WPR13FA056

The pilot's decision to perform aerobatics in an airplane that was prohibited from aerobatics as stated in its operating limitations document, which resulted in the failure of the right wing spar.

The purpose of the flight was for the pilot-rated passenger to show the owner/pilot how to perform rolls in the experimental kit-built airplane. A witness reported observing the airplane in level flight about 1,000 feet above ground level before it entered a steeply banked turn. The airplane was halfway through the turn when the right wing folded up over the fuselage. The wing departed the airframe, and the airplane rapidly descended to the ground. The right wing was located about 1,090 feet from the main wreckage. The owner/pilot was not the builder of the airplane, and he had no record of aerobatic flight experience. The pilot-rated passenger's logbook indicated that he had made a single 0.5-hour flight in another RV-6 that included performance of rolls and wing-overs. The operating limitations document for the airplane noted that aerobatic flight was prohibited unless such flights were satisfactorily accomplished and recorded in the aircraft logbook during its flight test period. No entries were found in the logbook that would satisfy this requirement. Postaccident examination of the separated right wing determined that the upper and lower spar-caps had failed in buckle and overload. Although the airplane was registered with the Federal Aviation Administration by the builder as an RV-6-CH model, the design of its spar caps was found to be substantially different from the kit manufacturer's design for the RV-6 model airplane, a model which can be approved for aerobatic maneuvers. Rather the design was similar to the wing cap spar design for the older RV-3 model airplane, a design which was found to be susceptible to failure in buckle when exposed to aerobatic flight. Following a number of inflight wing failures in RV-3 airplanes during aerobatic flight, the kit manufacturer recommended that no aerobatic maneuvers be performed in RV-3 model airplanes until wing spar modifications that increase the spar's stiffness and resistance to buckling have been accomplished. Because the purpose of the flight was performance of an aerobatic maneuver (rolls) and because the airplane's wing spar cap design was not suitable for aerobatic flight, it is likely that at some point during the flight, an aerobatic maneuver was performed that weakened the wing, and the final steep turn was then sufficient to overload the wing. Toxicology results showed that the owner/pilot had therapeutic levels of diphenhydramine, a sedating antihistamine, in his system; however, it could not be determined if he was flying at the time of the accident or if this impairment contributed to the accident.

The right-wing spar was sectioned out of the wing, and the wing carry through spar was sent to the National Transportation Safety Board's Materials Laboratory for a detailed examination. The entire Materials Laboratory Factual Report is contained in the official docket for this investigation. The right wing separated approximately 1 foot from the centerline of the center section. The left wing remained attached to the center section. The wing structure was disassembled on-site from the fuselage to facilitate shipping, handling, and examination. The wing section contained a forward and aft spar. The forward spar at the fracture location contained a total of four reinforcement pieces for the web; nine reinforcement strips (1.5 inch by 0.125 inch) for the upper spar cap; and nine reinforcement strips (1.50 inch by 0.125 inch) for the lower spar cap. Examination of the forward spar revealed that the fracture faces of the lower spar cap at the inboard side contained less mechanical damage compared to those on the upper spar cap pieces. The aft spar contained an attachment plate with two holes (about 0.75-inch diameter, each). When intact, the attachment plate extended between the aft spar of the center section and the aft spar of the right wing. The attachment plate is designed to be attached by rivets to the upper and lower brackets of the aft spar for the right wing. The inboard end of the plate is designed to be attached by two bolts and corresponding nuts to the aft spar of the center section. Examination of the attachment plate revealed the attachment rivets between the center section and right wing fractured at the shank. The fracture faces of the rivets exhibited metal flow consistent with ductile separation in shear mode. The outboard end of the attachment plate was deformed up and aft relative to the aft spar of the center section. The upper and lower brackets remained attached to the aft spar of the right wing. Microscope examination of the fracture faces on the forward and aft spar sections of the wing structure and those on the center section showed gray-granular rough features on a slant plane consistent with overstress separation with no evidence of fatigue cracking. RV-3 History Van's Aircraft Service Bulletin SB-96-3-1, dated March 25, 1996, states in the synopsis, "After a number of in flight wing failures in RV-3 and RV-3A aircraft. Studies were initiated to identify any possible design deficiencies. These studies resulted in a recommendation by Van's Aircraft and the FAA to limit aerobatic flight of affected aircraft until main wing spar modifications have been accomplished." The RV-3 wing spar design utilized a spar-cap stack up of 0.125-inch bar stock. This design was found to be susceptible to failure in buckle when exposed to aerobatic flight or high g-loading. An extensive discussion regarding this issue was addressed in Van's Aircraft RV-3 Safety Alert, dated March 25, 1996. The Van's RV-6 wing spar design resolves the RV-3's spar failure issue by increasing the spar stiffness and resistance to buckling by increasing bar stock thickness from 0.125 to 0.25-inch bar stock in the wing spar stack up and construction. An autopsy was performed on the pilot on November 11, 2012, by the Oregon State Medical Examiner, Clackamas, Oregon. The cause of death was listed as "blunt force injuries of head and chest." The FAA Forensic Toxicology Research Team performed toxicology on specimens from the pilot with positive results for diphenhydramine detected in blood (0.604 ug/ml), and ethanol detected in muscle (20 mg/dl), no ethanol was detected in the brain. Diphenhydramine is a sedating antihistamine used to treat allergy symptoms and as a sleep aid. It is available over the counter under various trade names including Benadryl and Unisom. Diphenhydramine carries the following warning: may impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery). There was an insufficient specimen amount to test for carbon monoxide, and the test for cyanide was not performed. An autopsy was performed on the pilot-rated passenger November 27, 2012, by the Oregon State Medical Examiner, Clackamas. The cause of death was listed as, "Craniocerebral and chest trauma." The FAA Forensic Toxicology Research Team performed toxicology on specimens from the passenger with negative results for carbon monoxide, screened drugs, or ethanol. The two seat, low wing, fixed gear, tail-wheel configured airplane, serial number AC-3, was an experimental amateur-built airplane manufactured in 1996. The majority of the airframe was designed and built by an individual that was previously employed at Van's Aircraft. A second party bought the partially constructed airplane and completed the construction. The airplane was purchased by the pilot on May 29, 2012. The date of manufacture that is recorded on the FAA registration is 1996. The Federal Aviation Administration (FAA) letter defining N424D's Experimental Operating Limitations was dated May 17, 1996. Under Phase II of the Experimental Operating Limitations, subsection titled "The Following Limitations Apply Outside of Flight Test Area", line 4 states, "This aircraft is prohibited from acrobatic flight, unless such flight were satisfactorily accomplished and recorded in the aircraft logbook during the flight test period." Examination of the airplane's maintenance logbooks did not include any such entry that would satisfy this requirement. The airplane was powered by a Continental IO-346-A, 165-horsepower engine, and equipped with a wooden fixed-pitch propeller. A review of copies of the airplane maintenance logbooks revealed that the most recent conditional inspection was performed on May 25, 2012, at a total airframe time of 557 hours. Although the airplane was designated an RV-6-CH and closely resembled the Van's RV-6 model of airplane, there were numerous differences between the accident airplane and the kit design that Van's Aircraft produces. The wing span of the accident airplane, as measured after the accident, was 22 feet. In contrast, the Van's RV-3 wing span is 20 feet, and the Van's RV-6 is 23 feet. There were additional differences in the wing spar construction. The wing spar construction of the accident airplane utilized the same materials and general design as the Van's RV-3 series of designs and the wing appeared to be a modified and extended version of the RV-3 wing. The original Van's RV-3 wing spar design consists of a 0.040 aluminum channel web with a build-up of seven 0.125 by 1.25-inch bars riveted together on to form the upper and lower spar caps. The accident airplane's spar consisted of a build-up of 4 pieces of aluminum channel web with nine 0.125 by 1.5-inch aluminum bars for the upper and lower spar caps. In contrast, the Van's RV-6 uses 2 pieces of 0.040 2043-T3 aluminum channel web with a build-up of four 0.250 by 1.5-inch aluminum bars plus one 0.125 by 1.5-inch bar. The pilot, age 46, held a private pilot certificate with ratings for airplane single-engine land and instrument airplane, issued June 4, 2010. He additionally held a third-class medical certificate with the limitation that he wear corrective lenses, issued April 2, 2012. Examination of the pilot's logbook revealed that as of November 25, 2012, he had accumulated 1,005.0 total flight hours of which 48.5 hours were in the accident airplane. On June 8, 2012, he received a tail wheel endorsement, an endorsement to act as pilot-in-command in a Vans RV-6 or RV-7 series aircraft, and a flight review. No record of aerobatic instruction was found in his logbook. The passenger, age 45, held a commercial pilot certificate with an airplane single-engine land rating issued June 26, 2012, and a second-class medical certificate with the limitation that he wear corrective lenses issued on May 22, 2005. Examination of his logbook revealed tha