DRG ARRIVAL, THE PLT REPORTED A PROBLEM WITH HIS #1 NAV, BUT SAID HE WOULD TRY TO MAKE AN ILS APCH. HE SAID HE WOULD RETURN TO PONTIAC, IF HIS ILS DID NOT WORK. ARTCC CLEARED HIM FOR THE ILS RWY 32 APCH & INSTRUCTED HIM TO CONTACT PELLSTON RADIO (FSS). AT 1525, HE CALLED THE FSS & REPORTED HE WAS 20 MI SOUTH. AT APRX 1534, THE FSS SPECIALIST HEARD AN ACFT FLY OVER, BUT DID NOT KNOW IF IT WAS N24RT. HE ASKED THE PLT IF HE WAS MAKING A MISSED APCH. THE PLT GAVE A NEGATIVE REPLY & REPORTED HE WAS PICKING UP THE GLIDE SLOPE, THEN SAID HE WAS HAVING TROUBLE WITH HIS #1 NAV. A WITNESS ABOUT 6 MI NORTH & WEST OF THE ARPT SAW THE ACFT ON A NORTHERLY HEADING AT ABOUT 200 FT AGL. ABOUT 1 MIN LATER, THE ACFT COLLIDED WITH TREES, CRASHED & BURNED APRX 8 MI FROM THE ARPT AT AN APRX ELEV OF 900 FT. THE ARPT ELEV WAS 720 FT. THE NAV EQUIPMENT WAS TOO BADLY DAMAGED DRG THE ACDNT TO BE TESTED. ACCORDING TO THE ACFT RADIO LOG, THE LAST VOR CHECK WAS ON 9/10/83. THE PLT HAD LOGGED 5.4 HRS OF INSTRUMENT TIME DRG THE PREV 6 MOS, BUT HAD NOT LOGGED ANY APCHS.