WPR17FA120

The pilot's exceedance of the airplane's critical angle of attack while intentionally maneuvering in a steep bank at low altitude, which resulted in an accelerated aerodynamic stall and subsequent loss of control.

The commercial pilot and his son were conducting a personal flight. About 15 minutes after takeoff, the airplane flew a series of passes over a horse arena where the pilot's daughter was riding. The arena was situated within a geographic bowl depression, surrounded by hilly terrain and adjacent to three sets of power transmission lines. A pilot witness in an airplane flying above the accident airplane described the accident airplane's flight path as low and erratic, and a witness close to the arena described the initial pass as "aggressive." The pilot conducted the final pass over the arena at a much lower altitude than the previous passes. Multiple witnesses described the engine noise as "sputtering" and then going quiet either during the descent for the final pass, or just as the airplane flew over the arena. The engine sound then increased as the airplane climbed and entered a steep right bank, then descended into power lines and impacted the ground about 600 ft south of the arena. Calculations based on witness reports and impact geometry indicated that the radius of the turn before impact would have required a high angle of bank, resulting in an increase in stall speed, which would have led to an accelerated stall at an altitude too low for recovery. Examination revealed no anomalies with the airframe or engine that would have precluded normal operation, and damage signatures and witness accounts indicated that the engine was producing power at the time of the accident. Damage to the airplane's fuel tanks indicated that they contained fuel at the time of impact. The pilot's son, who was not a pilot, was seated in the front left seat. Since the airplane was equipped with dual controls, it could not be determined who was flying the airplane at the time of the accident. The pilot was familiar with the terrain in the area of the accident site. Witnesses stated that he had performed low passes there multiple times in the past and was aware of the power lines at the edge of the arena. The reduction in engine noise as reported by witnesses could have been the result of an actual loss of engine power or a power reduction made by the pilot to descend more rapidly in order to perform the pass at a lower altitude; however, if the pilot had been flying at an appropriate and safe altitude and the airplane had experienced a loss of engine power, it would have been within gliding distance of open terrain adequate for a forced landing. Given the pilot's previous behavior and the circumstances of the accident flight, it is likely that the pilot was performing an intentional, ostentatious display at low altitude when the accident occurred. Toxicology testing of the pilot indicated the presence of multiple impairing medications, as well as tetrahydrocannabinol carboxylic acid, a metabolite of tetrahydrocannabinol (THC), the active compound in marijuana. However, no blood was available for toxicology testing, and there is no known relationship between tissue levels and impairment. As a result, whether the pilot's use of multiple potentially impairing substances contributed to the accident could not be determined.

The Ventura County Medical Examiner's Office, Ventura, California, performed an autopsy of the pilot. The pilot's cause of death was multiple blunt force injuries. No significant natural disease was identified. The FAA's Bioaeronautical Sciences Research Laboratory performed toxicology testing on specimens of the pilot, which identified alprazolam and its metabolite, Alpha-hydroxyalprazolam; gabapentin; and tetrahydrocannabinol carboxylic acid, a metabolite of tetrahydrocannabinol (THC), the active compound in marijuana, in urine and liver tissue. THC was identified but not quantified in lung tissue, but testing of liver and kidney tissue for THC was inconclusive. Finally, ibuprofen was identified in urine. Alprazolam is a benzodiazepine available as a Schedule IV controlled substance via prescription used to treat anxiety and panic disorders and is commonly marketed with the name Xanax. It carries the warning, "Can cause paranoid or suicidal ideation and impair memory, judgment, and coordination. Combining with other substances, particularly alcohol, can slow breathing and possibly lead to death." Gabapentin is a prescription medication used to treat nerve pain and prevent seizures and is commonly marketed as Neurontin. Gabapentin increases the risk of suicidal thoughts and is a central nervous system (CNS) depressant. It carries the warning, "Patients should be advised that gabapentin may cause dizziness, somnolence, and other symptoms and signs of CNS depression." Both alprazolam and gabapentin are disqualifying for aeromedical certification. THC is the active component in marijuana, a Schedule I controlled substance; tetrahydrocannabinol carboxylic acid is an inactive metabolite. THC causes mood- altering effects, euphoria, and relaxation for a few hours after use. In research involving actual flying and/or use of flight simulators, impairment for up to 24 hours was noted following smoking marijuana. Of interest was the lack of pilot awareness of impairment or decreased performance in those studies. Ibuprofen is an over-the-counter analgesic often marketed with the names Advil and Motrin. It is not considered impairing. The pilot's personal medical records indicated that he visited a doctor after complaining of minor ailments including a cold, but there were no records indicating that he had been prescribed alprazolam or gabapentin. At 1555, the automated surface weather observation facility at CMA, elevation 65 ft mean sea level, reported wind from 250° at 5 knots, 10 miles visibility, temperature 70°F, dew point 61°F, and an altimeter setting of 29.86 inches of mercury. Using these values, the density altitude at the accident site was about 1,700 ft. Pilot The pilot, who was seated in the front right seat, held a commercial pilot certificate with ratings for airplane single-engine land and sea, airplane multiengine land, and instrument airplane. The pilot's most recent third-class FAA medical certificate was issued on January 28, 2016, with a requirement to have available glasses for near vision. He had reported no medical conditions and no medications on his application. No flight logbooks were recovered for the pilot. At the time of application for his medical certificate, he reported 1,989.9 total hours of flight experience, including 43.2 hours in the previous 6 months. One of the airplane's co-owners stated that, although the pilot did not own a share in the airplane, he started flying it about 3 years before the accident and typically flew it one or two times per week. He estimated that the pilot had about 500 hours of flight experience in the accident airplane make and model. Passenger The pilot's 15-year-old son was seated in the front left seat of the airplane. He did not hold a pilot certificate, although according to family members, he often sat in the left seat when flying with his father. His mother, who was divorced from the pilot, stated that she did not know they would be flying that day. She was aware that her son had previously flown in the airplane while seated in the front left seat. She further stated that she was never happy with the idea of her children flying with their father, and had been told that he had flown low over the accident site before, but after discussing the situation with legal counsel, concluded that there was nothing she could do to stop him from taking them. The airplane was manufactured in 1967 and was equipped with a Lycoming O-360-A4A engine, which was last overhauled in 1992. The most recent maintenance event was for an annual inspection, which was completed on February 1, 2017. At that time, the airframe had accrued 5,939.9 total flight hours, and the engine 1,796.4 hours since major overhaul. The airplane was equipped with dual cockpit flight controls. The airplane came to rest in the middle of a horse arena, which was 175 ft long and 85 ft wide, and oriented north-south. The arena was at an elevation of 590 ft msl and situated within a geographic bowl-like depression, flanked about 1/3 mile to the northwest by a 790-ft-tall hill, and by 1,030-ft-tall hills at a similar distance to the south and east. About 1,000 ft to the west of the arena, the terrain rose to about 770 ft, then gradually fell away through the Santa Rosa Valley before reaching CMA, 13 miles to the west. The Channel Islands were about 28 miles beyond CMA. The area surrounding the accident site was interspersed with hills, fields, and densely-populated housing developments. Open agricultural fields were located at an elevation of 625 ft about 1/2-mile northeast. Fields were also located at an elevation of 310 ft about 1 1/2 miles southwest. The arena was bordered to the east by three separate sets of power transmission lines oriented north-south. The lines were positioned about 60, 85, and 180 ft east of the arena edge. The closest two sets of lines were about 65 ft above ground level (agl), with the farthest line about 75 ft agl. The horse arena where the airplane crashed and the arena that the airplane initially overflew were separated by 50- to 80-ft-tall trees (See Figure 2). The first identified point of impact was a metallic 4-ft-long transfer mark on the power line closest to the arena (See Figure 3). The outboard right wingtip and aileron section was located about 30 ft south of the mark and exhibited striation marks on the wing leading edge, consistent with power line contact. Figure 2 - Accident Site Figure 3 - Accident Site with Power Transmission Lines in the Background The steel railings on the eastern edge of the arena were crushed and fragmented, and a fan of debris consisting of oil, the gascolator, and plexiglass and composite fragments extended on a heading of 250° toward the main wreckage. The airplane came to rest about 120 ft southwest of the initial power line impact point. The empennage was largely intact and upright. The forward cabin area had folded back over and under the aft cabin, leaving the wings inverted and the engine resting on the top side of the aft tailcone. The leading edges of both wings sustained crush damage along their entire length. A faint smell of aviation gasoline was present at the site by the time investigators arrived about 2 hours later. The airplane and engine were examined both at the accident site and 8 days later at a recovery facility. A complete examination report is contained within the public docket; the following is a summary of pertinent findings. The fuselage sustained extensive crush damage through to the tailcone. Both wings sustained leading edge crush damage about 90° relative to the direction of travel. Outboard of the fuel tanks, the damage displayed an accordion-like appearance. The wing tanks displayed bulging damage, consistent with hydraulic deformation, with both tanks breached at their outboard rib seams. The right wing remained attached and the left wing had compl