On June 23, 1996, at 2130 central daylight time, a Beech B-35, N5001C, sustained substantial damage when it encountered moderate turbulence during cruise near Chesterfield, Missouri. After landing, the pilot inspected the airplane and discovered structural damage to the fuselage and stabilators. The private pilot reported no injuries himself or to the one passenger. The 14 CFR Part 91 flight departed Jefferson City, Missouri, en route to Chesterfield, Missouri. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that he was flying at 2,500 feet mean sea level (MSL) at 140 MPH. He reported encountering light turbulence and that the airplane started to shake. The shaking lasted for about three seconds before he could reduce the power and pull back on the yoke. He slowed the aircraft and was able to continue on to his destination where he made a normal landing. In a separate statement to the Federal Aviation Administration (FAA), the pilot indicated that the airspeed may have been higher than what was initially reported. The pilot reported to the FAA that the airspeed was 5 to 10 knots over the Red Line of 125 knots that was marked on the airspeed indicator. An examination of the aircraft and logbooks by an Airworthiness Inspector of the FAA revealed that the aircraft did not have a current annual inspection. An inspection of the pitot tube revealed that there were pinholes in the tube where it had been welded. The airspeed indicator was tested and it was determined that it did not meet specifications. Maintenance records and invoices indicated that the aircraft was extensively refurbished between November 1994 and May 1995. An invoice dated March 9, 1995, indicated that the trim tabs were installed on the ruddervators and were rigged and balanced. The annual inspection was signed on May 20, 1995. Included in the annual inspection sign-off was the statement, "Installed overhaul + balanced ruddervators." The aircraft logbook indicated that the aircraft was painted on August 16, 1995. The logbook entry reads: "...Ailerons, flaps, and ruddervators were removed. Repainted and reinstalled I.A.W. Manufacturers Specifications. The static balance check on the ailerons and ruddervators has been done. Aircraft approved for return to service." An inspection of the aircraft by the National Transportation Safety Board (NTSB) revealed extensive structural damage to the empennage of the airplane. The ruddervators were examined for proper balance and rigging. The service balance range for the ruddervators was 16.8 to 19.8 inch-pounds trailing edge heavy (underbalance). Using the counterbalance method, the underbalance of the left and right ruddervators was determined to be 22.53 and 22.68 inch-pounds, respectively. The lead counterweight in the left ruddervator balance horn weighed 1.94 pounds. Some of the lead had been removed by drilling and there were no mounting screws or washers installed. The lead counterweight for the right ruddervator weighed 2.17 pounds. Six lead washers of undetermined origin were attached and weighed 0.32 pounds. Both the left and right ruddervator trim tab hinge pins had been installed incorrectly. The left hinge pin was removed and reinstalled correctly for comparison purposes. The correctly installed tab exhibited no free play and could be rotated easily up and down. By comparison, the incorrectly installed right trim tab exhibited significant vertical free play near its inboard end and restricted up and down angular travel. (See Structural Factual Report)