Accident Sequence
While deviating around areas of low-intensity weather returns during climbout, the airplane passed through 20,500 feet and departed controlled flight, entering a right spiral. The descent rate exceeded 16,600 feet per minute between 18,300 and 3,900 feet, after which the rate slowed. Witnesses reported observing the airplane descending from the clouds in a right flap spin.
Wreckage and Impact
The empennage separated from the airplane in multiple pieces. Wreckage was scattered over an area up to 1.5 miles from the primary impact point. Both wings remained attached to the fuselage. The right engine was flamed out, and its propeller was found in the feathered position. No mechanical reason for the engine flameout could be determined.
Weather and Toxicology
A National Transportation Safety Board weather study indicated that moderate turbulence was present in the area. Toxicology tests on the pilot detected 0.151 micrograms per milliliter of chlorpheniramine in the blood; the normal therapeutic concentration ranges from 0.01 to 0.04. The effects of such an overdose include sedation, diminished mental alertness, and possible cardiovascular collapse or stimulation. The pilot, who was the sole occupant, did not indicate any difficulties during the flight.
Probable Cause
The probable cause of the accident was the pilot's failure to maintain control of the airplane, which resulted in an inadvertent spiral and subsequent rapid descent. The design stress limits of the airframe were exceeded, leading to an overload failure of the empennage. Factors contributing to the accident were turbulence and the pilot's physical impairment due to drugs.