Air Tractor AT-502 accident near Chowchilla, California, August 5, 2006

The NTSB's narrative final · quoted from the NTSB record

Near the end of an aerial application flight, the pilot maneuvered the airplane 1/3-mile northwest of the designated field and began reversing course. A flagger in the field reported observing the airplane's main light turn on, which was unusual because the airplane was neither over a designated spray field nor an airstrip. Thereafter, the airplane rolled completely inverted and impacted the ground. About 6 weeks earlier, the pilot had experienced pain related to the presence of a kidney stone. He reported pain in his abdominal area, in his right flank, and above his hip. The pilot was taken to the hospital and was diagnosed as having 2 kidney stones; one in the ureter and one nearer the kidney. Days later, the pilot passed 2 fragments of the ureter stone; however, the one nearer the kidney was likely still there. When the pilot reported for work on the morning of the accident day, company personnel observed him rubbing his sides above his hip, indicative of the remaining stone inducing pain and discomfort. The pilot reported that he felt somewhat uncomfortable and he felt "some pain in his sides." The operator reported that the activation switch for the airplane's lights is located on the flight control stick. The operator simulated holding onto the control stick and doubling over. When these actions were performed, the airplane was capable of quickly rolling inverted. The pilot likely experienced a significant incapacitating event due to pain from the kidney stone, which resulted in his losing control of the airplane.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.