Preflight and Departure
Before departure from an airport designated as GAD, the pilot obtained a preflight weather briefing that included Convective SIGMET information. During the briefing, he acknowledged to the briefer that he was aware of thunderstorm activity northeast of GAD. The pilot then departed GAD and proceeded northeast toward SME.
In-Flight Weather Encounter
While in cruise flight north of an area designated CSV, the pilot requested to deviate to the left of course for what he described as an "immediate buildup." The controller cleared the pilot to deviate either right or left as necessary. A study of weather echo data and ATC radar data, correlated to the airplane's ground track, indicated that at the time of the request, the airplane was likely encountering the southern edge of an intense weather echo.
After the pilot acknowledged the clearance, the controller advised the pilot that there appeared to be "weather" off the pilot's left side. The pilot responded that he also saw weather in front and that he wanted to continue turning left to avoid it. The controller then stated that he did not see any weather for which the pilot would need to deviate to the left, and again cleared the pilot to deviate either right or left.
Subsequent Clearance and Conditions
About one minute later, the controller restricted the pilot's heading and altitude clearances, and the pilot acknowledged. The controller did not provide the pilot with information on echo intensity, location, or distance. The pilot did not request any further deviations or advise of an emergency.
Weather and Wreckage Examination
According to the weather echo and ground track study, the airplane encountered intense to extreme thunderstorm activity and turbulence. Examination of the wreckage revealed no evidence of mechanical malfunction.