Flight History
The pilot received a preflight weather briefing warning of thunderstorms with tops reaching 45,000 feet along the intended route. En route, air traffic control advised of significant areas of heavy precipitation. The pilot responded, "uh roger one nine whiskey it looks like on our radar here that uh we go straight ahead we'll be all right there." The flight was cleared to descend to 11,000 feet, and the pilot requested a deviation to the right for weather avoidance.
Weather Conditions
The pilot conducted several routine radio communications while descending at an average rate of approximately 2,571 feet per minute. During this descent, the calculated calibrated airspeed increased from about 190 knots to approximately 265 knots—the design dive speed (Vd). The flight subsequently encountered a level 5 weather echo, after which it began a high rate of descent.
Accident Sequence
Post-accident examination revealed that both horizontal stabilizers with elevators and both outer portions of both wings failed in a downward direction. Investigators found no evidence of preimpact failure or malfunction in the flight control cables, fracture surfaces, engines, or propellers. The pilot did not request any pilot reports during the flight. The airplane's design maneuvering speed (Va) was 169 knots indicated; the Pilot's Operating Handbook (POH) directs pilots to reduce speed to Va for turbulence penetration.
Probable Cause
The official probable cause was the poor in-flight weather evaluation by the pilot-in-command and his operation of the airplane at an indicated airspeed greater than the design maneuvering speed (Va) in a thunderstorm, contrary to the POH, resulting in an in-flight breakup. A contributing factor was the pilot's failure to obtain in-flight weather advisories from air traffic control before encountering the adverse weather.