Air Safety Institute Safety Spotlight
Summer is peak season for thunderstorms. As we take to the skies during the next few months, it's important to understand and respect the many hazards these storms can produce. The violent turbulence is only part of the story. Less dramatic but no less dangerous are the strong downdrafts, abrupt wind shear, and roiling gust front--especially when the pilot ignores warnings and launches directly toward the storm.
On January 11, 2005, the pilot of a Cessna T206H Stationair attempted to depart Huntsville International-Carl T. Jones Field in Alabama in the face of an approaching level-5 (now reported as "extreme") thunderstorm. The aircraft crashed into a wooded swamp about a mile east of the airport, killing the 1,400-hour, instrument-rated pilot and his passenger.
Shortly after 6 p.m., the pilot contacted the Huntsville ground controller and advised he was ready to taxi to Runway 18L. The controller said, "There's level-5 weather activity that is south of the airport moving to the northeast, so it's going to be crossing the runway south of the airport about three miles."
The controller suggested the pilot consider departing in the opposite direction, from Runway 36R, following a delay for inbound traffic. The pilot replied, "Uh, sir, we're ready to go at 18L. If we can go ahead and get it, and get vectors around [the weather]--if you could do that right off the end of the runway."
The controller agreed to coordinate the request. Two minutes later, the tower cleared the flight for takeoff and assigned the pilot a left turn to heading 090. Shortly after the Stationair departed, the tower controller attempted to contact the pilot but received no reply.
Radar data indicated the airplane climbed no higher than 300 feet agl. A witness near the south end of the runway saw the Stationair take off, turn left, and head due east with its wings level, but it was "too low" and "losing altitude quickly." The witness stated it was raining at the time with gusty winds.
An NTSB examination of the wreckage found no evidence of mechanical failure. The board determined that the accident's probable cause was the pilot's decision to attempt flight into known adverse weather.
Level-5 cells are intense thunderstorms typically associated with severe turbulence (up to 20 miles from the echo's edge), lightning, hail, and organized surface wind gusts. They can also cause microbursts--small but powerful downdrafts that can plunge to Earth at 6,000 feet per minute. These downdrafts spread outward in all directions upon reaching the surface, resulting in dangerous vertical and horizontal wind shear.
Attempting to fly in these conditions is a dangerous gamble. Better to shut down and try again after the weather moves on.
For more information, see the AOPA Air Safety Foundation's online thunderstorm resources.
An aviation technical writer for the AOPA Air Safety Foundation, Carl Peterson creates interactive courses and other safety education materials for the aviation community. He has been flying since 1989.
By Carl Peterson