ACFT EQUIP PROB. FALSE GS. RPTR PLT FOLLOWED FALSE GS UNTIL TWR WARNED HIM OF LOW ALT AT WHICH TIME HE DID A GAR. RPTR ATTRIBUTES PART OF PROB TO FATIGUE.

Narrative

I WAS ON AN IFR FLT PLAN IN IMC WHILE CONDUCTING THE ILS RWY 24 APCH INTO ISP. THE APCH CLRNC WAS TO FOLLOW THE CCC TRANSITION AND TO MAINTAIN 5000 FT UNTIL CCC. THE APCH PROC; AS PUBLISHED; THEN ALLOWS DSCNT TO 2000 FT AFTER CCC VOR. DURING THE TRANSITION SEGMENT FROM CCC TO JOIN THE LOC; I TUNED AND IDENTED RADIOS FOR THE APCH. THIS INCLUDED TURNING ON AUDIO AND VERIFYING OP OF MARKER BEACON LIGHTS. WHILE INTERCEPTING THE LOC; THE GS FLAG DISAPPEARED FROM THE #1 NAV INDICATOR AND DISPLAYED THE AIRPLANE AS BEING APPROX 1 1/2 DOTS 'HIGH' ON THE APCH. THIS INDICATION APPEARED PROPER TO ME AT THE TIME GIVEN MY UNUSUALLY HIGH ALT ON THIS SEGMENT OF THE APCH. I THEREFORE CONTINUED TRACKING THE GS UNDER THIS CONDITION. I SOON FOUND MYSELF IN A SIT WHERE I WAS PARALLELING THE GS RATHER THAN INTERCEPTING IT; WITH AN EXCESSIVE DSCNT RATE. I ATTRIBUTED THE HIGH DSCNT RATE TO MY FAST AIRSPD OF 150 KIAS WHICH I WAS TOLD TO MAINTAIN TO THE MARKER BECAUSE OF FASTER FOLLOWING TFC. APCH SHORTLY SWITCHED ME TO TWR. UPON CONTACTING TWR; THEY SOON NOTIFIED ME OF A 'LOW ALT' ALERT AND ADVISED I WAS TOO LOW FOR THIS SEGMENT OF THE APCH. THEY FURTHER SAID I WAS OUTSIDE THE MARKER AND MY ALT WAS 900 FT AND FURTHER ASKED TO STATE MY INTENTIONS. I ADVISED TWR I WAS GOING MISSED. DURING THIS APCH; I WAS FOLLOWING A FALSE INDICATION OF THE GS (IT WAS STUCK IN THIS INDICATION!) AND LOST TRACK OF MY POS DURING THE APCH WHICH ALLOWED THIS UNSAFE DSCNT BELOW THE PUBLISHED MINIMUM ALTS. I WAS ALSO THINKING ABOUT CHKING MY ALT AT THE MARKER TO ENSURE PROPER INTERCEPT ALT WAS ATTAINED; BUT I FAILED TO DO SO BECAUSE OF BEING ENGROSSED IN FOLLOWING THE ERRONEOUS INST INDICATIONS. CONTRIBUTING FACTORS: I CONSIDER UNSAFE FACTORS DURING THIS APCH AS BEING NUMEROUS. SOME OF WHICH AS FOLLOWS: LONG DUTY DAY OF 13 HRS AND UP T THIS POINT HAVING FLOW 6.9 HRS BEING A SINGLE PLT OP. THIS DAY ENTAILED 6 ILS APCH PRIOR TO THIS INCIDENT AND APPROX 5.5 HRS IN ACTUAL IMC WITH WIDESPREAD TSTM ACTIVITY AND LOW ILS APCHS BEING CONDUCTED TO ALMOST ALL ARPTS I WAS USING DURING THIS DAY. THIS LEADS TO FATIGUE AND COMPLACENCY. HAVING CONDUCTED NUMEROUS APCHS DURING THIS POOR WX DAY; I FOUND MYSELF NOT GIVING THE APCH THE ATTN IT DESERVES. I SHOULD HAVE HAD A MUCH BETTER INST SCAN GOING AS WELL AS A SHARPER PICTURE ON MY POS DURING THE ENTIRE APCH SEGMENT; INCLUDING DOUBLE-CHKING MY ALT AT THE OM. THE FALSE GS INDICATOR FURTHER LULLED ME INTO COMPLACENCY. APCH REQUESTED I KEEP A FASTER THAN NORMAL APCH SPD. I WAS CONCERNED ABOUT PLEASING THEM AND THE MUCH FASTER JET ACFT FOLLOWING ME TO THE FIELD.