What happened
On November 6, 2009, a Zenith Aircraft Company Zodiac 601 XL experimental light sport airplane, N538CJ, crashed near Agnos, Arkansas. The aircraft departed Sharp County Regional Airport (KCVK) at 0848 central standard time for a cross-country flight.
Data recovered from a handheld GPS unit showed the aircraft flying between 2,500 and 3,500 feet at airspeeds ranging from 60 to 108 knots. The flight included various maneuvers and a landing approach/pass at Horseshoe Bend Airport (K6M2). At the time of the accident, the aircraft was climbing at approximately 500 feet per minute through 2,800 feet and had accelerated to 100 knots.
Following an in-flight breakup, the aircraft impacted terrain, and the wreckage was scattered over a 600-foot area. The pilot was fatally injured.
The investigation
Investigators examined the wreckage, which included the fuselage, engine, propeller, and separated wing components. The right wing assembly was found in a pond, while the left wing, left wing spar, and left fuel tank were located elsewhere in the debris field. The engine and propeller remained attached to the fuselage, which rested inverted.
Structural analysis of the wings revealed compression buckling on both the upper and lower flanges of the rear spars. The damage to the wing skins and the upward and downward bending of the trailing edges were consistent with aerodynamic loads. Specifically, the investigators found that the outboard sections of the wings acted as large aileron-type surfaces, introducing significant lift load excursions.
An examination of the flap control assembly revealed a loose condition between the motor control arm and the left flap control arm. Additionally, the investigation noted that the ailerons lacked counterbalances, a known mitigation strategy for flutter. The engine and propeller showed no anomalies.