NTSB Probable Cause

CONTINUED FLIGHT BY THE PILOT INTO KNOWN ADVERSE WEATHER AND HIS EXCEEDING THE DESIGN STRESS LIMITS OF THE AIRCRAFT, WHICH RESULTED IN FAILURE OF THE WING SPARS AND SEPARATION OF THE RIGHT WING AND EMPENNAGE (STABILIZERS). CONTRIBUTING FACTORS WERE: CONTINUED FLIGHT BY THE PILOT ABOVE THE MANEUVERING SPEED (VA), HIS LACK OF FAMILIARITY WITH THE MAKE AND MODEL OF AIRCRAFT, AND THUNDERSTORMS.