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.