VFR FLIGHT BY THE PILOT INTO INSTRUMENT METEOROLOGICAL CONDITIONS, HIS FAILURE TO MAINTAIN CONTROL OF THE AIRPLANE DUE TO SPATIAL DISORIENTATION, AND THE PILOT ALLOWING THE DESIGN STRESS LIMITS OF THE AIRCRAFT TO BE EXCEEDED. FACTORS RELATED TO THE ACCIDENT WERE FAILURE OF THE PILOT TO OBTAIN A PREFLIGHT WEATHER BRIEFING, DARKNESS, AND THE ADVERSE WEATHER CONDIITON.