Flight and Witness Observations
The aircraft, equipped with dual controls, departed for a demonstration flight with a pilot in the front seat and a pilot-rated passenger in the back. The flight was intended to include only low-G maneuvers. An agricultural pilot reported seeing the aircraft in a shallow climb at about 500 feet above ground level (agl). An eyewitness located over a mile from the accident site heard an engine surging and looked up, observing a yellow aircraft flying straight and level at approximately 1,000 feet agl. As the witness watched, something fell from the aircraft, followed by a loud boom. The aircraft then pitched up, nosed over, rolled, and entered a spin that continued until impact.
Aircraft Weight and Configuration
The aircraft was designed for aerobatic maneuvers, and its maximum allowable gross weight for aerobatics was 1,550 pounds. At the time of the accident, the aircraft was estimated to weigh 1,639 pounds, exceeding the aerobatic weight limit. The aircraft had performed aerobatic maneuvers on previous flights since its manufacture.
Wing and Component Examination
The outboard portion of the left wing was found 0.17 miles from the main crash site. Examination of the main spar revealed evidence of a ductile fracture due to a positive overload. The spar material met design specifications for metal composition and hardness. No evidence of fatigue or corrosion was found. The outboard section of the left wing did not exhibit any evidence of aeroelastic divergence. A flutter test demonstrated that the aircraft design was free from flutter at speeds above its design envelope. Wing load testing showed that the wing design was capable of supporting a limit load of +6 G's and an ultimate load of +9 G's for 3 seconds without failure.
Engine Management System Data
The Engine Management System nonvolatile memory readout provided data points indicating the aircraft was traveling at 191 mph in level flight. The maneuvering speed under the same conditions was 142 mph.