PLT OF AN SMA SEL EXECUTED A MISSED APCH WHEN DISCOVERING THAT HIS ILS GS INDICATOR WAS GIVING A FALSE READING.

Narrative

BEGAN A NORMAL ILS APCH TO CLM IN IMC. ILS RECEIVER CONSISTS OF A BENDIX/KING KX155 750 RECEIVER WITH A KI- 209 INDICATOR. THE FLAGS ON THE INDICATOR WERE BOTH SHOWING 'VALID' AND USABLE SIGNALS. A 500 FPM DSCNT WAS INITIATED OVER THE OM; THE GS NEEDLE WAS CTRED AS WAS THE LOC NEEDLE. UPON ESTABLISHING VISUAL CONTACT WITH THE ARPT AT APPROX 2000 FT AGL; I REALIZED THE APCH WAS ABNORMALLY HIGH AND THAT THE GS NEEDLE HAD NEVER DEVIATED FROM JUST SLIGHTLY OFF CTR EVEN THOUGH THE GS FLAG INDICATED NORMAL. I IMMEDIATELY INITIATED A MISSED APCH AS A SAFE LNDG FROM THAT ALT WAS NOT POSSIBLE; WHEREUPON I RETURNED TO MY STARTING ARPT (PAE) AND COMPLETED AN UNEVENTFUL LOC ONLY APCH. HAD THE CEILINGS AT CLM BEEN LOWER; I MIGHT NOT HAVE RECOGNIZED THE INST FAILURE UNTIL MUCH LATER; POSSIBLY HAVING IMPACTED TERRAIN OR OBSTACLES. AT THE TIME OF THE INCIDENT I WAS NOT IN CONTACT WITH THE APCH CTLR; HAVING SWITCHED TO THE CTAF FREQ. I WOULD RECOMMEND THAT SUCH INSTS BE REQUIRED TO 'FAIL' TO A MORE OBVIOUS OFF COURSE INDICATION; AS OPPOSED TO FAILING TO A CTRED POS; AS IN THIS INST. THIS WOULD HAVE TIPPED ME OFF AT THE BEGINNING OF THE APCH AS OPPOSED TO MOST OF THE WAY THROUGH IT. IN THE END THE PROB WAS DIAGNOSED AS MERELY AN INTERMITTENT WIRE.