CAPT OF AN MD88 DSNDED BELOW PUBLISHED APCH ALT DURING AN ILS APCH RESULTING IN TWR CTLR ISSUING A LOW ALT ALERT.

Narrative

WE WERE CLRED FOR THE ILS RWY 3; GS OTS. I HAD THE ILS FREQ IN MY NAV RADIO AND THE FO INITIALLY HAD SPA VOR FREQ IN HIS NAV RADIO. GREER IAF FREQ 287 WAS SET IN THE ADF. RAW DATA ON THE LOC WAS MONITORED AND CONFIRMED FOR THE LOC INTERCEPT. THE MAP DISPLAY APPEARED TO BE ACCURATE AS I WENT BACK TO MAP ON MY NAV DISPLAY. THE FO MONITORED RAW DATA (ILS FREQ RWY 3) ON HIS NAV DISPLAY. THE MAP DISPLAY ON MY NAV DISPLAY SHOWED THAT WE WERE PASSED THE IAF AND THE ADF NEEDLE BOUNCED A FEW TIMES. I (PF) DECIDED TO DSND DUE TO THE FACT THAT WE HAD THE GND IN SIGHT AND THE FORWARD VISIBILITY WAS SUCH (ESTIMATED 4-5 MI) THAT THE AIRFIELD ENVIRONMENT (NO TREES) APPEARED TO BE IN SIGHT. (APCH LIGHTS WERE OTS.) THE FO WAS UNSURE THAT WE HAD PASSED THE ADF BUT I THOUGHT WE HAD BASED UPON THE FACT THAT THE IAF ON THE MAP DISPLAY WAS NOW WELL BEHIND US AND I HAD SEEN THE ADF NEEDLE MOVING. WE WERE DSNDING AT 1500 FPM WHEN WE GOT A CALL FROM THE TWR THAT THE TWR HAD A LOW ALT ALERT. WE CONFIRMED WE HAD THE GND IN SIGHT. REALIZING WE WERE NOT WHERE I THOUGHT WE WERE. I STOPPED THE DSCNT AND DROVE IN TOWARD THE FIELD AT APPROX 2000 FT MSL. ALTHOUGH WE WOULD NOT HAVE DSNDED IN IMC WITHOUT A MORE POSITIVE IDENT ON THE IAF (IE; RADAR FIX); WITH THE ADF NEEDLE LOCKING AND UNLOCKING; THE FACT IS THAT THIS WAS CONFUSING DUE TO THE LACK OF DME AND A MAP DISPLAY THAT APPEARED TO BE CORRECT BUT WAS OBVIOUSLY NOT.