ERA16FA006

The pilot's decision to fly into a known area of adverse weather, which resulted in the airplane entering a severe thunderstorm and a subsequent loss of control.

The instrument-rated private pilot was on an instrument flight rules (IFR) cross-country flight; while en route, the pilot elected to divert to an intermediate airport to "check the weather." The pilot was subsequently provided a weather briefing that described a line of convective weather along the intended route of flight. The airplane departed about 45 minutes later and flew east along the south side of an east-west line of thunderstorms. The pilot was communicating with air traffic control, and when asked by the air traffic controller if he had onboard weather information, the pilot stated that he had NEXRAD. The airplane was equipped with satellite-delivered weather information service that was displayed in the cockpit, and it is likely that the pilot was referring to NEXRAD images provided by that system.  The pilot requested and was granted permission to turn north in order to navigate through the line of storms toward his destination. Ground track and weather radar data revealed that the airplane penetrated a thunderstorm cell of strong intensity The pilot subsequently lost control of the airplane before it rapidly descended to ground impact. The wreckage debris path was compact, and examination of the wreckage revealed extensive fragmentation and thermal damage. No preimpact mechanical malfunctions were noted that would have precluded normal operation of the airplane. The impact damage to the engine and propeller were consistent with the engine operating at a high power setting at the time of impact. The satellite-delivered weather information likely being used by the pilot did not provide real-time weather radar images in the cockpit, with a delay between the time the weather was observed and when it was provided. It is likely that the pilot attempted to maneuver through the line of thunderstorms, but the time delay in the satellite-delivered weather data likely resulted in inadvertent penetration of a severe thunderstorm cell. The investigation could not determine the color intensity of the precipitation being displayed to the pilot on cockpit avionics around the time of the accident. However, the most extreme color band that could have been shown would have been dark orange, which was classified as 55 dBZ. On the WSR-88D and satellite-delivered radar images, orange was classified as 40 dBZ. The WSR-88D Level 2 reflectivity product revealed that the weather reflectivity, around the accident location, ranged from 5 dBZ to 55 dBZ. Postaccident toxicology testing revealed the presence of citalopram, an antidepressant medication, and ethanol. Citalopram is one of four medications that has been approved by the FAA for the treatment of depression. Personal medical records documented that the pilot's depression was well controlled with citalopram, and the pilot had no adverse effects from the medication. Therefore, there is no evidence that depression or the citalopram impaired the pilot's decision-making ability or his ability to safely operate the airplane. The ethanol detected was likely from postmortem production. Further, considering that the level of the ethanol was below a level that would be considered impairing, the ethanol detected did not impair the pilot nor contribute to the accident.

The Quillen College of Medicine, East Tennessee State University, Division of Forensic Pathology, performed an autopsy on the pilot. The report listed the cause of death as "multiple blunt force injuries." Toxicological testing on the pilot's muscle tissue was performed at the FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. TheFAA Bioaeronautical Research Sciences Laboratory toxicology testing was limited by the absence of available blood or body fluids; only muscle tissue was available. Testing detected 0.01 g/dl of ethanol as well as citalopram and its metabolite N-desmethylcitalopram in muscle. According to the FAA, ethanol is a powerful central nervous system depressant that distributes evenly throughout tissues based on the water content of that tissue. In the United States, a blood level of 0.08 g/dl is considered impairing, and current laws prohibit operating a motor vehicle at this level but impairment has been documented at levels as low as 0.02 g/dl. Ethanol may also be produced in the body after death by microbial activity. Citalopram is a prescription antidepressant also named Celexa. The pilot's medical records documented that the pilot's depression had improved significantly on citalopram, and his personal physician noted on the last visit on July 14, 2015, the pilot was doing well on medication, had no significant depressive symptoms, no difficulty concentrating, and no suicidal thoughts or wishes. According to the FAA's Guide for Aviation Medical Examiners, pilots treated for depression with citalopram may be considered for special issuance of a medical certificate if the pilot has been clinically stable as well as on a stable dose of medication without any aeromedically significant side effects and/or an increase in symptoms. For further information, reference the NTSB Medical Officer's Factual Report in the public docket for with this investigation. The 1937 special recorded weather observation at Tri-Cities Regional Airport (TRI), Bristol, Tennessee, located about 13 miles to the northwest of the accident location, included variable wind at 3 knots, visibility 6 miles due to thunderstorms and rain, scattered cumulonimbus clouds at 2,300 ft above ground level (agl), broken at 6,000 feet agl, overcast at 11,000 feet agl, temperature 19°C, dew point 17°C, and barometric altimeter 30.05 inches of mercury. The remarks section of the special weather observation stated that a thunderstorm began at 1931 with occasional lighting in cloud and cloud to ground at the airport. The thunderstorms in the vicinity were moving east. The 1915 recorded weather observation at Elizabethton Airport (0A9), Elizabethton, Tennessee, located about 10 miles to the northeast of the accident location, included calm winds, 10 miles visibility, few clouds at 6,000 feet agl, scattered clouds at 7,500 feet agl, broken clouds at 9,000 feet agl, and barometric altimeter 30.03 inches of mercury. Weather radar data indicated that the line of convectively contained cells from 5 dBZ (decibels of equivalent reflectivity) to greater than 55dBZ, and the weather cell around the time and vicinity of the accident indicated greater than 55 dBZ. At 1855, a convective SIGMET was issued advising of a line of thunderstorms 50 miles wide along a line that went through the accident region. The line was reported to be moving from 260° at 30 knots, with cloud tops to FL440 (44,000 feet msl). Lightning data between 1900 and the time of the accident for the area surrounding the accident location showed lightning activity in the area; however, there was no lightning activity associated with the cell that coincided with the location of the airplane at the time of the accident. Figure 1: KRMX Reflectivity Product initiated at 1915, White Line was Accident Flight Path at 1917 Geostationary Operational Environmental Satellite (GOES)-13 infrared cloud-top temperatures varied between about -20°C and -53°C in the accident region, corresponding to heights of about 22,600 ft msl and greater than 35,000 ft msl, respectively. According to the United States Naval Observatory, official sunset was at 1902, and the end of civil twilight was at 1923. Moonset occurred at 1725, and 10% of the moon disc would have been visible had the moon been above the horizon. According to Federal Aviation Administration (FAA) records, the pilot, age 45, held a private pilot certificate with airplane single-engine land and instrument airplane ratings, which was issued December 28, 2013. He held an FAA third-class medical certificate, issued April 18, 2014, with a limitation that he "must wear corrective lenses." At the time of the medical examination, the pilot reported 279 total hours of flight experience with 73.9 hours in the previous 6 months. At the time of this writing, no pilot logbooks were provided to the. The airplane wreckage was found in the Cherokee National Forest, in the vicinity of the accident flight's last radar return, at an elevation of 2,825 ft msl. The slope around the accident site varied between 20° and 30°. The airplane impacted two 27-ft-tall trees. The debris path was fairly compact, and a considerable amount of debris was located within an impact crater that was about the length of the airplane's wingspan. The airframe was impact-damaged, segmented, and thermally destroyed. The engine was found in a 4-ft-deep crater and remained attached to the firewall. The engine mounts were impact-separated and were located with the main wreckage. The propeller was impact-separated at the crankshaft propeller flange. The attitude indicator was located within the debris field; it exhibited impact damage and displayed a nose-down, inverted right-wing-low attitude. No other instruments were readable. The nose landing gear wheel was impact-separated and located about 45 ft downhill from the main wreckage. The nose landing gear strut was impacted-separated and was located in the impact crater. The main wing spar was located in the impact crater. It was composed of composite material, was thermally destroyed, and exhibited some impact splintering. Left Wing The left wing was thermally destroyed. The left wing navigation light was located at one end of the impact crater. The left wing speed brake was found in the stowed position. The left main wheel assembly was impact-separated. The aileron and flap were thermally destroyed, and an accurate flap position could not be conclusively determined. Right Wing The right wing was thermally destroyed. The right wing navigation light was located at the opposite end of the impact crater from the left wing navigation light. The right wing speed brake was found in the stowed position. The right main wheel assembly was thermally destroyed. The aileron and flap were thermally destroyed, and an accurate flap position could not be conclusively determined. Empennage The empennage assembly, which included the vertical and horizontal stabilizers, was thermally damaged. The rudder remained attached to the vertical stabilizer but exhibited thermal damage on its leading edge. The rudder cables remained attached to their respective rudder horns. Engine The engine remained attached to the firewall, which had become impact separated from the airframe. The engine was an TSIO-550- C, 310-hp. The propeller was separated at the propeller flange. The No. 6 cylinder was impact separated from the engine. The oil pan was thermally damaged. The camshaft was visible, and all of the connecting rods were visible and remained attached to the crankshaft. The crankshaft exhibited torsional twist, 45° lip faces, and radial cracking. The fuel pump was thermally destroyed. The fuel manifold valve was impact separated; it was disassembled and found to contain soot and debris but was otherwise unremarkable. The magnetos were impact separated, fragmented, and thermally destroyed. The oil pump was impact da