History of 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 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 no flight plan was filed. The personal flight originated at Lebanon State Airport, Lebanon, Oregon, at 1531.
A witness observed the airplane at 1,000 feet above ground level. When the airplane was halfway through a turn, one of the wings folded up, and the airplane 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 proprietor at Lebanon State Airport stated that the pilot and commercial pilot-rated passenger were acquaintances. The pilot arrived earlier that day and met with the passenger. The passenger had a set of portable remote cameras that he intended 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 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 a total of 1,005.0 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 May 22, 2005. Examination of his logbook revealed 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, with the comment, "Rolls & wing overs." No other entries included experience in Vans RV model airplanes or aerobatic instruction.
Aircraft 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 previously employed at Van's Aircraft. A second party bought the partially constructed airplane and completed construction. The pilot purchased the airplane on May 29, 2012. The FAA registration records the date of manufacture as 1996. The FAA letter defining N424D's Experimental Operating Limitations was dated May 17, 1996. Under Phase II, the limitations state: "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. 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, there were numerous differences. The wing span, 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. The wing spar construction utilized the same materials and general design as the Van's RV-3 series, and the wing appeared to be a modified and extended version of the RV-3 wing. The accident airplane's spar consisted of a buildup of 4 pieces of aluminum channel web with nine 0.125 by 1.5-inch aluminum bars for the upper and lower spar caps. The Van's RV-6 uses 2 pieces of 0.040 2043-T3 aluminum channel web with a buildup of four 0.250 by 1.5-inch aluminum bars plus one 0.125 by 1.5-inch bar.
Wreckage and Impact Information
The right wing was located on a highway paved with asphalt. The wing root and 2-3 rib bays were crushed longitudinally into the wing. The inboard portion of the main wing spar was buckled in a double-S shape. An indentation in the asphalt was consistent with wing impact, and aviation fuel odor and 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. 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; the aileron control rod was connected to the aileron and had separated at the wing root. The wing skin showed no wrinkling or buckling.
A debris field extended from the right wing to the main wreckage, consisting mostly of Plexiglas fragments and small cockpit items. The reported remote video camera was not located. Blister packs of Nicorette (4mg/piece) and Benadryl Allergy (25mg Diphenhydramine HCl liquid-gels) were identified in the debris.
The main wreckage was located about 1,090 feet south of the right wing, in a grass pasture, resting on its right side, oriented 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. The left wing main spar was continuous through the cabin and extended 14 inches into the right wing spar, where it fractured completely at the upper and lower spar caps. Fracture surfaces appeared bright and angular with shear lips. The cockpit cabin was completely compromised. The right side of the engine was embedded about 2 feet into the ground. The engine case and oil pan were broken. The wood propeller was attached; one blade was fractured at the hub, and the other extended 20 inches from the hub.
Additional Information
Van's Aircraft Service Bulletin SB-96-3-1, dated March 25, 1996, states: "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 0.125-inch bar stock, found susceptible to failure in buckle under aerobatic flight or high g-loading, as addressed in a Van's RV-3 Safety Alert dated March 25, 1996. The RV-6 wing spar design resolves this by increasing bar stock thickness to 0.25-inch.
Medical and Pathological Information
An autopsy performed on the pilot on November 11, 2012, listed cause of death as "blunt force injuries of head and chest." The FAA Forensic Toxicology Research Team tested pilot specimens and detected diphenhydramine in blood (0.604 ug/ml) and ethanol in muscle (20 mg/dl), no ethanol in brain. Diphenhydramine is a sedating antihistamine with warnings about impairing mental/physical ability. Insufficient specimen for carbon monoxide testing; cyanide test not performed.
An autopsy on the pilot-rated passenger on November 27, 2012, listed cause of death as "craniocerebral and chest trauma." Toxicology on the passenger was negative for carbon monoxide, screened drugs, or ethanol.
Tests and Research
The right-wing spar and wing carry-through spar were sent to the NTSB Materials Laboratory for examination. The right wing separated approximately 1 foot from the centerline of the center section. The forward spar fracture faces showed gray-granular rough features on a slant plane consistent with overstress separation, with no evidence of fatigue cracking. The aft spar attachment plate rivets fractured in ductile separation in shear mode. The outboard end of the attachment plate was deformed up and aft. Microscope examination confirmed overstress separation throughout.