AN ACR B737 PLT RPTS THAT BOTH HE AND A B727 CREW HAD PROBS WITH THE PVD ILS. BOTH ACFT HAD BEEN TRACKING THE LOC IN IMC AND SUDDENLY GOT A FULL SCALE OFF COURSE INDICATION NEAR THE 'RENCH' OM. EVASIVE ACTION GAR.

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FLYING THE ILS 5 AT PVD; I INTERCEPTED AND TRACKED LOC FROM ABOUT 30 NM OUT. PASSING RENCH INTXN ON THE APCH; COMPLETED CONFIGN AND THE BEFORE LNDG CHKLIST. THE COPLT WAS FLYING WITH THE AUTOPLT ENGAGED. AS I COMPLETED THE CHKLIST; I NOTICED FULL SCALE R DEFLECTION ON BOTH CDI'S. ALMOST SIMULTANEOUSLY; BOTH FLT DIRECTORS AND THE AUTOPLT DISENGAGED. WITH NO RWY IN SIGHT; WE WENT AROUND. ON DOWNWIND; I ASKED THE CTLR IF THEY HAD ANY SIGNAL ALARMS. HE STATED THEY HAD NOT. WE LANDED THE SECOND TIME WITHOUT INCIDENT. I WAS READY TO CHALK THIS UP AS AN UNEXPLAINABLE FLUKE UNTIL A CHANCE MEETING THE NEXT DAY. AT OUR LAYOVER HOTEL; I HAD A CHAT WITH AN ACR B727 CAPT. THEY CAME IN ABOUT 7 1/2 HRS AFTER US ON THE SAME APCH; ILS 5 PVD. HE SAID THE COPLT WAS TRACKING IN ON THE LOC. AT ABOUT 8-9 MI OUT; THE CTLR QUERIED THEM SUGGESTING THEY WERE OFF COURSE. THOUGH THE CDI NEEDLE WAS CTRED AT THE TIME OF THE CALL; JUST A FEW MOMENTS LATER; IT INDICATED FULL R DEFLECTION. THEY; TOO; WENT AROUND. THEY FLEW A RADAR PATTERN AND LANDED WITHOUT INCIDENT. THE SIMILARITY OF EVENTS LEADS US TO BELIEVE THERE MAY BE A SIGNAL RELATED PROB IN THE VICINITY OF RENCH INTXN. A PHONE DISCUSSION WITH A PVD TWR SUPVR INDICATED HIS TECHNICIANS WOULD LOOK INTO THE MATTER. IN THE MEANTIME; EXTRA CARE WILL BE EXERCISED ON THE ILS 5 PVD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR HAS TALKED TO HIS ACR SAFETY OFFICE WHICH HAS CONTACTED THE PVD FAA OPS PEOPLE. PVD COULD FIND NO PROB WITH THEIR NEWLY INSTALLED MK20 ILS SYS ON RWY 5. PVD HAS PASSED THIS INFO ON TO THE REGIONAL FAA FACILITIES PEOPLE. NO FEEDBACK HAS COME TO THE RPTR ON THIS YET. HIS ACR HAS PUT OUT A 'COMPANY NOTAM' WARNING CREWS THAT FLY INTO PVD TO BE ALERT TO THIS PROB. HAD THE RPTR NOT ACCIDENTALLY MET THE ACR B CAPT IN THE HOTEL LOBBY; HE PROBABLY WOULD HAVE DISMISSED HIS FULL SCALE DEFLECTION AT THE RENCH INTXN OM AS 'ONE OF THOSE THINGS.' PVD ATCT INDICATED THAT THERE WAS NO VEHICLE TFC NEAR THE LOC XMITTER DURING THE RPTR'S APCH.