Narrative:

On an oceanic crossing from shannon, ireland (einn) to gander, ganada (cyqx). On jun/xx/94 we lost both of our vlfirst officermega navigation system at position N5400.0 W03000.0. The time was about XA09Z. The captain told me to inform gander radio that we lost our #1 and #2 vlfirst officermega navigation system. I informed gander radio of our status. They asked if we were still able to maintain course navigation. The captain said yes we were, through the FMS system. I relayed that information to gander radio. They said fine and the flight continued as normal until we got to N4900.0 W0500.0. That is when we were put into radar contact by gander center. They said we were 40 mi north of course. They also said they would have to file a gross navigation error report. At that point we were receiving gander VOR and proceeded direct gander using VOR navigation. The flight continued normal and landed at gander at XB47Z. During the portion of the flight where the vlfirst officermegas were failed, we naved using FMS #1 and dead reckoning. Vlfirst officermega #1 came back on line for a short time only to fail later on. Supplemental information from acn 275878: when we called for our oceanic clearance it was not the same as our computerized flight plan, so we made the changes in our FMS and proceeded on with our flight. The flight was normal until just past N5400.0 W03000.0 when we got annunciation on our FMS's that vlfirst officermega failed, so we checked our status pages and found that both vlfirst officermegas had lost their position and shortly after that #1 system came back on line and #2 system went into dr. We contacted gander radio and reported that we had lost both of our vlfirst officermega system. They asked if we could maintain navigation for the remainder of the crossing and I told the copilot to report that we could because #1 had come back on line by this time and our heading, times, and distances had not changes on the FMS page. I felt that #1 vlfirst officermega was giving some information to the FMS position even though the #1 vlfirst officermega position was inaccurate. I knew that with no information from the vlfirst officermega to the FMS the system would start to degrade, but since the #1 vlfirst officermega was back on line it would help us with our navigation and we could make a safe crossing. That is why I made the statement I could maintain navigation. #1 vlfirst officermega failed for another short period and came back on. #1 never stayed in dr. We made our plots on the north atlantic plotting chart and the #1 FMS did show us on course so I felt confident we were okay. We got a wind update at 40 west for plotting purposes. If I were to do it over again I would have communicated a lot more with gander radio about the problem. Communications is a key factor. I would not have relied so much on the FMS and spent more time on pilotage. I talked with gander center and there were no conflicts with any other aircraft. Our aircraft is equipped with TCASII and that would have given us information on any other aircraft in our area. Both system have worked normal since the occurrence. We have also sent them back to the factory for checks and are waiting for their report. We also checked with the coast guard on any problems with the vlfirst officermega system that day and they said all was normal.

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Original NASA ASRS Text

Title: NAV ERROR. HDG TRACK POS DEV.

Narrative: ON AN OCEANIC XING FROM SHANNON, IRELAND (EINN) TO GANDER, GANADA (CYQX). ON JUN/XX/94 WE LOST BOTH OF OUR VLF/OMEGA NAV SYS AT POS N5400.0 W03000.0. THE TIME WAS ABOUT XA09Z. THE CAPT TOLD ME TO INFORM GANDER RADIO THAT WE LOST OUR #1 AND #2 VLF/OMEGA NAV SYS. I INFORMED GANDER RADIO OF OUR STATUS. THEY ASKED IF WE WERE STILL ABLE TO MAINTAIN COURSE NAV. THE CAPT SAID YES WE WERE, THROUGH THE FMS SYS. I RELAYED THAT INFO TO GANDER RADIO. THEY SAID FINE AND THE FLT CONTINUED AS NORMAL UNTIL WE GOT TO N4900.0 W0500.0. THAT IS WHEN WE WERE PUT INTO RADAR CONTACT BY GANDER CTR. THEY SAID WE WERE 40 MI N OF COURSE. THEY ALSO SAID THEY WOULD HAVE TO FILE A GROSS NAV ERROR RPT. AT THAT POINT WE WERE RECEIVING GANDER VOR AND PROCEEDED DIRECT GANDER USING VOR NAV. THE FLT CONTINUED NORMAL AND LANDED AT GANDER AT XB47Z. DURING THE PORTION OF THE FLT WHERE THE VLF/OMEGAS WERE FAILED, WE NAVED USING FMS #1 AND DEAD RECKONING. VLF/OMEGA #1 CAME BACK ON LINE FOR A SHORT TIME ONLY TO FAIL LATER ON. SUPPLEMENTAL INFO FROM ACN 275878: WHEN WE CALLED FOR OUR OCEANIC CLRNC IT WAS NOT THE SAME AS OUR COMPUTERIZED FLT PLAN, SO WE MADE THE CHANGES IN OUR FMS AND PROCEEDED ON WITH OUR FLT. THE FLT WAS NORMAL UNTIL JUST PAST N5400.0 W03000.0 WHEN WE GOT ANNUNCIATION ON OUR FMS'S THAT VLF/OMEGA FAILED, SO WE CHKED OUR STATUS PAGES AND FOUND THAT BOTH VLF/OMEGAS HAD LOST THEIR POS AND SHORTLY AFTER THAT #1 SYS CAME BACK ON LINE AND #2 SYS WENT INTO DR. WE CONTACTED GANDER RADIO AND RPTED THAT WE HAD LOST BOTH OF OUR VLF/OMEGA SYS. THEY ASKED IF WE COULD MAINTAIN NAV FOR THE REMAINDER OF THE XING AND I TOLD THE COPLT TO RPT THAT WE COULD BECAUSE #1 HAD COME BACK ON LINE BY THIS TIME AND OUR HDG, TIMES, AND DISTANCES HAD NOT CHANGES ON THE FMS PAGE. I FELT THAT #1 VLF/OMEGA WAS GIVING SOME INFO TO THE FMS POS EVEN THOUGH THE #1 VLF/OMEGA POS WAS INACCURATE. I KNEW THAT WITH NO INFO FROM THE VLF/OMEGA TO THE FMS THE SYS WOULD START TO DEGRADE, BUT SINCE THE #1 VLF/OMEGA WAS BACK ON LINE IT WOULD HELP US WITH OUR NAV AND WE COULD MAKE A SAFE XING. THAT IS WHY I MADE THE STATEMENT I COULD MAINTAIN NAV. #1 VLF/OMEGA FAILED FOR ANOTHER SHORT PERIOD AND CAME BACK ON. #1 NEVER STAYED IN DR. WE MADE OUR PLOTS ON THE NORTH ATLANTIC PLOTTING CHART AND THE #1 FMS DID SHOW US ON COURSE SO I FELT CONFIDENT WE WERE OKAY. WE GOT A WIND UPDATE AT 40 W FOR PLOTTING PURPOSES. IF I WERE TO DO IT OVER AGAIN I WOULD HAVE COMMUNICATED A LOT MORE WITH GANDER RADIO ABOUT THE PROB. COMS IS A KEY FACTOR. I WOULD NOT HAVE RELIED SO MUCH ON THE FMS AND SPENT MORE TIME ON PILOTAGE. I TALKED WITH GANDER CTR AND THERE WERE NO CONFLICTS WITH ANY OTHER ACFT. OUR ACFT IS EQUIPPED WITH TCASII AND THAT WOULD HAVE GIVEN US INFO ON ANY OTHER ACFT IN OUR AREA. BOTH SYS HAVE WORKED NORMAL SINCE THE OCCURRENCE. WE HAVE ALSO SENT THEM BACK TO THE FACTORY FOR CHKS AND ARE WAITING FOR THEIR RPT. WE ALSO CHKED WITH THE COAST GUARD ON ANY PROBS WITH THE VLF/OMEGA SYS THAT DAY AND THEY SAID ALL WAS NORMAL.

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.