What happened
During an instrument approach using LOC/DME procedures, an aircraft struck mountainous terrain roughly 10.5 dme from the airfield. At the time of the impact, the aircraft was in a landing configuration. Investigation of the wreckage revealed that the elevator trim jackscrew was positioned approximately 18 degrees in a nose-up attitude. The altitude preselect, which was integrated with the Sperry autopilot system, had been set to 9,500 feet. This setting matched the minimum descent altitude required until reaching the final approach fix, which is situated at 9.3 dme.
Findings
Investigators recovered twenty-four different prescription and nonprescription medications from the cabin. A toxicology analysis of the pilot's liver fluid revealed a concentration of 0.206 (ug/ml, ug/g) of chlorpheniramine, an antihistamine. An FAA flight surgeon estimated this level would correspond to roughly .034 ug/ml in the blood, which falls within the therapeutic range of .01 to .04 ug/ml. However, this specific medication is considered contraindicated for flight operations because it can induce drowsiness. This substance was a known component of Comtrex, one of the medications found on board. The accident resulted in six fatalities.
The pilot's impairment from antihistamine use contributed to an inadvertent stall while the autopilot was active during the approach.