The airplane was destroyed when it departed from cruise flight at 0920 Eastern time and impacted terrain. The Commercial pilot and three passengers received fatal injuries. The flight departed Sheboygan, Wis., at 0738 and was en route to Lebanon, Ohio. Ground fog was present in the area of the accident site; however, the airplane was in visual conditions on an IFR flight plan at its cruise altitude. Radar track data indicate that, at 0919:42, the airplane was on a heading of 135 degrees at 7000 feet msl. At 1419:47, radar data indicate the airplane at 6900 feet msl, and descending. At 1420:02, the airplane was at 3400 feet msl. No further radar contact with the airplane was recorded. At 0920, the surface weather observation at Benton Harbor, Mich., about 20 nm northwest of the accident site, included wind from 140 degrees at three knots, two statute miles of visibility in mist and clear skies. All major components of the aircraft were found at the accident site. Flight control continuity could not be established due to impact forces.