Chicago & Southern Airlines Flight 804 was destroyed in an accident near Peoria-Greater Peoria Airport, Illinois. All sixteen on board were killed. The aircraft made initial contact with powerlines which cross the midpoint of the instrument final approach course, approximately 3,2 km west of runway 12 of the Greater Peoria Airport. The aircraft thereafter contacted the ground, bounced and slid into the base of a large hedgewood tree 152 feet from the point of initial wire contact. An intense fire ensued which almost completely destroyed the cockpit and cabin area of the fuselage. The ATECO Westwind II airplane was a Beechcraft E18S that was converted with a 7 feet fuselage extension and fitted with tricycle landing gear and turboprop engines. The Board determines that the probable cause of this accident was that the pilot knowingly descended below the Minimum Descent Altitude in an attempt to complete the approach by means of visual reference to ground objects. Because of minimal visibility and low clouds in the approach zone, the aircraft was operated at an altitude too low to provide clearance over the powerlines.