THE PILOT'S FAILURE TO MAINTAIN CONTROL OF THE AIRCRAFT AFTER BECOMING SPATIALLY DISORIENTED, AND HIS EXCEEDING THE DESIGN STRESS LIMITS OF THE AIRCRAFT WHILE ATTEMPTING TO RECOVER FROM AN UNCONTROLLED DESCENT. FACTORS RELATED TO THE ACCIDENT WERE: DARKNESS, CLOUD CONDITION, PILOT FATIGUE, AND THE PILOT'S LACK OF INSTRUMENT EXPERIENCE. .