THE PILOT'S LOSS OF AIRCRAFT CONTROL DUE TO SPATIAL DISORIENTATION AFTER CONTINUING THE VFR FLIGHT INTO INSTRUMENT METEOROLOGICAL CONDITIONS. FACTORS RELATING TO THE ACCIDENT WERE: THE EXISTING WEATHER CONDITIONS AND DARK NIGHT THAT CONTRIBUTED TO THE PILOT'S SPATIAL DISORIENTATION, THE FAILURE OF THE FSS WEATHER OBSERVER TO INFORM THE IN-FLIGHT SPECIALIST AND CENTER CONTROLLER THAT THE AIRPORT WAS UNDER IFR CONDITIONS, AND THE FAILURE OF THE FSS RELIEF IN-FLIGHT SPECIALIST TO MAKE HIMSELF AWARE OF THE CURRENT OFFICIAL WEATHER OBSERVATIONS AND TO THEN INFORM THE PILOT.