Incident Sequence
During an instrument landing system (ILS) approach, the pilot was established on the localizer outside the final approach fix in visual meteorological conditions above clouds. An air traffic controller issued vectors away from the localizer course. The instructions included a left 90-degree turn, a descent, and a 180-degree right turn back toward the localizer. During the right turn and descent, the airplane continued turning with increasing bank and subsequently impacted the ground.
Contributing Factors
According to a pilot weather report and flight path data, the pilot entered clouds as he began the right turn toward the localizer. The combination of descending turns while entering instrument conditions was conducive to spatial disorientation. The heading changes issued by the controller were rapid, of large magnitude, and, in combination with a descent clearance, likely contributed to the pilot’s disorientation. Additionally, diphenhydramine, a drug that may impair mental and/or physical abilities, was found in the pilot’s toxicological test results. While the exact effect of the drug at the time of the accident could not be determined, it may have contributed to the development of spatial disorientation.
Probable Cause
The probable cause, as stated in the official findings, is the pilot’s spatial disorientation, which resulted in his loss of airplane control. Contributing to the pilot's spatial disorientation was the sequence and timing of the instructions issued by the air traffic controller. The pilot’s operation of the airplane after using impairing medication may also have contributed.