PLT OF AN SMA SEL ACFT DSNDED BELOW APCH OM MINIMUMS AFTER FOLLOWING AN ERRONEOUS GS INDICATION.

Narrative

DSCNT BELOW MINIMUMS WHILE ON ILS INST APCH IN IMC. HAD INTERCEPTED LOC. APCH HAD ADVISED ME TO TELL TWR WHEN I WAS LOM INBOUND. I HAD THE VOR/DME; ADF AND MARKER BEACON INDICATORS SET UP TO TELL ME WHEN I REACHED THE LOM. THE GS STARTED GOING DOWN RAPIDLY. I ADVISED TWR 'OM INBOUND' AND BEGAN TO DSND TO CATCH THE GS. AFTER A WHILE; I DSNDED SLIGHTLY BELOW THE GS. I ADDED PWR. I BELIEVE THAT I MAY HAVE DSNDED ALMOST 1000 FT BELOW MDA. I CONTINUED TO ADD PWR. I NOTICED THAT MY DSCNT HAD STOPPED. I STARTED TO CLB. THE ADF NEEDLE WAS POINTING STRAIGHT AHEAD. I CONTINUED TO CLB UNTIL I WAS BACK UP TO THE MDA. I WAS CONCERNED AND CONFUSED UNTIL I SAW THAT THE DME INDICATED THAT I HAD NOT REACHED THE LOM. I CONTINUED TO THE LOM; MADE THE APCH AND LANDED. AS BEST I CAN TELL; I MUST HAVE GOTTEN A FALSE SIGNAL ON THE GS AND IN MY RUSH TO CHASE IT DOWN; I FORGOT TO NOTICE THAT THE MARKER BEACON INDICATORS NEVER WENT OFF. (IN SOME CASES IT IS NORMAL TO BEGIN YOUR DSCNT BEFORE REACHING THE LOM; BUT NOT ON THIS PARTICULAR APCH.) THIS WAS MY FIRST SOLO INST APCH TO MINIMUMS. I HAD BEEN IN THE ACFT FOR OVER 5 HRS. LESSON LEARNED: DON'T TRUST THE GS -- USE YOUR XCHKS.