Amateur-built S-12XL Airaile N518D accident near Picacho Peak, Arizona

Probable cause

The pilot’s decision to conduct a low-altitude flight in mountainous terrain and his subsequent loss of airplane control after encountering mechanical turbulence, which resulted in an impact with the terrain.

NTSB analysis

The pilot departed and flew to the area of Picacho Peak State Park, Arizona. Witnesses hiking near the accident site reported that the airplane was flying “dangerously close to the mountain” and subsequently impacted it’s the north side, about 81 ft below the summit. Meteorological conditions near the accident site about the time of the accident indicated that the wind was likely from the southwest at about 10 knots, gusting to 15 knots at the surface. Additionally, a 50° windshear was present with minimal change in magnitude between 3,000 to 4,000 ft msl. The density altitude at the time of the accident was 5,590 ft.

Cell phone video of a previous flight conducted by the accident pilot was provided by a pilot-rated passenger who flew with the pilot on several occasions. This person indicated that the recorded flight illustrated the pilot’s standard practice of “buzzing the hikers.” The video showed the pilot and passenger in the accident airplane, orbiting the peak in a clockwise manner. The pilot subsequently initiated a flight path from north to south while converging on the north side of the ridgeline and flying over the summit at a low altitude.

Another pilot-rated passenger who had previously flown with the pilot reported that during their flight, the accident pilot mentioned his interest in flying low to the ground, allowing him to interact with people or spot wildlife. During their flight, the pilot descended lower than the pilot-rated passenger was comfortable with and the passenger subsequently asked the accident pilot to return to the airport.

The flight path in the video footage showed the pilot operating the airplane on a flight track that converged with the ridgeline just above the summit. The pilot’s standard practice of flying at low altitude above the summit would have subjected the airplane to mechanical turbulence perpendicular to the airplane’s direction of flight. The mechanical turbulence encountered by the airplane while converging on the summit at low altitude likely resulted in the pilot’s loss of control, resulting in the airplane’s subsequent impact with terrain just below the summit.

Toxicology testing indicated evidence of the pilot’s use of the sedating antihistamine diphenhydramine. The diphenhydramine level measured in postmortem cavity blood could not be reliably compared to reference ranges in living individuals but indicated a possibility that the pilot might have been experiencing related drowsiness or cognitive/psychomotor slowing at the time of the accident. The pilot also had heart disease and a documented history of obstructive sleep apnea. Overall, the medical and toxicological evidence in this case indicated an increased risk of medical impairment but did not establish that impairment contributed to the accident.

Text from the NTSB. Open the NTSB docket for WPR24FA185 for the full record.