SMA ON LOC APCH BEGINS DSCNT TO MDA PRIOR TO PASSAGE OF FINAL APCH FIX.

Narrative

I WAS INBOUND ON THE ILS 17L; OUTSIDE THE OM (LEROI). THE PROB CAME ABOUT WHEN THE ADF NEEDLE SWING TO THE FROM INDICATION. THE PROB WAS DISCOVERED WHEN I WAS DSNDING TO THE MDA OF 860 MSL; WHEN I WAS AT ABOUT 1400 MSL. I IMMEDIATELY STARTED A CLB BACK TO 2300 MSL. THE CONTRIBUTING FACTORS TO THIS WERE IMPROPER XCHK OF LEROI USING THE 055 RADIAL OF WACO VOR; ALSO NOT RECEIVING AN ORAL OR MARKER BEACON LIGHT OR WAITING FOR THE GS TO COME IN. THE REASON I LEFT THE ALT OF 2300 MSL WAS THE GS FLAG WAS GOING ON AND OFF; SO I DECIDED TO DO A LOC TO RWY 17L INSTEAD OF THE ILS. ALSO; THE ADF NEEDLE SWING TO THE FROM POS SO I THOUGHT I HAD CROSSED THE STATION (LEROI) INBOUND. I KNOW NOW NOT TO USE JUST ONE SOURCE OF INFO TO IDENT THE FINAL APCH FIX. I KNOW THAT STATIONS OF LOW PWR DO NOT ALWAYS GIVE THE MOST ACCURATE INDICATIONS. SO THE BEST THING TO DO IN THAT SIT WOULD BE TO WAIT FOR THE GS TO COME IN AND THE ORAL AND VISUAL INDICATIONS OF THE MARKER BEACON; THEN USE THE SWING OF THE NEEDLE ON THE ADF TO CONFIRM PASSAGE OF THE STATION.