FLT ASSIST TO GA PLT WHEN UNABLE TO TIE DOWN HIS HDGS TO INTERCEPT THE LOC ON AN IAP ILS APCH.

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WAS GONNA FLY AN AIRPLANE FROM BNA TO M02 (DICKSON). GOT UP XA20 AM TO CHK WX. WX LOOKED GOOD. WENT TO ARPT. ATIS RPTED 3300 SCATTERED; 15000 FT BROKEN. CALLED UP CLRNC; THEY SAID BNA WAS IFR. GOT SPECIAL VFR. IN THE CLB; ABOUT 1500 FT; CLOUDS WERE COMING IN FROM EVERYWHERE. FOUND A HOLE AND GOT OUT ON TOP BTWN LAYERS. TOLD CTLR THAT I WAS COMING BACK TO BNA AND REQUESTED LCL IFR CLRNC. APCH CTLR VECTORED ME AROUND FOR ILS TO RWY 2L. PUT IN THE FREQ; CHKED BEACONS; PUT MARKERS UP IN SPEAKER. CTLR HAD ME TURN L 050 DEGS; TO INTERCEPT ILS FOR RWY 2L. I HAD A R DEFLECTION OF THE LOC. APPROX 30 SECONDS LATER; CTLR TOLD ME I WENT THROUGH THE LOC; BUT I STILL HAD R DEFLECTION. THEY HAD ME TURN TO 350 DEGS AND THE LOC SLOWLY STARTED MOVING. I THOUGHT THAT NOW FINALLY THE LOC IS ALIVE. A MOMENT LATER THE CTLR TOLD ME I WENT THROUGH THE LOC AGAIN; THIS TIME TO THE L. MY NEEDLE WAS NOW TO THE L. NOW THEY TURNED ME TO 020 DEGS AND THE NEEDLE WAS CTRED. I THOUGHT I WAS TRACKING THE LOC NOW AND LOWER ASKED ME IF I GOT THE LOC. I REPLIED; I THINK I GOT IT NOW. WHEN I BROKE OUT; I WAS ON FINAL FOR RWY 2L. PROB: EQUIP MALFUNCTION WHEN FLOWN IN RAIN. PAX FLOOR SOAKED. TALKED TO A GUY ABOUT NAV FAILURE AND HE SAID THE SAME HAPPENED TO HIM IN THE SAME AIRPLANE WITH HIS INSTRUCTOR. THEY WERE FLYING IN RAIN AND IT QUIT; THEN WORKED; THEN QUIT. SO; REASON FOR BAD ILS PERFORMANCE IS DUE TO NAV FAILURE.