History of Flight
On September 8, 2013, at about 1130 Pacific daylight time, an experimental amateur-built Cantrell LW Challenger II SP airplane, registration N65VG, was substantially damaged when it impacted terrain near Prineville Airport (S39) in Prineville, Oregon. The airplane was operated by the pilot under 14 CFR Part 91. The sport pilot, the sole occupant, was fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight, which departed from S39 about 1100.
Witnesses near the accident site reported observing the airplane flying at low altitude. They stated that the airplane oscillated upward and downward three times and the tail flight control surfaces appeared to move erratically before the airplane descended nose-down into terrain. One witness reported that the engine may have lost power before losing sight of the airplane. Another witness stated that the propeller appeared to be operating but the engine did not sound normal.
Wreckage and Examination
Examination by a Federal Aviation Administration (FAA) inspector revealed that the airplane came to rest on its left side. The wing structure was separated and found forward of the main wreckage. All major structural components were located within about 20 feet of the main wreckage.
Personnel Information
The pilot, age 46, held a sport pilot certificate and a second-class airman medical certificate issued on June 27, 2013, with the limitation "must have glasses available for near vision." The pilot's logbook indicated a total of 73 hours of flight time as of September 1, 2013.
Aircraft Information
The amateur-built, two-seat, high-wing, fixed-gear tailwheel-equipped airplane, serial number CW1165, was completed in 1997. It was powered by a Rotax 503 engine, serial number 4838245, rated at 50 horsepower. The pilot and his son purchased the airplane on April 9, 2012.
Meteorological Information
A review of data from the Redmond Municipal Airport automated weather observation station, about 11 miles west of the accident site, at 1156 reported wind variable at 6 knots, visibility 10 statute miles, clear sky, temperature 22°C, dew point 9°C, and an altimeter setting of 30.12 inches of mercury.
Medical and Pathological Information
An autopsy conducted by the Oregon State Medical Examiner on September 10, 2013, determined the cause of death as "multiple blunt force traumatic injuries." Toxicology tests performed by the FAA's Civil Aeromedical Institute (CAMI) were negative for carbon monoxide, cyanide, volatiles, and drugs.
Tests and Research
Examination of the wreckage by the National Transportation Safety Board (NTSB) on October 22, 2013, revealed that both wings were separated for transport. The ailerons, rudder, and elevator remained attached. Both left and right elevator control torque tubes were fractured. The left torque tube exhibited chaffing near the fracture area, and striations were observed on the fuselage tube structure adjacent to the torque tube. Impact marks were found on the bottom left side of the vertical stabilizer and on the bottom side of the left horizontal stabilizer, with puncture holes in the fabric. A trim tab on the left elevator had a loose bolt attaching it to the actuating arm.
The trim tab and torque tubes were sent to the NTSB Materials Laboratory. Examination showed that both control tube assemblies fractured between the aft rod end and the center tube, adjacent to the aft end of the outer torque tube sleeve. Fracture features were consistent with overstress fracture from bending forces. The forward rivet for the left control tube sleeve was missing; the corresponding through-holes measured 0.125 inch. The manual for the Challenger II specified installation of 1/8-inch stainless steel rivets at four positions on the elevator torque tube.
The engine was examined: it remained attached, carburetor detached, spark plugs normal, crankshaft rotated with thumb compression on all cylinders, carburetors unremarkable with clean fuel. No preimpact mechanical malfunction was found that would have precluded normal operation.
Additional Information
In an interview, the pilot's son reported that both he and his father knew the airplane experienced abnormally high vibrations from the tail during high-speed flight (approaching 90 mph), causing the control stick to slam forward. They found an article suggesting adjusting the elevator 3 degrees would help, but did not troubleshoot the cause. The mechanic who performed the last condition inspection on June 10, 2013, noted no abnormal wear on elevator flight controls but observed a buffet during throttling back in descent, which he attributed to the pusher engine. The pilot had mentioned similar vibrations at 90 mph. The mechanic and pilot inserted gap strips between the horizontal stabilizer and elevators and increased the elevator angle of incidence, but the method was uncertain.