Flight and Accident Sequence
A non-instrument-rated pilot departed on a cross-country flight. Radar track data showed the airplane traveled a relatively straight course northeast for about 32 minutes. Near the end of the track, the airplane executed an increasingly tight left spiraling turn near the accident site. The airplane subsequently impacted steep sloping terrain, and a postimpact fire ensued. The impact segmented the airplane into several sections.
Wreckage Examination
Examination of the wreckage revealed no evidence of mechanical malfunction or failures that would have precluded normal operation. The attitude indicator was disassembled, and the vacuum-powered rotor and housing exhibited rotational scoring damage, indicating the instrument's vacuum system was operational at the time of the accident.
Weather Information
The investigation found no evidence that the pilot checked the weather or received weather information before departure. Surrounding weather reporting stations near the accident site reported winds with peak gusts up to 47 knots around the time of the accident. The pilot likely encountered mountain wave activity with severe turbulence, which resulted in loss of control of the airplane and impact with terrain.
Pilot Toxicology
Postmortem toxicology testing of the pilot's lung and muscle tissue samples detected several substances that are mentally and physically impairing individually and even more so in combination for performing hazardous and complex tasks. However, blood concentrations are needed to determine the level of impairment, and no blood samples were available. While the pilot was taking potentially impairing medications and likely had conditions that would influence decision making and reduce performance, without blood concentrations it was not possible to determine whether the combination of medications degraded his ability to safely operate the airplane.
Probable Cause
The National Transportation Safety Board determined that the probable cause of this accident was the pilot's encounter with mountain wave activity with severe turbulence, which resulted in a loss of airplane control. Contributing to the accident was the pilot's failure to obtain a preflight weather briefing.