HISTORY OF FLIGHT On March 24, 2002, approximately 1930 central standard time, a Beech F35 single-engine airplane, N4257B, was substantially damaged following a structural failure of the airframe during cruise flight near Amarillo, Texas. The instrument-rated private pilot, who was the sole occupant of the airplane, was not injured. The airplane was registered to the Ron McMurray Family Limited Partnership and operated by the pilot. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The flight departed Clovis, New Mexico, approximately 1830, and was destined for Borger, Texas. The 2,500-hour pilot reported that while in level cruise flight at 140 knots indicated airspeed, at an altitude of 5,500 feet mean sea level (msl), the airplane encountered "clear air turbulence" approximately 20 nautical miles south-southwest of Amarillo. The pilot stated that at the time of the accident, the airplane autopilot system was engaged, and his hands were not on the cockpit controls. During the accident, the airplane "was suddenly thrust nose high and vertical." The pilot then "pushed the nose [of the airplane] over," and recovered control of the airplane from the unusual attitude. The pilot continued the flight to his intended destination; however, the autopilot system would not reengage, and the trim setting had to be readjusted to maintain level flight. The airplane landed uneventfully on runway 35 at the Borger Hutchinson County Airport (BGD). While tying down the airplane on the ramp in Borger, the pilot noticed damage to the empennage section. The pilot reported that at the time of the accident, the visibility was clear with no clouds and a weather front may have been developing near Amarillo. The NTSB was notified of the damage to the airplane on April 23, 2002, approximately one month after the accident. PERSONNEL INFORMATION The pilot held a private pilot certificate with an instrument rating. The pilot was issued a third class medical certificate on April 26, 2001, with the restriction, "Must have available glasses for near vision." The pilot had accumulated approximately 500 flight hours in the accident airplane. His most recent biennial flight review (BFR) was completed on January 2, 2002, in the accident airplane. AIRCRAFT INFORMATION The 1955 Beech F35 Bonanza, serial number D-4234, is a four place, low-wing, V-tail airplane with retractable landing gear. A review of the airplane's logbooks disclosed that an annual inspection was completed on July 8, 2001. At the time of the accident, the airplane had accumulated 418.7 total hours since the annual inspection and the airframe had accumulated 5,515.3 total hours. The airplane was equipped with a 225-horsepower Continental E-225-8 engine, serial number 36017-D-4-8-R, which was installed on May 25, 2000, and was equipped with a Beechcraft 215-208 propeller, serial number 3204. A review of the engine logbooks disclosed an annual inspection was completed on July 8, 2001. The total time on the engine at the time of the accident was unknown. According to the propeller logbook, the propeller was repaired and reinstalled on February 15, 2002, with no anomalies noted during the ground functional test. A review of the airplane's logbooks disclosed that on October 12, 1988, at a total time of 3,294 hours, the aircraft's empennage had a stabilizer leading edge cuff modification kit, Beech part number 35-4016-3, serial number 1590, installed in accordance with Beech drawing No. 35-4016. On June 29, 1995, Airworthiness Directive (AD) 94-20-04 (effective November 28, 1994), was completed. The AD required a one-time compliance within the next 100 hours time-in-service. On October 16, 1997, both ruddervators were removed, repainted, and reinstalled after a repair was completed. METEOROLOGICAL INFORMATION At 1853, the reported weather conditions at the Amarillo International Airport (AMA), Amarillo, located approximately 20 miles northeast of the occurrence site, were wind from 030 degrees at 22 knots, gusting to 27 knots, visibility 10 statute miles, sky clear, temperature 45 degrees Fahrenheit, dew point 28 degrees Fahrenheit, and an altimeter setting of 29.77 inches of Mercury. At 1911, the reported weather conditions at BGD, located approximately 50 miles northeast of the accident site, were wind from 010 degrees at 16 knots, visibility 10 statute miles, ceiling broken at 1,800 msl, temperature 37 degrees Fahrenheit, dew point 28 degrees Fahrenheit, and an altimeter setting of 29.86 inches of Mercury. At 1953, AMA reported wind from 020 degrees at 20 knots, gusting to 24 knots, visibility 10 statute miles, sky clear, temperature 36 degrees Fahrenheit, dew point 27 degrees Fahrenheit, and an altimeter setting of 29.82 inches of Mercury. A review of the AIRMETs and SIGMETs for the area revealed that AIRMET Tango was issued for the accident area and valid from 1445 until 2045. AIRMET Tango reported occasional moderate turbulence below 10,000 feet msl. No significant PIREPs were noted. WRECKAGE AND IMPACT INFORMATION On April 30, 2002, the airplane damage was examined in a hangar at the Borger Hutchinson County Airport by a Federal Aviation Administration (FAA) aviation safety inspector, FAA Wichita Aircraft Certification Office (ACO) representatives, and a representative from Raytheon Aircraft Company (RAC). The examination revealed that the aft fuselage damage was concentrated between the fuselage station (FS) 233.5 and 256.9 bulkheads. The aft fuselage exhibited extensive skin wrinkling and tearing between the FS 233.5 bulkhead and the FS 256.9 (front spar attachment). The rest of the aft fuselage exhibited no apparent deformation or cracks. The following damage to the fuselage was noted: 1. The left side of the fuselage exhibited a compression wrinkle extending from the bottom of the FS 256.9 bulkhead diagonally up and forward toward the top of the FS 233.5 bulkhead. The left side inspection panel was wrinkled and remained attached to the airplane. 2. There was fuselage skin wrinkling under the left stabilizer cuff. 3. The right side of the fuselage exhibited a compression wrinkle extending from the top of the FS 256.9 bulkhead diagonally down and forward toward the bottom of the FS 233.5 bulkhead. In addition, a compression wrinkle ran from the bottom of the FS 256.9 bulkhead diagonally up and forward until it met the other compression wrinkle that extended down and forward. 4. The aft end of the bottom fuselage skin was separated from the bottom of the FS 256.9 bulkhead. 5. The two L-stringers that extend along the bottom fuselage skin and attach to the bottom of the FS 256.9 bulkhead were separated from the bottom skin an average of 7 rivets each. 6. The bottom skin exhibited a compression wrinkle that extended from the middle of the FS 256.9 bulkhead forward and outward toward FS 233.5 bulkhead. 7. The left side of the bottom fuselage skin remained attached to the left fuselage side. 8. The right side of the bottom fuselage skin separated from the right fuselage side for 8 rivets forward of the FS 256.9 bulkhead. 9. No damage was observed to the FS 272, 256.9, or 233.5 bulkheads. 10. No damage was observed to the top of the fuselage. The following damage to the empennage was noted: 1. Both stabilizers were securely attached to the FS 256.9 bulkhead. Both ruddervators were securely attached to the stabilizers, and no damage was observed to either the left or right empennage assemblies. 2. Both ruddervators were checked for balance using the force method per the Bonanza 35 Series Shop Manual. The required static underbalance weight range is 16.8 to 19.8 inch-pounds (in-lbs.). The left and right ruddervators exhibited 19.0575 in-lbs. and 20.98 in-lbs. static underbalance, respectively. 3. The total weight of each counter balance assembly was 3 lbs 2 oz. The total weight consisted of a Beech conforming weight (P/N 35-660040-40), which weighed 2 lbs 7 oz., six lead washers, which weighed 5.5 oz and the counterbalance shell assembly. The counterweight assemblies were found securely attached. 4. The two ruddervator inboard hinge support bearings exhibited excessive radial wear. 5. The left ruddervator outer hinge bushing/bearing assembly and the right ruddervator center and outer hinge bushing/bearing assemblies exhibited excessive radial wear. 6. No improper rigging of the flight control system was noted. 7. The red trim paint color on the ruddervators did not match the airplane's red trim paint color. The following additional items were noted during the examination: 1. The engine tachometer hour meter read 2,186.0 hours. 2. The four engine mounts were examined. No indication of any separated rivets or working rivets was noted. No anomalies were noted with the shock mounts, they appeared to be in "good condition." The right ruddervator was retained for further examination. TESTS AND RESEARCH On September 9, 2002, the right ruddervator was examined at the facilities of RAC Process Laboratory under the supervision of the FAA ACO representative, a RAC process engineer and a RAC air safety investigator. The following items were noted at the examination: 1. The exterior skin surface of the ruddervator had been stripped of the red and white paint, which was present during the April 30th examination. 2. The counterbalance assembly was stripped of paint and loosely attached to the ruddervator. 3. The ruddervator trim tab was removed and not submitted for the examination. 4. The ruddervator skin was confirmed to be fabricated from magnesium by applying nitric acid solution to the skin which resulted in a bubbling action. 5. The ruddervator exterior skin thickness was measured with a micrometer at the cutout for the ruddervator trim tab cable, and at the ruddervator trailing edge where the skin overhung the trailing edge stiffener. The skin thickness was measured to be 0.0205 inches. Beech Drawing No. 35-660040 specifies a ruddervator skin thickness of 0.020 inches. 6. The interior surface of the ruddervator skin was covered with a paint that displayed a greenish tint. ADDITIONAL INFORMATION Radar information of the flight was not available due to the date of the NTSB notification. The airplane was released to the owner's representative.