AN ACR FREIGHTER MLG CREW HAD A LOW ALT ALERT ON AN ILS APCH.

Narrative

WHILE BEING VECTORED FOR THE ILS RWY 17 APCH AT PNS; BOTH NAV RECEIVERS WERE TUNED AND IDENTED BY MYSELF. LOC INTERCEPT OCCURRED NORMALLY WITH A FULL 'FLY UP' GS INDICATION ON BOTH GS INDICATORS. ESTABLISHED ON THE LOC; BOTH GS INDICATORS CAME 'ALIVE' AND THE ACFT WAS SUBSEQUENTLY CONFIGURED AS PER NORMAL PROC. THE GLIDEPATH WAS INTERCEPTED AND FOLLOWED NORMALLY. AT APPROX 500 FT AGL; THE APCH CTLR ANNOUNCED A 'LOW ALT ALERT' AND A MISSED APCH WAS INITIATED IMMEDIATELY. THE CTLR STATED OUR POS AS APPROX 'BRENT' ON THE FINAL APCH COURSE. WE SUBSEQUENTLY CLBED BACK UP TO OUR VECTORING ALT. I ASKED THEM TO CHK THEIR EQUIP AND; AT THE SAME TIME; CYCLED MY NAV RECEIVER AND RETUNED AND IDENTED MY ILS FREQ. MY INDICATOR #2 SUBSEQUENTLY APPEARED NORMAL AND THE #1 GS INDICATED ERRONEOUSLY (I.E; ON GS WITH NON FLAGS) FOR OUR POS (XWIND IN THE RADAR PATTERN). THE FOLLOWING APCH WAS FLOWN AFTER ASSESSING MY INDICATORS AS FUNCTIONAL; WITHOUT INCIDENT. THE #1 NAV REMAINED INCORRECT (ON GS/NO FLAGS) THROUGHOUT THE APCH. AS FOR CONTRIBUTING FACTORS; I CITE MAINLY EQUIP FAILURE; I.E.; INCORRECT GS INDICATIONS AND #1 AND #2 NAV INDICATORS.