What happened
On June 19, 2010, an experimental Oliver RV-9A, registration N559B, crashed approximately one-quarter mile south of May Airport in May, Idaho. The flight, which departed from Challis, Idaho, about 15 minutes prior to the accident, was being conducted under visual meteorological conditions with 10 miles of visibility. No flight plan had been in place.
The pilot was returning from a backcountry aerial camping trip. After a stop in Challis, the pilot began maneuvering over the May Airport area to evaluate the roughness of the dirt and turf landing surface. Witnesses on the ground observed the pilot flying over the airfield; they noted that the aircraft appeared to slow down before suddenly rolling to the left and entering a one-half turn spin into the ground. There were no reported audible changes in engine power or sounds indicating engine failure.
Data recovered from a Garmin 696 GPS unit showed that the pilot performed a series of turns over the town of May. The flight path included a shallow left turn, followed by a tighter turn with a diameter of approximately one-third mile, and finally a shallower left turn with a diameter of about three-quarters of a mile. After approximately four minutes of maneuvering, the pilot rolled the wings level to parallel the runway on an easterly heading. About 20 seconds after rolling out of the turn, the aircraft descended into the terrain. The GPS data indicated the aircraft was maintaining an airspeed between 81 and 83 miles per hour at the time of the descent.
The investigation
A Federal Aviation Administration (FAA) Airworthiness Inspector examined the flight control system and primary structure of the N559B and found no evidence of mechanical malfunction or anomaly that contributed to the roll and descent.
A forensic toxicological examination conducted by the FAA Civil Aerospace Medical Institute found 0.173 (ug/ml, ug/g) of Diphenhydramine in the pilot's blood and an undesignated level in the urine. Diphenhydramine is an over-the-counter antihistamine known to cause sedation, dizziness, and impaired coordination.
Findings
- The pilot failed to maintain control of the aircraft during maneuvering flight.
- The pilot's blood contained levels of an over-the-counter medication expected to cause impairment.
- The pilot likely experienced spatial disorientation exacerbated by the effects of the antihistamine.