Narrative:

The situation was a possible navigation error on a random route over the north atlantic. The possible error occurred at 52N/50W which is where we thought we were cleared to, while ATC thought we were cleared to 50N/50W. The confusion about our clearance started shortly after takeoff from madrid. I was acting as the internation officer (the 3RD pilot on a 2 pilot airplane), and called shanwick radio on HF to obtain our oceanic clearance. We had been told by our dispatcher that communication problems existed in this area, and the HF reception was very poor. I had to have our clearance repeated several times to be sure of our route. The clearance was over 50N/50W, which was a change to our filed route. The first officer monitored the clearance and confirmed the routing. Shortly thereafter, madrid control issued a 'revised clearance' on VHF which the captain copied and the first officer monitored. This 'revised clearance' was the same as the one I received on the HF from shanwick, except the position of 50N/50W was replaced by 52N/50W. 52N/50W was part of our filed route. The clearance over 52N/50W given to us by madrid control was loaded in the FMC and flown. When we made our position report at 52N/50W to gander, they questioned our position and clearance. The first officer and I did not question the revised clearance, as we are both new to international flying with approximately 4 trips each, and are accustomed to route change in the united states due to our congested airspace. Our very experienced captain also did not question our 'revised clearance'. Looking back on it, I think we should have questioned the clearance madrid gave us, since it was different from the one I had just received from shanwick. Part of the problem was we were very busy preparing for oceanic entry, replaning, loading, FMC's, filling out flight logs, fuel logs, checking ETA's. Supplemental information from acn 136890: the shanwick clearance had us crossing 50N/50W whereas the madrid control clearance had us crossing 52N/50W. The 'revised clearance' received from madrid was flown and all position reports were based on that clearance. After reporting at 52N/50W an air carrier flight notified ATC that it was several minutes from 52N/50W and questioned whether our flight should be at 52N/50W. ATC (gander) then informed us that we were supposed to be at 50N/50W and that we had made position reports indicating that we planned to cross 50N/50W. In fact, our position reports indicated that we planned to cross 52N/50W as cleared by madrid control.

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Original NASA ASRS Text

Title: GROSS NAVIGATION ERROR.

Narrative: THE SITUATION WAS A POSSIBLE NAV ERROR ON A RANDOM ROUTE OVER THE NORTH ATLANTIC. THE POSSIBLE ERROR OCCURRED AT 52N/50W WHICH IS WHERE WE THOUGHT WE WERE CLRED TO, WHILE ATC THOUGHT WE WERE CLRED TO 50N/50W. THE CONFUSION ABOUT OUR CLRNC STARTED SHORTLY AFTER TKOF FROM MADRID. I WAS ACTING AS THE INTERNATION OFFICER (THE 3RD PLT ON A 2 PLT AIRPLANE), AND CALLED SHANWICK RADIO ON HF TO OBTAIN OUR OCEANIC CLRNC. WE HAD BEEN TOLD BY OUR DISPATCHER THAT COM PROBLEMS EXISTED IN THIS AREA, AND THE HF RECEPTION WAS VERY POOR. I HAD TO HAVE OUR CLRNC REPEATED SEVERAL TIMES TO BE SURE OF OUR ROUTE. THE CLRNC WAS OVER 50N/50W, WHICH WAS A CHANGE TO OUR FILED ROUTE. THE F/O MONITORED THE CLRNC AND CONFIRMED THE ROUTING. SHORTLY THEREAFTER, MADRID CTL ISSUED A 'REVISED CLRNC' ON VHF WHICH THE CAPT COPIED AND THE F/O MONITORED. THIS 'REVISED CLRNC' WAS THE SAME AS THE ONE I RECEIVED ON THE HF FROM SHANWICK, EXCEPT THE POSITION OF 50N/50W WAS REPLACED BY 52N/50W. 52N/50W WAS PART OF OUR FILED ROUTE. THE CLRNC OVER 52N/50W GIVEN TO US BY MADRID CTL WAS LOADED IN THE FMC AND FLOWN. WHEN WE MADE OUR POSITION REPORT AT 52N/50W TO GANDER, THEY QUESTIONED OUR POSITION AND CLRNC. THE F/O AND I DID NOT QUESTION THE REVISED CLRNC, AS WE ARE BOTH NEW TO INTERNATIONAL FLYING WITH APPROX 4 TRIPS EACH, AND ARE ACCUSTOMED TO ROUTE CHANGE IN THE UNITED STATES DUE TO OUR CONGESTED AIRSPACE. OUR VERY EXPERIENCED CAPT ALSO DID NOT QUESTION OUR 'REVISED CLRNC'. LOOKING BACK ON IT, I THINK WE SHOULD HAVE QUESTIONED THE CLRNC MADRID GAVE US, SINCE IT WAS DIFFERENT FROM THE ONE I HAD JUST RECEIVED FROM SHANWICK. PART OF THE PROBLEM WAS WE WERE VERY BUSY PREPARING FOR OCEANIC ENTRY, REPLANING, LOADING, FMC'S, FILLING OUT FLT LOGS, FUEL LOGS, CHECKING ETA'S. SUPPLEMENTAL INFORMATION FROM ACN 136890: THE SHANWICK CLRNC HAD US XING 50N/50W WHEREAS THE MADRID CTL CLRNC HAD US XING 52N/50W. THE 'REVISED CLRNC' RECEIVED FROM MADRID WAS FLOWN AND ALL POSITION REPORTS WERE BASED ON THAT CLRNC. AFTER REPORTING AT 52N/50W AN ACR FLT NOTIFIED ATC THAT IT WAS SEVERAL MINUTES FROM 52N/50W AND QUESTIONED WHETHER OUR FLT SHOULD BE AT 52N/50W. ATC (GANDER) THEN INFORMED US THAT WE WERE SUPPOSED TO BE AT 50N/50W AND THAT WE HAD MADE POSITION REPORTS INDICATING THAT WE PLANNED TO CROSS 50N/50W. IN FACT, OUR POSITION REPORTS INDICATED THAT WE PLANNED TO CROSS 52N/50W AS CLRED BY MADRID CTL.

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.