ERA17FA131 · Air Tractor Inc AT 602

The nearly 30,000-hour commercial pilot was conducting an aerial application flight. A nearby witness heard the airplane and reported that it sounded normal, then about 10 to 15 seconds later, he heard a "pop" sound followed by an explosion. Examination of the accident site, which was located well within the typical agricultural turn distance location for a turbine-powered airplane, revealed that the left wing collided with trees in a wings-level attitude. The airplane was destroyed by impact and a postcrash fire. No preexisting mechanical anomalies were noted with the airplane or its systems that would have precluded normal operation and propeller damage indicated that the engine was producing power at the time of impact.

The pilot was reported by family members to have had a cold the day before the accident, and toxicology identified doxylamine, a sedating antihistamine, in the pilot's blood and urine. The pilot may have experienced impairing effects from the doxylamine, which could have affected his reaction time, sleepiness, and judgment. Although the autopsy did not identify any incapacitating medical conditions, there are a number of conditions that could incapacitate a pilot and leave no evidence at autopsy. The airplane's descent below the height of trees, the pilot's failure to avoid trees before impact, and his failure to use a nearby open field as a forced landing site suggest that he likely was unable to perform basic piloting functions, most likely due to incapacitation, although the reason for incapacitation could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset