DRG ARRIVAL, THE PLT WAS ADVISED THE DESTN WX WAS: ESTD 500' OVERCAST, VIS 1 MI WITH FOG, ARPT BLO MINS. THE PLT ELECTEDTO MAKE AN NDB RWY 23 APCH, BUT SAID HE WOULD DIVERT IF A MISSED APCH WAS MADE. HE WAS PROVIDED RADAR VECTORS & WAS CLRDFOR THE APCH. AT THE IAF (INITIAL APCH FIX/TINEY INTXN), RADAR SVC WAS TERMINATED & THE PLT WAS TOLD TO CONTACT TWR. ON TWR FREQ, THE PLT WAS AGAIN REMINDED THE ARPT WAS BLO MINS. APRX 2 MIN LATER, HE RPRTD OVR THE OUTER MARKER (OM) WHICH WAS 4.2 MI PAST (SW OF) THE NDB/FINAL APCH FIX (FAF) & 3.9 MI NE OF THE ARPT. SECONDS LATER, THE TWR X-MITTED INFO (JUSTRECD FM ARTCC) THAT THE ACFT WAS 2-1/2 MI EAST OF COURSE. TWR TRIED TO NOTIFY THE PLT, BUT RADIO & RADAR CONTACT WERE LOST. INV REVEALED THE ACFT IMPACTED A RIDGE NRLY 4 MI PAST THE NDB & 2 MI LEFT OF COURSE AT AN ELEV OF APRX 1900', BUT BFR PASSING THE OM. MIN DSCNT ALT (MDA) BTN THE NDB & OM WAS 2220' MSL. MDA AFTER PASSING THE 0M WAS 1940'; ARPT ELEV WAS 1161'. NO PREIMPACT ACFT PROBLEMS WERE FND. THE NDB FACILITY OPERATED SAFTISFACTORILY DURING FLT & GROUND CHECKS.