ACR LGT LOST NAV CAPABILITY ON EXTENDED OVER WATER OP. PICKED UP A COMPANY FLT AND FOLLOWED IT TO SJU.

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I RECEIVED A CALL FROM NY COMMERCIAL RADIO ADVISING ME THAT ACR XX PHL-SJU WAS 150 NM S OF CHAMP AND HAD LOST BOTH OF HIS OMEGA/S. SAID THE FLT WAS GOING TO CONTINUE TO SJU. I ASKED COMMERCIAL RADIO TO GET ME A PATCH WITH ACFT. WHEN I SPOKE TO ACFT THEY SAID THEY HAD RECONSIDERED AND NOW WANTED TO LAND INSTEAD OF CONTINUING TO SJU. I ASKED IF HE COULD RETURN TO AN ARPT ON THE NE COAST. THE FLT SAID THEY WERE ONLY RECEIVING BDA ON THE ADF AND WANTED TO GO THERE. I GAVE ACFT THE BDA WX AND TOLD HIM I'D SETUP THE BDA LNDG. ABOUT 10 MIN LATER; I GOT A CALL FROM COMMERCIAL RADIO AND ACFT COMES ON TALKING WITH ATC; SAYING HE IS VISUAL WITH COMPANY ACFT AND WANTS TO FOLLOW HIM TO SJU. ATC TELLS XXX THAT IT CANNOT ASSURE HIM OF IFR SEPARATION WITH TFC. CAPT OF XXX TELLS ATC HE WILL ACCEPT RESPONSIBILITY FOR SEPARATION WITH TFC. I THEN INFORM XXX THAT SATELLITE IMAGERY SHOWS A LARGE AREA OF CIRRUS AHEAD OF HIM AND HE MIGHT NOT BE ABLE TO STAY VISUAL WITH YYY OMEGA AND THERE WAS ONLY A 2 MI DIFFERENCE AND HE WANTED TO GO ON TO SJU. XXX CONTINUED ON AND LANDED WITHOUT FURTHER INCIDENT. AFTER LNDG THE CAPT CALLED AND BRIEFED ME. HE WAS UNABLE TO GET A CLRNC FROM ATC TO BDA; SO HE MADE S TURNS AND YYY PICKED HIM UP ON THE TCASII SYS. XXX PICKED UP YYY ON THE WX RADAR. THE OMEGA/S TRACKED CORRECTLY ALL THE WAY TO SJU.