On August 10, 1993, at 1900 central daylight time, a Beech F35, N5064B, was substantially damaged during descent near Mena, Arkansas. The private pilot was not injured. Visual meteorological conditions prevailed for the personal flight. In a prepared written document and during a telephone interview, the pilot stated he initiated his descent from 4,500 feet, increasing his indicated airspeed to 180 mph. After announcing his position in the downwind leg at the Intermountain Airport at Mena, Arkansas, while at 155 mph, a severe vibration developed throughout the airframe. The pilot further stated that he closed the throttle and extended the landing gear in a attempt to slow down the airplane. The oscillations and vibration decreased as his airspeed decreased, and a normal landing was executed. No turbulence was encountered at any time during the descent or the approach. Examination of the airplane on the ramp revealed that the outer portion of the right ruddervator outboard of the center hinge, and the counter weight for the left ruddervator had separated from the airframe in flight. Substantial twisting, buckling, and skin tearing were also found in the aft section of the empennage. Both ruddervators (p/n 35-660040-607 and 608 respectively) were removed from the airplane and shipped to the manufacturer's lab for further evaluation and testing. All parts that separated from the airplane in flight were recovered, with the exception of the counter weight for the left ruddervator. A detailed examination and inspection was conducted by Beech engineers. The investigation concluded that both ruddervators were out of balance due to a combination of unauthorized sheet metal repairs, improper paint application techniques, and the use of a locally manufactured counter weight. A copy of the their examination report is enclosed in this report.