the pilot's impairment of judgment and performance due to a drug (cocaine); his improper in-flight decision to continue flight over an overcast condition and then to descend into instrument meteorological conditions (IMC); his failure to maintain control of the airplane, due to spatial disorientation, after entering clouds; and his exceeding the design/stress limits of the airplane. Factors relating to the accident were: the weather conditions, the pilot's lack of instrument experience, and the pilot's overconfidence in his personal ability.