A C182 ON AN ILS APCH TO VNY DSNDED BELOW GS ALTS WHILE FLYING THE APCH WITH A STUCK GS INDICATOR. VNY TWR NOTED THE DISCREPANCY AND WAS INSTRUMENTAL IN THE PLT GOING AROUND.

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ON IFR FLT TO VNY I HAD RECEIVED MY FINAL VECTOR FOR THE ILS RWY 16R TO VNY. THE LOC WAS IDENTED AND BOTH LOC AND GS NEEDLES WERE ALIVE -- NO FLAGS; AND RECEIVING PROPER IDENT. DME WAS GIVING DISTANCE READOUT TO VNY. THE LOC AND GS BOTH CAPTURED AND I BEGAN MY DSCNT ON GS. RATE OF DSCNT WAS APPROX 850 FPM; SPD 120 KTS. AT THIS POINT; I WAS INSTRUCTED BY SOCAL APCH TO CONTACT VNY TWR. I MADE INITIAL CALL TO TWR; CONTINUING THE APCH. NEEDLES BOTH CTRED. AFTER XING THE OM; I RECEIVED A LOW ALT ALERT CALL FROM TWR TO CHK ALT IMMEDIATELY. AGAIN BOTH NEEDLES WERE CTRED WITH NO FLAGS. I LOOKED AT MY ALTIMETER THEN BACK TO THE GS AND AT FIRST GLANCE EVERYTHING SEEMED NORMAL. TWR THEN CALLED AGAIN AND ASKED IF THE ARPT WAS IN SIGHT. I SAID NO. THEY THEN ASKED WAS MY GS WORKING. I SAID YES; THEN RECEIVED ANOTHER ALT ALERT. AT THIS POINT I LEVELED OFF AND STOPPED THE DSCNT. THERE WAS NO CHANGE ON GS INDICATION. TWR AGAIN ASKED IF MY GS WAS WORKING. I REPLIED; I AM HAVING PROBS WITH THE GS AND IT MAY BE INOP. TWR REPLIED; STATE INTENTIONS; WHICH I REPLIED; I AM GOING MISSED APCH. TWR GAVE ME A HDG AND ALT AND I WAS HANDED OFF TO SOCAL APCH. APCH ASKED ME WHAT I WOULD LIKE TO DO. I TOLD THEM I WOULD LIKE THE VOR APCH INTO VNY. THEY WERE VERY HELPFUL AND GAVE ME RADAR VECTORS FOR THE VOR APCH. I FLEW THE APCH; CONTACTED VNY TWR AND LANDED. THE ACFT WAS BEING FLOWN TO VNY FOR UHF RADIO MAINT. I EXPLAINED WHAT HAD HAPPENED TO THE AVIONICS MECH. THE MECH/TECHNICIAN INFORMED ME AFTER TESTING THE NAV RADIOS; THAT INDEED I WAS RECEIVING THE ILS SIGNAL. HENCE; THAT IS WHY THERE WERE NO FLAGS ON MY GS. HOWEVER; THE GS NEEDLE 'FROZE' AT THE CTR POS; GIVING ME A FALSE INDICATION OF BEING RIGHT ON GS. HENCE; EXPLAINING MY LOW ALT. GS'S ARE GREAT INSTS. HOWEVER; LIKE EVERYTHING ELSE; THEY ARE SUBJECT TO BREAK OR BECOME INOP. IN HINDSIGHT; I SHOULD HAVE REALIZED THIS SOONER BY NOTING MY DISTANCE AND ALT FROM THE ARPT. LOW ALT ALERTS ARE THERE FOR A REASON AND I AM GRATEFUL. AGAIN I SHOULD HAVE BEEN QUICKER TO REALIZE SOMETHING WAS AMISS. AFTER EXECUTING THE MISSED APCH AND FLYING THE VOR APCH TO LAND; I FELT THAT FILLING OUT THIS RPT WOULD BE A HELP IF I COULD SHARE THIS WITH OTHERS. THE GS WAS REPAIRED THAT VERY DAY AND I FLEW HOME TO MYF IFR TO AN ILS APCH AND LNDG. ONLY THIS TIME PAYING MUCH MORE ATTN TO MY ALT!