Narrative:

I was turned to intercept the localizer, told to 'maintain 3500 ft until established, cleared for the bur ILS 8 approach.' after intercepting the localizer, I watched as the GS needle came alive and at GS intercept extended the gear. I had the power set to 16 inches manifold pressure, 2500 FPM which configures the PA-32R with about a 500 FPM descent at 100 KTS. After a short time, I saw the GS needle was showing that I was slightly above glide path so I increased my rate of descent a bit with pitch and eased the power back somewhat to maintain 100 KTS. When I broke out of the overcast, I continued the approach flying the instrument's indications but soon realized that not all seemed right. I appeared visually to be low but all indications on the localizer and GS seemed normal. I leveled off to take stock of the situation and the controller notified me of an altitude alert. I advised him that I had just leveled off at 1900 ft and that I suspected I had a problem with my GS indicator. I was under the overcast at the time, so I maintained altitude and continued inbound until in a position to make a normal landing. Upon taxiing off the runway, I was asked to call the TRACON supervisor. He advised me that I had descended below the GS path. I told him I suspected I had a GS receiver/indicator problem and had descended below the glide path before realizing what the situation was. I went to the company's chief pilot to advise him of what had happened. I immediately wrote a maintenance report and took it to our in-house avionics shop. After analyzing the situation, I realize that it is easy to develop some complacency and rely on the normally very accurate ILS system. I missed several opportunities to catch that all was not normal and missed doing so by not using all the references and xchks available to me. The avionics department determined that the GS indicator was faulty and replaced the unit.

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Original NASA ASRS Text

Title: AN ATX SMA HAD AN ACFT EQUIP PROB FAULTY ILS INDICATOR.

Narrative: I WAS TURNED TO INTERCEPT THE LOC, TOLD TO 'MAINTAIN 3500 FT UNTIL ESTABLISHED, CLRED FOR THE BUR ILS 8 APCH.' AFTER INTERCEPTING THE LOC, I WATCHED AS THE GS NEEDLE CAME ALIVE AND AT GS INTERCEPT EXTENDED THE GEAR. I HAD THE PWR SET TO 16 INCHES MANIFOLD PRESSURE, 2500 FPM WHICH CONFIGURES THE PA-32R WITH ABOUT A 500 FPM DSCNT AT 100 KTS. AFTER A SHORT TIME, I SAW THE GS NEEDLE WAS SHOWING THAT I WAS SLIGHTLY ABOVE GLIDE PATH SO I INCREASED MY RATE OF DSCNT A BIT WITH PITCH AND EASED THE PWR BACK SOMEWHAT TO MAINTAIN 100 KTS. WHEN I BROKE OUT OF THE OVCST, I CONTINUED THE APCH FLYING THE INST'S INDICATIONS BUT SOON REALIZED THAT NOT ALL SEEMED RIGHT. I APPEARED VISUALLY TO BE LOW BUT ALL INDICATIONS ON THE LOC AND GS SEEMED NORMAL. I LEVELED OFF TO TAKE STOCK OF THE SIT AND THE CTLR NOTIFIED ME OF AN ALT ALERT. I ADVISED HIM THAT I HAD JUST LEVELED OFF AT 1900 FT AND THAT I SUSPECTED I HAD A PROB WITH MY GS INDICATOR. I WAS UNDER THE OVCST AT THE TIME, SO I MAINTAINED ALT AND CONTINUED INBOUND UNTIL IN A POS TO MAKE A NORMAL LNDG. UPON TAXIING OFF THE RWY, I WAS ASKED TO CALL THE TRACON SUPVR. HE ADVISED ME THAT I HAD DSNDED BELOW THE GS PATH. I TOLD HIM I SUSPECTED I HAD A GS RECEIVER/INDICATOR PROB AND HAD DSNDED BELOW THE GLIDE PATH BEFORE REALIZING WHAT THE SIT WAS. I WENT TO THE COMPANY'S CHIEF PLT TO ADVISE HIM OF WHAT HAD HAPPENED. I IMMEDIATELY WROTE A MAINT RPT AND TOOK IT TO OUR IN-HOUSE AVIONICS SHOP. AFTER ANALYZING THE SIT, I REALIZE THAT IT IS EASY TO DEVELOP SOME COMPLACENCY AND RELY ON THE NORMALLY VERY ACCURATE ILS SYS. I MISSED SEVERAL OPPORTUNITIES TO CATCH THAT ALL WAS NOT NORMAL AND MISSED DOING SO BY NOT USING ALL THE REFS AND XCHKS AVAILABLE TO ME. THE AVIONICS DEPT DETERMINED THAT THE GS INDICATOR WAS FAULTY AND REPLACED THE UNIT.

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.