Accident Sequence
The pilot was attempting a circling approach in strong gusty tailwind conditions. Radar data and air traffic controller reports confirmed that the airplane was circling at or below the minimum descent altitude of 720 feet (708 feet above ground level [agl]) while flying in and out of an overcast ceiling that varied between 600 feet and 1,100 feet agl. The airplane was traveling at 100 knots and was close to the runway threshold on the left downwind leg of the airport traffic pattern. To align with the runway, a 180-degree turn with a bank angle of 45 degrees or greater would have been required.
Stall Analysis
Assuming a consistent bank of 45 degrees and an estimated stall speed of 88 to 94 knots, the airplane would have been near stall during that turn. If the bank angle increased due to the tailwind, the stall speed would have risen above 100 knots. Witnesses observed the airplane descending out of the clouds in a nose-down attitude. The investigation concluded that it was likely the pilot encountered an aerodynamic stall while banking sharply, flying in and out of clouds, while trying to align the airplane with the runway.
Toxicological Examination
Toxicological testing detected the presence of zolpidem, a sleep aid marketed as Ambien, but at levels well below the therapeutic range. These levels were consistent with the pilot taking the medication the evening before the accident. Consequently, it was determined that the pilot was not impaired due to the zolpidem.
Mechanical Examination
An examination of the wreckage revealed no preimpact mechanical malfunctions.
Probable Cause
Probable cause was determined to be the pilot's failure to maintain airspeed while banking aggressively in and out of clouds for landing in gusty tailwind conditions, which resulted in an aerodynamic stall and uncontrolled descent.