History of the Flight
On November 1, 2010, at approximately 1415 central daylight time, the amateur-built McFarland Challenger II, registration N448WM, sustained substantial damage when it struck the ground after the left wing separated in flight. The airplane was piloted by the sole occupant and operated under 14 CFR Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed Sauk Prairie Airport near Prairie Du Sac, Wisconsin, around 1400, en route to Merrill Municipal Airport. Witnesses observed the airplane traveling north when one wing detached, shortly followed by the other. They estimated the altitude before the first separation at 300 to 500 feet above ground. The airplane then crashed into a cornfield.
Aircraft Information
The airplane was a high-wing, tricycle-gear kit aircraft constructed of aluminum alloy tubing fastened with bolts and rivets, covered with fabric. It was equipped with amphibious floats and seating for two in tandem. Power was provided by a 65-horsepower Rotax 582 engine in a pusher configuration. According to FAA records, the aircraft received experimental amateur-built certification on July 14, 2004. The pilot acquired it from the original builder's widow on August 20, 2010.
Meteorological Information
Data from the Baraboo Wisconsin Dells Airport automated weather station, elevation 979 feet, recorded at 1415: calm winds; visibility 10 miles; scattered clouds at 3,200 feet; temperature 8°C; dew point 0°C; altimeter 30.42 inHg.
Wreckage and Impact Examination
The airplane impacted a harvested cornfield, with components coming to rest in three major groups: the left wing, right wing, and fuselage. The fuselage remained upright with its lower section crushed upward. The rudder and vertical stabilizer stayed attached to the aft fuselage. The right horizontal stabilizer and elevator separated and were found near the left wing; the left horizontal stabilizer and elevator were located near the aft fuselage in their approximate normal positions. Both wings completely separated except for the right wing aft spar and aileron, which remained attached to the fuselage. The forward right wing attach fitting was fractured. The left wing separated from the fuselage with both attachment fittings fractured. Fabric covering was torn; a large portion of the left lower wing covering was found nearby. The left rear spar and control surfaces showed uniform bending along the entire span, resulting in upward curvature.
Nine wing attachment fittings with deformation or fracture were retained for examination. The NTSB Materials Laboratory found overload failure signatures on all fractured parts. Non-fractured parts showed plastic deformation except one: the left-rear-lower wing strut attachment fitting connecting the wing strut to the fuselage, which had no perceptible damage. Its attachment bolt was not recovered.
A piece of left wing fabric covering was tested per ASTM D 5035-08; average breaking strength was 67.75 pounds. FAA minimum performance standards for new intermediate grade fabric (TSO-C14B) require at least 65 pounds. No preaccident defects were identified in the examined components.
Medical and Pathological Information
An autopsy performed on November 2, 2010, by the University of Wisconsin School of Medical and Public Health attributed the pilot's death to injuries sustained in the accident. Toxicology tests by the FAA Civil Aerospace Medical Institute were negative for all screened substances.