AN ACR B727 FLC BECOMES LOST WHEN THEIR OMEGA NAV GOES INTO DEAD RECKONING MODE; DUE TO INSUFFICIENT GND STATION SIGNALS; DURING AN EXTENDED WX AVOIDANCE DEV. ZNY WAS ABLE TO GIVE THEM A VECTOR AND ALSO DECLARED A FUEL EMER FOR THEM.

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WHILE NAVING ON A554 BTWN ODEAL INTXN AND KATHY INTXN; WE REQUESTED A DEV E OF COURSE DUE TO A LINE OF WX LYING W/E ACROSS OUR COURSE. THE DEV REQUESTED WAS FORWARDED TO ZNY BY NEW YORK RADIO. ZNY APPROVED DEV; E OF COURSE WITH A CLRNC TO PROCEED DIRECT TO CHAMP INTXN WHEN ABLE. UPON INITIATING R TURN; THE OMEGA NAV SYS INDICATED THAT IT NO LONGER WAS RECEIVING SUFFICIENT STATIONS TO GIVE ACCURATE POS INFO AND WENT INTO A DEAD RECKONING STATUS. REACHING THE LINE OF WX; WE FOUND IT NECESSARY TO DEV FURTHER E DUE TO ICING; TURB (MODERATE); RAIN AND LIGHTNING BEING ENCOUNTERED. ONCE CLR OF ALL WX; WE ADVISED ATC VIA NEW YORK RADIO THAT WE WERE FURTHER E THAN ANTICIPATED AND THAT WE WERE ALSO UNABLE TO PROCEED BACK TO OUR COURSE DUE TO THE FAILURE OF OUR NAV SYS. WE WERE THEN GIVEN A VHF FREQ TO CONTACT ZNY. IT TOOK SOME TIME (APPROX 10 MINS) TO ESTABLISH COM WITH ATC. ONCE COM WAS ESTABLISHED; ATC ASSIGNED A HDG OF 270 DEGS AS VECTORS TO NEWARK (ROBINSVILLE VOR) AND ADVISED US OUR POS WAS 265 NM E OF RBV VOR. WE WERE EVENTUALLY VECTORED FOR A VISUAL APCH TO RWY 4R AT EWR AND LANDED UNEVENTFULLY. WE DID NOT DECLARE AN EMER; BUT WERE ADVISED ATC HAD DECLARED US AN EMER CONDITION DUE TO OUR LOW FUEL STATUS. SUPPLEMENTAL INFO FROM ACN 374823: I WAS CONTACTED BY MY FLT FROM AUA- EWR. THEY HAD A FAILURE OF THEIR OMEGA NAV SYS AND THEY WERE NOW 225 MI OFF COURSE. WHILE FLYING NBOUND ON A554 AT APPROX KATHY INTXN; THEY DEVIATED E TO AVOID WX. SHORTLY AFTER BEGINNING THE DEV; THEIR OMEGA FAILED. WHEN ACFT WAS INBOUND TO EWR I REQUESTED PRIORITY HANDLING BY ZNY. THEY SAID THEY WOULD TREAT THIS FLT AS A FUEL EMER.