CORPORATE H25C PIC RPT REGARDING OSCILLATIONS OF THE LOC COURSE ON ILS APCH FOR RWY 12R AT STL.

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THE ILS LOC TO RWY 12R AT STL IS VERY ERRATIC. THIS HAS BEEN THE CASE FOR AT LEAST 15 YRS. ALL RPTS TO THE CTL TWR ARE NOTED BUT THE LOC REMAINS VERY ERRATIC JUMPING FROM SIDE TO SIDE. CLRED FOR ILS RWY 12R. WX 11000 FT 5 MI IN MIST. ILS IDENT CLR AND STRONG. NEEDLE AS ALWAYS SWINGS ERRATICALLY FROM SIDE TO SIDE. USE OF FLT DIRECTOR IN NAV MODE IS IMPOSSIBLE. WE BROKE OUT RIGHT OF CTRLINE IN THE AREA OF NEW UNOPENED RWY. VISUALLY ACQUIRED RWY AND COMPLETED APCH AFTER BEING CLRED FOR A VISUAL APCH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE PIC STATED THAT HE HAS OBSERVED THIS EXTREME OSCILLATING OF THE LOCALIZER AS A PROB FOR SOME TIME AND HAS RPTED IT VERBALLY TO LCL AND GND CTLRS AT STL. HE FURTHER STATED THAT HE SOMETIMES 'GETS IT BACK' INSIDE THE LOM. ON THIS OCCASION; WHEN CHANGING TO LCL CTLR; HE HEARD HALF OF A CONVERSATION WHERE THE PREVIOUS FLT WAS RPTING THE SAME PROB TO THE TWR. THE CTLR RESPONDED WITH A; 'IT MONITORS OK.' RPTR TOLD LCL AND GND OF HIS PROB AS WELL. RPTR INTENDS TO HAVE THE CORPORATION PLACE A NOTICE IN A RPTING SOURCE REGARDING THIS RWY 12R LOCALIZER PROB.