Amateur-built CHALLENGER II N448WM accident near Praire Du Sac, Wisconsin

Probable cause

The separation of the fuselage-mounted wing strut attachment fitting for an undetermined reason, which resulted in the separation of the left wing of the airplane.

NTSB analysis

The airplane impacted the ground following an in-flight separation of the left wing during cruise flight. The pilot, who was the sole occupant, was fatally injured. Witnesses reported seeing the airplane traveling north, about 300-500 feet above ground level, when one wing suddenly separated from the airplane. One of the witnesses stated that the other wing separated shortly after the first one. Postaccident examination confirmed that both wings were completely separated from the airplane with the exception of the right wing aft spar and aileron. Examination of the fractures in the wing attachment fittings revealed signatures consistent with overload failure with the exception of one fitting that had no perceptible damage due to deformation or fracture. The attachment bolt for the fitting that showed no perceptible overload damage was not recovered during the investigation; however, the relative lack of damage to the strut fitting indicates that the attachment bolt either failed, or its corresponding nut had loosened and separated during the flight. A portion of wing fabric retained for testing showed that the fabric met the minimum performance requirements as set forth in regulations. No preaccident defects were found with regard to the components examined.

Text from the NTSB. Open the NTSB docket for CEN11LA050 for the full record.