Zenith Aircraft Co ZODIAC 601 XL N538CJ accident near Agnos, Arkansas

Probable cause

The in-flight separation of both wings due to aileron flutter. The aileron flutter was the result of inadequate wing stiffness and strength and the lack of aileron counterbalances.

NTSB analysis

The light-sport airplane experienced an in-flight break-up during a cross-country flight. Flight track data recovered from an onboard global positioning system, and a subsequent performance study, depicted the airplane was maneuvering between the altitudes of 2,500 and 3,500 feet at airspeeds between about 60 and 108 knots calibrated airspeed (KCAS). The airplane performed a number of turns and maneuvers during the hour-plus flight, including a landing approach and pass over an airport. The calculated bank angle for the entire flight never exceeded 30 degrees. At the time when the breakup occurred, the airplane was climbing at about 500 feet per minute through 2,800 feet altitude and had accelerated to 100 KCAS. The estimated angle of attack was about 3 degrees during the last minute of the flight, and the airplane wreckage was spread over 600 feet on the ground. An examination of the airplane wreckage revealed compression buckling and upward and downward bending of both wings. The upward and downward movement, twisting, and flexing of the airplane wing surface was consistent with the occurrence of aerodynamic flutter. In addition, damage was noted on the flap assemblies consistent with over travel. Ultimately both wings failed in down bending. An examination of the engine revealed no anomalies. The accident pilot was experienced in the accident airplane and had built the airplane from a kit.

Text from the NTSB. Open the NTSB docket for CEN10FA042 for the full record.