Amateur-built VANS RV-9A N559B accident near May, Idaho

Probable cause

The pilot's failure to maintain control of the airplane during maneuvering flight due to spatial disorientation. Contributing to the accident was the pilot's ingestion of an impairing level of over-the-counter medication.

NTSB analysis

While approaching his destination airport, the pilot made a left turn to circle over an adjacent town. He then reduced his angle of bank, but continued in a left turn so as to overfly and evaluate the surface condition of the dirt/turf airstrip where he planned to land. At the time that he ultimately rolled wings-level to parallel the runway, he had been in a left turn for approximately four minutes. About 20 seconds after the pilot rolled out of the turn, the airplane rolled to the left and descended into the terrain. A forensic toxicology examination determined that the pilot's blood contained levels of an over-the-counter sedating antihistamine that would be expected to result in impairment, and it is likely that the pilot lost control of his airplane due to spatial disorientation exacerbated by the effects of the antihistamine. A postaccident examination of the airplane's flight control system and primary structure performed by a Federal Aviation Administration airworthiness inspector did not reveal any evidence of a malfunction or anomaly that would have contributed to the rapid roll and descent into the terrain.

Text from the NTSB. Open the NTSB docket for WPR10LA299 for the full record.