NTSB Factual Report

HISTORY OF THE FLIGHT

On November 26, 2012, at 1537 Pacific standard time, a McDaniel RV-6-CH, N424D, collided with terrain after its right wing departed the airplane 5 miles south of Scio, Oregon. The airplane was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations, Part 91. The private pilot and the commercial pilot were fatally injured. The airplane was substantially damaged. Visual meteorological conditions prevailed, and a flight plan had not been filed. The personal flight originated at the Lebanon State Airport, Lebanon, Oregon, at 1531.

A witness described observing the airplane at 1,000 feet above ground level (agl). When the airplane was halfway through a turn, one of the wings folded up. The airplane then rapidly descended to the ground. The Linn County Sheriff's office reported that the airplane's right wing was located on Highway 226, and the main airplane wreckage was located in a pasture 1,090 feet south of the wing.

The Fixed Base Operator (FBO) proprietor at Lebanon State Airport stated that the pilot and commercial pilot-rated passenger were acquaintances. The pilot arrived earlier that day at Lebanon State Airport and met up with his passenger. The passenger had a set of portable remote cameras that he was going to mount onto the foot step on the airplane to video record the flight. Additionally, the pilot-rated passenger intended to show the pilot how to perform rolls.

PERSONNEL INFORMATION

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 that he had accumulated 590 total flight hours as of November 23, 2012, and his most recent flight review was on February 8, 2012. The logbook showed a single entry dated November 5, 2012, for 0.5 hours in a RV-6A, and the comment line states, "Rolls & wing overs." No other entries were found that included experience in Vans RV model of airplanes or of aerobatic instruction.

AIRPLANE INFORMATION

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.

MEDICAL AND PATHOLOGICAL INFORMATION

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.

WRECKAGE AND IMPACT INFORMATION

The right wing was located on a highway paved with asphalt. The wing root and 2-3 rib bays had been crushed longitudinally into the wing. The inboard portion of the main wing spar, in the vicinity of the longitudinal crushing, was buckled in the shape of a double-S. Located in the center of the highway there was an indentation in the asphalt that was consistent with wing impact, and in the adjacent area was the odor of aviation fuel and fuel stains were observed. The wing's aft spar doubler plate was not present on the spar. The upper and lower spar caps were bent aft and outward, pointing down the wing span towards the wing tip. The lower spar-cap of the rear spar, at the attach bolt-hole location, was missing a section of material originating at the bolt hole. The aileron and flap were present on the wing, the aileron control rod was connected to the aileron, and the control rod had separated at the wing root. The wing skin did not exhibit any wrinkling or buckling.

A debris field extended from the right wing to the main wreckage and mostly consisted of Plexiglas fragments, and small cockpit items. The reported remote video camera that may have been mounted to the foot step was not located. Blister packs of Nicorette (4mg/piece) and Benadryl Allergy (25mg Diphenhydramin HCl liquid-gels) were identified in the debris.

The main wreckage was located about 1,090 feet to the south of the right wing, in a grass pasture, resting on its right side. It was oriented from tail to nose on a bearing of 138 degrees magnetic. The wreckage consisted of the left wing, fuselage, cockpit, tail, engine, and propeller. Flight control continuity was established on-scene by manually moving the aileron and elevator control surfaces and observing movement of the control stick in the cockpit area. Control continuity from the rudder to the cockpit was established by tracing the rudder cables from the rudder control surface attachment point to the rudder pedal cable anchors on the rudder pedals. The left horizontal stabilizer and vertical stabilizer appeared undamaged; the right horizontal stabilizer and elevator exhibited crush damage from ground impact. The left wing laid on top of and in line with the fuselage. The left wing main spar was continuous through the cabin and extended 14 inches into the right wing spar where it was fractured completely at the upper and lower spar caps. In the region of the fracture surfaces the spar ends were bent aft. The upper and lower spar caps were a buildup of 9, 0.125 thick aluminum bars and bolted together with through-bolts positioned every 1.25 inches. The fracture surface of each bar appeared bright and angular, with shear lips. The aft spar of the left wing remained attached to the carry through. The right side of the aft wing spar carry though contained the right wing aft-spar doubler plate and spar attach-bolt.

The cockpit cabin had been completely compromised, and the right side of the engine had imbedded about 2 feet into the ground. The right underside of the engine's case and oil pan had been broken and torn laterally. The right case-half contained a crack at the no. 3 cylinder location. The two magnetos had been displaced from their mounting pads. The right magneto produced spark at three terminals when rotated by hand; the left magneto was seized and could not be rotated by hand. The upper spark plugs were removed. The spark plugs were dark gray in color, all gaps were similar, and no mechanical damaged was observed. The engine was seized and could not be rotated by hand. The fuel distribution valve was intact, no debris was observed in the filter screen, and fuel was observed in the valve. The wood propeller was attached to the propeller hub. One blade was fractured at the hub, the other blade extended out 20 inches from the hub. A majority of wood blade-fragments were recovered with the engine.

TESTS AND RESEARCH

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.

ADDITIONAL INFORMATION

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.

NTSB Probable Cause

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.