GROSS NAV ERROR IN OVERWATER OP.

Narrative

DEPARTED EWR ON A RTE OVER WATER TO SAN JUAN WITH CLRNC AS FOLLOWS. EWR #4 TO DIXIE; V276 PROP 1 DIRECT OWEN3 DIRECT LINND DIRECT CHAMP A-300 KRAFT A-300 PLING RT 7 DDP SJA 33000 FT. FLEW THE DEP AND COMPARED OWEN3 INTXN ON THE OMEGA WITH JFK 150 DEG RADIAL AT 65 MI. ALSO; DID A CHK AT CHAMP WITH THE SIE 131 DEG RADIAL AT .75 MI; CHKED OK. THEN NAVIGATED BY OMEGA CONNECTED TO THE AUTOPLT MAKING ALL REQUIRED CONFIRMING CHKS. ALL CHKS SHOWED US TRACKING ON COURSE. BECAME SUSPICIOUS WHEN JUST PRIOR TO KRAFT TUNED DDP BEACON AND NEEDLE SHOWED CONSIDERABLE TO L OF NOSE. THEN TUNED GTK VOR AND CONFIRMED WE WERE APPROX 140 MI W OF COURSE. BEGAN TRYING CONTACT WITH ZNY AND ZSU. FINALLY CONTACTED ZMA ON 132.3. ZMA WAS TRACKING US ALREADY AND KNEW EXACTLY WHO WE WERE. THEY GAVE US OUR EXACT COORDINATES; WHICH I FAILED TO RECORD BUT LOOKING AT THE POS FUNCTION OF THE OMEGA THERE WAS; I NOTED; ABOUT A 3 DEG LONGITUDE DIFFERENCE. PLOTTING THE POS COORDINATED OF THE OMEGA IT STILL SHOWED US TRACKING ON COURSE; WHEN IN FACT WE WERE APPROX 140 MI TO THE W. ZMA GAVE US VECTORS FOR DDP BEACON AND WE NAVIGATED BY RADIO AIDS TO SAN JUAN. A BACKUP SYS OR 2 WOULD HAVE MORE THAN LIKELY AIDED IN SPOTTING THE INSIDIOUS ERROR OF THIS OMEGA. RPTED TO MAINT AND ACFT NOT USED FOR NON NAVAID NAV. SUPPLEMENTAL INFORMATION FROM ACN 260562: FLT WAS SELCAL'ED TO CONFIRM POS TWICE.