Urbana, IL, USA
N4668D
Beech BE-G35
The airplane sustained substantial damage to the left stabilator spar while performing a steep turn maneuver. The pilot stated his airspeed was about 120 miles per hour when entering the maneuver and he did not recall his airspeed increasing any more than five knots during the maneuver. The pilot indicated that as he was performing the left steep turn he began to lose altitude and increased elevator pressure to correct for the altitude loss. He reported that on recovery the control yoke began to vibrate and the rudder pedals began to "advance back and forth rapidly." The pilot stated he released the backpressure on the controls and landed without incident. Review of the airplane's logbooks showed that both ruddervators had been recently reskinned, painted, and balanced. An examination of the airplane revealed the ruddervator trim tabs had been installed upside down and that the trim tab wire had been threaded improperly. The ruddervators were balanced and the left ruddervator was determined to be 19.86 inch pounds underbalance, with the allowed underbalance moment range being 16.80 to 19.80 inch pounds. The on-site inspection revealed a crack in the left stabillator spar. The fracture initiated at the top of the spar that attaches to the bulkhead, migrated through the top outboard bolt hole, and progressed to the bottom outboard bolt hole.The metallurgical examination revealed that the fracture of the main spar of the left stabilator was representative of a tension overload along the full length of the fracture zone.
On February 9, 2003, at 1400 central standard time, a Beech BE-G35, N4668D, sustained substantial damage while maneuvering. The Title 14 CFR Part 91 personal flight departed Frasca Field (C16), Urbana, Illinois, on a local training flight. The pilot had performed chandelles, lazy eights, and was performing steep turns when the rudder pedals began to vibrate while in a left turn. The pilot landed at C16 without incident. Ground inspection revealed that the left ruddervator was loose, the left stabilator spar was cracked, and the fuselage was wrinkled ahead of the ruddervators. The pilot was not injured. Visual meteorological conditions prevailed. No flight plan was filed. The pilot reported he was performing lazy eights, chandelles, and steep turns. He stated that as he reversed a steep turn to the right and entered a steep turn to the left, he noted his vertical speed indicator (VSI) was indicating a descent and that his altimeter was indicating less than his desired altitude of 3,000 feet above ground level. The pilot stated that he increased back pressure on the controls, at which point he heard felt a "shaking" and the rudder pedals "advanced back and forth rapidly." The pilot stated he decreased his elevator pressure and the vibration stopped. The pilot reported he reduced engine power and proceeded back to C16. The pilot indicated he performed a normal landing without incident. The pilot reported he noticed the damage to the tail of the aircraft after he had taxied back to the hanger and exited the aircraft. The pilot reported he lost about 100 feet during the descent, but did not notice the loss in altitude until about 180 degrees through the turn. Review of the airplane's logbooks revealed that the airplane had 6,262 hours total airframe time. The last annual inspection was conducted on April 16, 2002 at 6,172 hours. The pitot static system had been tested on January 24, 2002 at 6,162 hours. The Beech Mandatory Service Bulletin 2188, which required the structural inspection and installation of a stabilizer reinforcement kit, was complied with on July 2, 1987. Both ruddervators were reinstalled on January 7, 2003, after being reskinned, painted, and balanced. A Walker Engineering Ventral Air Skag, supplemental type certificate (STC) SA3337WE, had been installed on the aircraft on August 9, 1978. A Federal Aviation Administration (FAA) airworthiness inspector, an aviation safety investigator from the Raytheon Aircraft Company (RAC), and a technical representative from the American Bonanza Society, conducted an examination of the airplane on February 11, 2003. The examination revealed wrinkles in the aft fuselage between the fuselage station (FS) 233.5 and FS 256.9 bulkheads. Two stringers were found bent on the right side of the fuselage, and one was found bent on the left side. Wrinkles were also found on the bottom of the fuselage between the FS 256.9 bulkhead and FS 246 in a pattern resembling an "X." Examination of the ruddervators revealed that the trim tabs had not been installed in accordance with the manufacturer's specifications. The trim tabs had been installed upside down; the flat surfaces were mounted facing down and the curved surface mounted facing up. The ruddervator trim tabs on the G model of the Beech BE-35 should be installed with the cambered (curved) side facing down and the flat side facing up. The examination also revealed that the trim tab wires in the trim tab hinges had been improperly installed. The ruddervators were removed and their balance was checked using the counterbalance method. The allowed underbalance moment range is 16.80 to 19.80 inch-pounds. The left ruddervator was determined to be 19.86 inch-pounds static underbalance and the right ruddervator was determined to be 19.41 inch-pounds static underbalance. The left counter balance weight assembly weighed 3 pounds, 7.4 ounces, and the right counter balance weight assembly weighed 3 pounds, 2.5 ounces. (See RAC letter dated July 2, 2003, Accident Report) The left stabilator of the airplane was sent to RAC for a metallurgical examination. The examination focused on a fracture found on the main spar of the left stabilator. The metallurgical examination revealed that the slant fracture was representative of a tension overload along the full length of the fracture zone. The fracture surface color was uniform throughout the fracture zone, with no indication of fatigue cracking on any of the fracture surfaces. A Rockwell hardness test and an electrical conductivity test revealed that the two spar stub end pieces produced values acceptable for aluminum alloy 2024. (See RAC letter dated May 9, 2003, Metallurgical Report) Parties to the investigation included the Federal Aviation Administration, Raytheon Aircraft Company, and the American Bonanza Society.
The partial failure of the left stabilizer in overload.
Source: NTSB Aviation Accident Database
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