SMT X NON ADHERENCE TO APCH PROC FLEW THROUGH LOC. POSSIBLE UNRELIABLE LOC.

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SMT X (BE-90) WAS CLRED BY ME FOR ILS/DME RWY 21 APCH TO FLG AFTER HOLDING FOR ALMOST 50 MIN (TO AWAIT THE OPENING OF FLG AFTER SNOW REMOVAL). SMT X REACHED FRISY AND COMMENCED THE APCH. HE CONTINUED NWBOUND PAST THE INBOUND RADIAL AND JUST AS I WAS ABOUT TO QUESTION SMT X; I NOTICED HE HAD TURNED S. AT THAT TIME; I ASKED THE PLT HIS HDG AND HE ANSWERED '170.' HE THEN INTERCEPTED THE LOC AND PROCEEDED INBOUND. THE REASON FOR THIS FORM IS MY CONCERN OVER THE POSSIBLE UNRELIABILITY OF THE FLG ILS/DME APCH. OVER THE LAST FEW WEEKS THERE HAVE BEEN A NUMBER OF OCCURRENCES INVOLVING THIS APCH THAT HAVE CAUSED GREAT CONCERN AMONG THE CTLRS IN THIS SPECIALTY. GRANTED; SOME OF THESE HAVE BEEN TRACED BACK TO PLT ERROR AND INST MALFUNCTION; BUT WE CANNOT BELIEVE ALL OF THESE INCIDENTS ARE ATTRIBUTABLE TO THOSE. THERE WAS ALSO A BE- 02 WHO WAS CLRED FOR THE ILS/DME AND GOT A FULL NEEDLE DEFLECTION ON THE GS AND SUBSEQUENTLY A RED FLAG; AND; AS I UNDERSTAND; ENDED UP GOING BACK TO PHX TO LAND. I BELIEVE THERE IS A PROB WITH THE ILS APCH AT FLG AND SOMETHING MORE INVOLVED THAN JUST A MERE FAA FLT CHK NEEDS TO BE DONE THERE.