POSITION. FLT CREW NAVIGATION CHECK SHOWED 3-4 NM ERROR.

Narrative: AFTER FILING AT AN OVERSEAS LOCATION, USING PROVIDED COMPUTER FLT PLAN, WE WERE ASSIGNED AN ALTERNATE NORTH ATLANTIC TRACK (NATA) IN FLT. THIS WAS THE NORTHERNMOST TRACK. COORDINATES PRIOR TO MISSED POINT WERE N58 DEGS W050 DEGS. NEXT POINT WAS TO BE PORGY (N56-19 W058-U.S.A.). MONCTON CENTER RPTED THAT WE CROSSED AROUND 57 DEGS N W060 DEGS. THIS WOULD HAVE BEEN NEAR PRAWN. NO CONFLICT WITH OTHER TFC OCCURRED, AS VERIFIED BY MONCTON CENTER. RECHKED POS OFF SCHEFFERVILLE, 3 1/2 NM INST ERROR. COORDINATES IN INST MEMORY SHOWED PROPER COORDINATES. VERIFIED BY CREW. MONCTON ASKED FOR PORGY COORDINATES AND VERIFIED PROPER NFO. APCHING 050 DEGS, ACFT COMMANDER LEFT FOR SHORT BREAK. DUE TO PROGRAMMING ON DOMESTIC LEG, OCEAN PLOTTING, 10 MINUTE PLOT WAS INADVERTENTLY FORGOTTEN. DURING THE ENTIRE OCEAN FLT, THE AUTOPLT WAS CONNECTED TO THE INS/FSAS SYS. THE CAUSE OF THE NAV ERROR IS STILL UNDER INVESTIGATION. UNSURE IF CREW ERROR IN OPERATION OR PROGRAMMING OF INS/FSAS OR INTERNAL FSAS PROB CAUSED ERROR. CREW MISSED 10 MINUTE PLOT WHICH COULD HAVE SAVED CREW FROM NAV ERROR. NOTE NO INLAND NAV BEARINGS AVAILABLE AT OR NEAR PORGY. ALSO, SINCE WE DID NOT HAVE A COMPUTER FLT PLAN OF RTE, ALL INS DATA APPEARED REASONABLE. THE IMPORTANCE OF THE 10 MINUTE PLOT WAS VERIFIED BY THIS EVENT.

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.