AFTER TRANSPORTING PASSENGERS FROM LONGVIEW, TX TO OKLAHOMA CITY, OK & RETURN TO LONGVIEW, THE ACFT WAS REFUELED FOR A FLT BACK TO NACOGDOCHES, TX, WHERE THE ACFT WAS BASED. ABOUT 12 MIN AFTER TAKEOFF, THE PLT WAS CLEARED FOR AN NDB APCH TO NACOGDOCHES & INSTRUCTED TO CONTACT THE LUFKIN FSS FOR WX & CURRENT ALTIMETER SETTING. DURING THE NDB APCH, THE ACFT COLLIDED WITH TREES, CRASHED & BURNED. AN INVESTIGATION REVEALED NO EVIDENCE OF EITHER AN ENG OR AIRFRAME FAILURE OR MALFUNCTION. INITIAL IMPACT OCCURRED WITH TREES ABOUT 700 YDS EAST OF THE NDB SITE. INITIALLY, TREES WERE CUT IN AN UPSLOPING MANNER WHERE THE TERRAIN SLOPED UPWARDS. ELEVATION OF THE CRASH SITE WAS 530 FT MSL. THE MIN DESCENT ALT (MDA) WAS 900 FT MSL. ABOUT 28 MI NORTH, THE 1955 CDT WX AT LUFKIN WAS, IN PART: 3500 FT BROKEN, VISIBILITY 5 MI. HOWEVER, WITNESSES AT NACOGDOCHES REPORTED CONSIDERABLY LOWER CEILINGS, REDUCED VISIBILITY & SOME HILLTOPS OBSCURED BY CLOUDS. A PLT WITNESS REPORTED LIGHT RAIN, FOG IN THE TREETOPS. REPORTEDLY, THE ARPT WAS BELOW MINS