WHILE ENROUTE IN THE COMPANY OF ANOTHER AIRCRAFT, CLOUDS WERE ENCOUNTERED. THE AIRCRAFT CONTINUED VFR INTO IMC CONDITIONS. SUBSEQUENTLY DEPARTURE FROM CONTROLLED FLIGHT OCCURRED AND ALTITUDE WAS NOT MAINTAINED. THE AIRCRAFT IMPACTED TREES AND THE TERRAIN IN A REMOTE AREA. THE ACCIDENT OCCURRED ON AUGUST 1, 1981. THE AIRCRAFT WAS LOCATED ON NOVEMBER 5, 1990.