IMPROPER PLANNING/DECISION BY THE PILOT, HIS VFR FLIGHT INTO INSTRUMENT METEOROLOGICAL CONDITIONS (IMC), AND HIS LOSS OF AIRCRAFT CONTROL DUE TO SPATIAL DISORIENTATION. FACTORS RELATED THE ACCIDENT WERE: THE ADVERSE WEATHER CONDITIONS, HIGH TERRAIN, THE PILOT'S OVER CONFIDENCE IN HIS PERSONAL ABILITY, AND HIS LACK OF INSTRUMENT EXPERIENCE.