The flight departed Tulsa at 18:10 CST and routine position reports were made until over Dayton, Ohio, at 12:00. Over Dayton the aircraft entered icing conditions at the cruise altitude of 9000 feet. The crew requested permission twice to descend to a lower altitude to evade the icing conditions, but these requests were turned down. Around 12:35 the pilot reported “Difficulty maintaining altitude and airspeed request lower altitude.” At 12:37 Columbus CAA cleared the flight to descend to 8,000 feet msl. At approximately 12:40 witnesses observed the aircraft below the overcast; it was on a westerly heading and was descending although it appeared to be in a normal attitude. Several components were seen to separate from the aircraft before it struck the ground in a steep angle. PROBABLE CAUSE: “The Board determines that the probable cause of this accident was the accumulation of enough ice to result in loss of control and the subsequent shedding of vertical surfaces from the tail group of the aircraft.”