Narrative:

I was on an IFR flight plan in IMC while conducting the ILS runway 24 approach into isp. The approach clearance was to follow the CCC transition and to maintain 5000 ft until CCC. The approach procedure, as published, then allows descent to 2000 ft after CCC VOR. During the transition segment from CCC to join the localizer, I tuned and idented radios for the approach. This included turning on audio and verifying operation of marker beacon lights. While intercepting the localizer, the GS flag disappeared from the #1 navigation indicator and displayed the airplane as being approximately 1 1/2 dots 'high' on the approach. This indication appeared proper to me at the time given my unusually high altitude on this segment of the approach. I therefore continued tracking the GS under this condition. I soon found myself in a situation where I was paralleling the GS rather than intercepting it, with an excessive descent rate. I attributed the high descent rate to my fast airspeed of 150 KIAS which I was told to maintain to the marker because of faster following traffic. Approach shortly switched me to tower. Upon contacting tower, they soon notified me of a 'low altitude' alert and advised I was too low for this segment of the approach. They further said I was outside the marker and my altitude was 900 ft and further asked to state my intentions. I advised tower I was going missed. During this approach, I was following a false indication of the GS (it was stuck in this indication!) and lost track of my position during the approach which allowed this unsafe descent below the published minimum altitudes. I was also thinking about checking my altitude at the marker to ensure proper intercept altitude was attained, but I failed to do so because of being engrossed in following the erroneous instrument indications. Contributing factors: I consider unsafe factors during this approach as being numerous. Some of which as follows: long duty day of 13 hours and up T this point having flow 6.9 hours being a single pilot operation. This day entailed 6 ILS approach prior to this incident and approximately 5.5 hours in actual IMC with widespread thunderstorm activity and low ILS approachs being conducted to almost all airports I was using during this day. This leads to fatigue and complacency. Having conducted numerous approachs during this poor WX day, I found myself not giving the approach the attention it deserves. I should have had a much better instrument scan going as well as a sharper picture on my position during the entire approach segment, including double-checking my altitude at the OM. The false GS indicator further lulled me into complacency. Approach requested I keep a faster than normal approach speed. I was concerned about pleasing them and the much faster jet aircraft following me to the field.

Google
 

Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.