What happened
During a cross-country flight, an instrument-rated pilot, a pilot-rated passenger, and five additional passengers were flying a business jet when the aircraft entered cloud cover while executing a climbing right turn. Following this, the aircraft began a descent. Air traffic control (ATC) attempted to contact the pilot to verify the aircraft's altitude and heading. After an initial period of silence, the pilot responded to a second query from ATC, but the aircraft continued to perform a series of climbing right and left turns.
Following further unsuccessful contact attempts by ATC, the aircraft entered a rapid, descending left turn and struck a shallow reservoir at high speed. The accident resulted in seven fatalities. Post-accident investigations of the engines and wreckage showed no mechanical failures that would have prevented the aircraft from operating normally.
Findings
Flight track data indicated that after departing the clouds, the aircraft performed multiple heading changes and altitude fluctuations before entering a steep, descending left turn. Investigators determined that the flight profile was consistent with somatogravic illusion, a form of spatial disorientation. It is believed that accelerations from increasing airspeed were misinterpreted by the pilot as a pitch-up motion, even though the aircraft was actually descending.
This disorientation likely led to an increased workload, preventing the pilot from effectively utilizing flight instruments to recover from the unusual attitude. While traces of ethanol and n-butanol were found in the tissues of the pilot and the pilot-rated passenger, investigators concluded these were likely post-accident artifacts rather than a result of recent ingestion. There was no evidence that medical conditions or medication use contributed to the loss of control.