A CRJ200 ATTEMPTED A COUPLED ILS ON PIT RWY 28R. UNANNOUNCED LOC TRANSMITTER MAINT PREVENTED LOC CAPTURE. A GAR WAS INITIATED FOLLOWED BY A VISUAL APCH.

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WE WERE CLRED TO LAND ON A VISUAL APCH TO RWY 28R AT PIT BOTH PLTS WERE IN GREEN DATA WITH THE LOC TO RWY 28R SELECTED; IDENTED AND VERIFIED WE WERE ON A R DOGLEG TO INTERCEPT THE FINAL APCH COURSE. APCH MODE WAS ANNUNCIATED; BUT THE AUTOPLT DID NOT CAPTURE THE LOC. THE CAPT AND I BOTH NOTICED THIS. I TOOK THE AIRPLANE OFF AUTOPLT AND TURNED TOWARD RWY 28R MANUALLY. AS I DID THIS; THE GPWS GAVE A TERRAIN WARNING. WE DECIDED TO GO AROUND. I INITIATED THE GAR AND THE CAPT CALLED THE TWR. A SECOND OR TWO LATER; THE TWR CALLED AND ASKED OUR INTENTIONS. THE CAPT REPEATED THE GAR CALL. THE TWR CALLED AGAIN ASKING OUR INTENTIONS. IT APPEARED THAT THEY DID NOT HEAR OUR CALLS. FINALLY ON THE 3RD XMISSION; THE TWR ACKNOWLEDGED THE GAR AND GAVE INSTRUCTIONS TO STAY IN THE PATTERN FOR ANOTHER VISUAL TO RWY 28R AND CLRED US TO LAND. WE ATTEMPTED TO ENGAGE THE AUTOPLT FOR THIS APCH TOO; BUT IT WOULD NOT CAPTURE ALT OR THE LOC. I THEN CONTINUED TO HAND FLY THE AIRPLANE AND LAND ON RWY 28R. THE CAPT CALLED THE TWR SUPVR AFTER WE LANDED. ACCORDING TO THE CAPT; THE SUPVR SAID THAT THE LOC FOR RWY 28R WAS 'BEING WORKED ON' AND WAS DIRECTED 'THE OTHER WAY.' THE CAPT AND I BOTH LISTENED TO ATIS BEFORE THE APCHS AND THERE WAS NO MENTION OF THIS MAINT ACTION. NOTE: WHEN THE GPWS GAVE THE TERRAIN WARNING; WE WERE AT ABOUT 3000 FT MSL AND ABOUT 2000 FT AGL. THE CAPT CALLED MAINT AND WAS ADVISED TO COMPLETELY PWR DOWN THE AIRPLANE AND REBOOT THE AVIONICS. AFTER HE DID THIS WE RETURNED TO JFK. SUPPLEMENTAL INFO FROM ACN 748712: THE SUPVR SAID THAT SINCE THE 'VISUAL APCH WAS IN' THERE WAS NO GUARANTEE THAT THE LOC AND GS WOULD WORK. HE SAID HE JUST WANTED TO KNOW WHY WE WENT AROUND AND THERE WAS NO PROB.