HISTORY OF FLIGHTOn June 8, 2024, about 0721 mountain standard time (MST), an experimental amateur-built Rans S-12XL Airaile airplane, N518D, was substantially damaged when it was involved in an accident near Picacho Peak, Arizona. The pilot sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to witnesses, on the morning of the accident the pilot departed La Cholla Airpark, Tucson, Arizona, about 0700 and flew northwest about 23 nm 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.” The airplane subsequently impacted the northwest side of the mountain, about 81 ft below the summit. Video evidence was provided by a passenger of a previous flight with the pilot; this pilot-rated passenger described the flight as their normal practice of “buzzing the hikers” as they have been doing for the last 16 years. The cellphone video footage begins with the airplane inflight just southwest of, and above, the summit, orbiting clockwise. The flight path continued north; the airplane flew west to east over the ridgeline and established a flight path from north to south. While flying south, the airplane converged with the ridgeline and flew over the summit at a low altitude. An instrument-rated private pilot who had previously flown with the accident pilot as a passenger 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 passenger was comfortable with and the passenger subsequently asked the accident pilot to return to the airport. PERSONNEL INFORMATIONOne pilot logbook was provided during this investigation. Although the pilot’s daughter reported that he obtained his sport pilot license around 2008, the first date indicating pilot experience in the logbook was July 3, 2023, and the last entry was May 4, 2024. Each flight identified in the pilot’s log was conducted in the accident airplane, and the total flight experience indicated in this logbook was 1,396.9 hours. The date of the pilot’s last flight review was October 29, 2023 and the logbook also indicated two biennial flights were conducted on October 25, 2023; the remarks section indicated that a biennial flight review was conducted, and a certificated flight instructor’s (CFI) signature was present. The second flight indicated that the check ride was conducted with the same CFI; however, no signature was annotated. AIRCRAFT INFORMATIONAccording to maintenance logbook entries, the experimental, amateur-built airplane had an “annual inspection” on June 7, 2023. Since that inspection, the logbook entries showed that the pilot changed the oil and oil filter, changed the spark plugs, and cleaned the air filters on August 9, 2023. Additionally, a no-start condition was identified due to incorrect wiring of the ignition coils to the capacitor distribution ignition boxes, and was rectified on April 28, 2024. The last logbook entry showed that mechanical synchronization of both carburetors was performed on June 7, 2024. The logbook indicated that on March 4, 2022, the engine, propeller and airframe total times were identical at 1,239.7 hours. At the accident site, the Hobbs meter indicated 1,495.5 hours. METEOROLOGICAL INFORMATIONAccording to interpolated High Resolution Rapid Refresh (HRRR) model wind data near the accident location, valid for 0700 MST on the day of the accident, at 3,250 ft above mean sea level (msl) the wind was from 204° at 9 knots and the temperature was 27.9° F. At 3,500 ft msl the wind was from 220° at 8 knots and the temperature was 27.5° F. The KIWA WSR-88D NEXRAD Doppler weather radar was located about 40 miles to the north-northwest of the accident site at an elevation of about 1,400 feet. A Velocity Azimuth Display profile of the wind above the radar indicated that about the time of the accident, at 2,000 ft msl, the wind was from the southeast 10 knots; at 3,000 ft msl the wind was from the south at 10 knots, and at 4,000 ft msl the wind was from the southwest at 5 knots. Forecast wind barbs for the accident region valid for 0700 mst on the day of the accident were retrieved from the Aviation Weather Center. Forecast wind barbs depicted the wind conditions at 3,000 ft agl indicated that the wind direction for the local area and at the accident site was from the southwest between 10 knots – 15 knots. The wreckage was located at an altitude about 1,558 ft above the desert floor (3,358 ft msl). About the time of the accident, the density altitude at the wreckage site was 5,590 ft. The base of the Picacho Peak mountain range began in the northwest and continued about 1.5 miles to the southwest, where it reached its summit. The FAA Aviation Weather Handbook (FAA-H-8083-28B) defines turbulence as the irregular motion of an aircraft in flight, especially when characterized by rapid up-and-down motion caused by a rapid variation of atmospheric wind velocities. Turbulence is caused by convective currents (called convective turbulence), obstructions in the wind flow (called mechanical turbulence), and wind shear. The effect of turbulence varies based on the size of the aircraft. Light turbulence causes slight, erratic changes in altitude and/or attitude (pitch, roll, or yaw). When the air is too dry for cumuliform clouds to form, convective currents can still be active. This is called dry convection, or thermals. A pilot has little or no indication of their presence until encountering the turbulence. Section 19.2.2 of this handbook identified mechanical turbulence as turbulence caused by obstructions to the wind flow, such as trees, buildings, mountains, and so on. The handbook stated the following: Obstructions to the wind flow disrupt smooth wind flow into a complex snarl of eddies. An aircraft flying through these eddies experiences mechanical turbulence. The intensity of mechanical turbulence depends on wind speed and roughness of the obstructions. The higher the speed and/or the rougher the surface, the greater the turbulence. The wind carries the turbulent eddies downstream, with the distance dependent on wind speed and stability of the air. Unstable air allows larger eddies to form rather than those that form in stable air; but the instability breaks up the eddies quickly, while in stable air they dissipate slowly. Section 19.2.5.3 of this handbook identified turbulence associated with low-level mountain flying. The handbook stated the following: Mountain flying literature often cite 20 kt as the criterion for classifying a wind as “strong.” This criterion refers to the large-scale (or prevailing wind in the area as opposed to a local wind gust) wind speed at the crest of the ridge or level of the mountain peaks, upwind of the aircraft’s position. Such an ambient wind flow perpendicular to a ridge will lead to substantially stronger surface winds, with the likelihood of turbulence. Similar wind enhancements can be anticipated near the slopes of an isolated peak. This effect on the aircraft can be exacerbated by loss of aircraft performance because of the high-density altitude. AIRPORT INFORMATIONAccording to maintenance logbook entries, the experimental, amateur-built airplane had an “annual inspection” on June 7, 2023. Since that inspection, the logbook entries showed that the pilot changed the oil and oil filter, changed the spark plugs, and cleaned the air filters on August 9, 2023. Additionally, a no-start condition was identified due to incorrect wiring of the ignition coils to the capacitor distribution ignition boxes, and was rectified on April 28, 2024. The last logbook entry showed that mechanical synchronization of both carburetors was performed on June 7, 2024. The logbook indicated that on March 4, 2022, the engine, propeller and airframe total times were identical at 1,239.7 hours. At the accident site, the Hobbs meter indicated 1,495.5 hours. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted steep mountainous terrain in a nose-down attitude, remained localized within the impact crater, and came to rest in a left-wing-low attitude at an elevation of 3,358 ft msl. The right wing root above the forward fuselage remained in the impact crater and the left wing was pinned to the ground and prevented the airplane from falling off the cliff about 22 ft to the northwest. The nose of the airplane and forward fuselage were crushed aft. The cockpit showed upward and aft crushing with uninhabitable structural encroachment. The right wing exhibited aft crushing signatures to the outboard wing structure and attached aileron. The right wing from mid-span to wing root exhibited accordion-like folding signatures at the trailing edge including the flap, with impact damage to the leading edge and wing lift strut. The left wing sustained impact damage to the outboard section to about mid-span from the leading to trailing edge with the flap and aileron attached. The tailcone remained attached to the lower aft fuselage and the empennage was unremarkable. Flight control continuity was established from the cockpit to each of the primary flight control surfaces. The fuel tank was breached, but a witness who checked the pilot’s vital signs noticed a strong odor of fuel at the site. The engine remained attached to the aft fuselage. The engine remained attached to the aft fuselage with impact damage observed to the 1/3 carburetor (the carburetor serving cylinder Nos. 1 and 3) and the engine coolant system. A postaccident examination and engine functional test run were accomplished. To facilitate the engine test run, the 1/3 carburetor was secured to the intake manifold and the coolant system was bypassed. During the test run, the engine started and idled without anomaly. The throttle was advanced and a corresponding increase in RPM was observed. The engine was shut down to cool, and a second functional test run revealed no preimpact malfunctions or anomalies that would have prevented normal operation. Each of the propeller blades were fracture-separated evenly about 12 inches from their respective blade roots. The spinner sustained minor impact damage. . MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy of the pilot was performed by the Pinal County Medical Examiner’s Office. According to the autopsy report, the cause of death was multiple blunt force trauma, and the manner of death was accident. According to the pilot's autopsy report and accompanying clinical history, he had heart disease including moderate-to-severe coronary artery disease with prior heart attack, stenting, and cardiomyopathy. The autopsy did not identify specific evidence that an impairing or incapacitating cardiovascular event occurred, but such an event cannot be excluded by autopsy evidence alone. The pilot's documented medical history also included obstructive sleep apnea. Postmortem toxicology testing performed at the FAA Forensic Sciences Laboratory found Ethanol, Propanol (N-), Glucose, Hemoglobin A1c, Diphenhydramine, Acetaminophen, Loratadine, Desloratadine, Tamsulosin, Atorvastatin, Valsartan, Carvedilol, Sacubitril, and Desethyl Sacubitril in the pilot’s blood and/or urine. The FAA laboratory detected ethanol at a low level in cavity blood, along with n-propanol, with negative ethanol and n-propanol testing of urine and vitreous fluid. National Medical Services Labs detected ethanol at a low level in pleural cavity blood. Urine glucose was abnormally elevated, but vitreous glucose was not, and hemoglobin A1c (a marker of average blood glucose over the prior few months) was normal. Pertinent findings included evidence of use of the sedating antihistamine diphenhydramine. The diphenhydramine level measured in postmortem cavity blood cannot 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. Acetaminophen is an over-the-counter medication commonly used to treat minor aches and pains and reduce fever. Acetaminophen is not generally considered impairing. Tamsulosin (Flomax) is an alpha blocker used to treat benign prostate hyperplasia and is acceptable for pilots. Loratadine (Claritin) and the metabolite Desloratadine are non-prescription non-sedating antihistamine used to treat allergies. Loratadine is acceptable for pilots. Carvedilol (Coreg) is a beta-blocker used to treat high blood pressure and is acceptable for pilots. Sacubitril is a prescription medication available as a combination drug with valsartan, which was also detected in this case. This combination drug is used in the treatment of chronic heart failure. Desethyl sacubitril is a metabolite of sacubitril. Sacubitril is not typically impairing.