WPR18FA247

The pilot’s delayed recovery from an inadvertent spin and/or spiral dive and an exceedance of the glider’s design limit load during recovery, which resulted in an overload failure of both wings.

The two pilots onboard the motorized glider, one of whom was an owner of the glider, were participating in an informal competition, the goal of which was to fly between two predetermined locations in the shortest time. The takeoff, tow to altitude, and initial stages of the flight appeared uneventful. A low-resolution track of the glider’s flightpath indicated that the glider was likely flying around 14,500 ft mean sea level (msl) and circling in thermal lift just before the accident. A group of paraglider pilots was preparing to launch from an 8,700-ft-high bluff on the mountain over which the accident glider was circling. Their attention was drawn to the glider, which appeared to be performing a series of tight maneuvers that they described as “loops.” After a couple of “loops,” the glider’s wings began to flex upward almost vertically before one wing broke away and impacted the tail, and the glider descended to the ground. Ballistic trajectory analysis indicated that the glider likely broke up at about 11,500 ft msl while traveling in a steep descent toward the witnesses. Most of the glider was consumed by fire on impact, with only the separated portion of the left wing and a series of control surface, skin, and cabin components strewn over a 1,500-ft-long debris path escaping thermal damage. Although sections of the horizontal stabilizer broke away during the breakup, the horizontal stabilizer mount and elevator control structure remained attached to the glider at impact. Examination of the wreckage did not reveal any evidence of anomalies that would have precluded normal operation. Given that the purpose of the flight was a timed competition and that performing aerobatics would have been out of character for the pilot/owner, it is highly unlikely that the pilots were intentionally performing aerobatic loops as described by the paraglider pilots, particularly over a mountain ridge. Due to the witnesses’ location relative to the glider, it is more likely that the witnesses were observing the glider in either a spin or a spiral dive rather than a loop. The position of the sun, which would have been generally behind the glider and to the right relative to their position, would have presented it in a high-contrast environment and could also have hindered their frame of reference. G-loading calculations revealed that a loop of the radius and period observed by the witnesses was not physically possible because the glider would have been subject to stress significantly beyond its ultimate design limit load and would have experienced structural failure well before completion of the first maneuver. The published stall recovery technique requires that the pilot firmly ease the control stick forward and, if necessary, apply opposite rudder and aileron. With a more forward center of gravity, as was the case with the two occupants onboard, should the stall develop into a spin, the glider will enter a spiral dive after recovery, which is accompanied by a rapid increase in speed and acceleration that can quickly exceed limitations. The glider’s airbrakes can be extended at speeds approaching the never-exceed speed (Vne); however, damage to the left airbrake was consistent with an inflight separation, suggesting that the pilot had extended the airbrakes in an attempt to slow the glider and that the glider exceeded Vne. Excessive elevator control input during the attempted recovery from a high-speed dive would have resulted in the witness-observed upward bending of the wings and the subsequent failure of the wings due to overload. Such upward loading of the wings would not have been possible without the presence of the horizontal stabilizer and pilot input via the elevator. Evidence of electrical arcing was present in wiring that would only have been energized if the retractable engine was in transit. Those wires were protected by circuit breakers and the engine was stowed; therefore, the arcing was likely the result of an electrical short circuit that occurred on impact or as the glider broke apart in flight. Additionally, the glider’s FLARM collision avoidance system operated throughout the flight, further indicating that some form of electrical fire was unlikely. No evidence of bird strike was observed to any of the recovered components, and radar information revealed no evidence of any conflicting traffic in the immediate vicinity of the accident glider before the accident. The canopy was closed at impact; although both occupants were wearing parachutes, and one of them was not wearing the shoulder straps of his harness, there were no other obvious indications that they attempted to egress. Postaccident medical evaluation of the two pilots was limited due to the extent of injury. Whether a medical condition of either occupant contributed to the circumstances of the accident could not be determined. Given the lack of mechanical anomalies, the overload failure of the left wing, and the glider’s rapid descent before the accident, it is likely that the glider entered an inadvertent spin or spiral dive while maneuvering and that the pilot’s delayed recovery resulted in a rapid increase in speed. It is likely that, during recovery, the pilot either used excessive pitch control beyond the glider’s published maneuvering speed (Va) or the pilot exceeded the glider’s Vne during the subsequent steep descent.

Pilot Observations Pilots flying the task that day all reported good soaring conditions, including strong lift, good visibility, and minimal turbulence. Surface Analysis The National Weather Service (NWS) National Center for Environmental Prediction Surface Analysis Chart for 1400 depicted a general weak pressure gradient over the region with several thermal low-pressure systems to the northwest and southwest over California at 1005- and 1007-hectopscals (hPa) with a trough of low pressure extending between the lows. Additional thermal lows were also identified to the northeast over Idaho at 1012-hPa with a trough extending southwestward toward the accident site and to the southeast near the Nevada, California, and Arizona borders at 1004-hPa. No defined frontal boundaries were depicted over the western United States during the period. The station models surrounding the accident site depicted light winds, a few clouds to clear skies, with temperatures near 89°F, with a dew point temperature of 29°F. No significant weather was depicted surrounding the area of the accident site. Upper Air The NWS Storm Prediction Center forecast constant pressure charts for 700-hPa (approximately 10,000 ft) depicted an upper-level low-pressure system off the southern California coast with wind from the southeast at 5 knots in the vicinity of the accident site, with a temperature of 7ºC, and dew point temperature of -7ºC. Dry conditions were noted over the area. The 500-hPa chart depicted a trough of low pressure to the west of the accident site with winds from the north over western California and from the southeast at 5 knots over the Reno area with a temperature of -9ºC, and a dew point temperature of -45ºC and indicated dry air conditions or the absence of clouds over the area. Wind and Temperature Aloft Forecast The NWS Winds and Temperature Aloft Forecast for Reno current during the accident period indicated light and variable winds at 6,000 ft; wind from 130° at 7 knots with a temperature of 13°C at 9,000 ft; and wind from 190° at 11 knots with a temperature of 6°C at 12,000 ft. Sounding The closest upper air sounding from the NWS Reno Weather Forecast Office at 1700 indicated a lifted condensation level (LCL) and level of free convection (LFC) at 10,121 ft above ground level (agl), with a convective condensation level (CCL) at 13,964 ft agl. The wind abruptly veered to the west at 11,000 ft with a low-level wind maximum near 14,000 ft with wind from 250° at 21 knots. The sounding supported strong thermal activity from the surface through 17,000 ft. Analysis of the sounding profile indicated a high probability of moderate turbulence at 12,000 ft or immediately below the low-level wind maximum with an 8.1 knot/1,000 ft vertical shear. Solar Data At the time of the accident, the altitude and azimuth of the sun when viewed from Slide Mountain would have been about 58° and 182°, respectively. Rear Seat Occupant The glider’s co-owner, who occupied the rear seat, held a private pilot certificate with a glider rating. He did not hold a current medical certificate; however, the provisions of 14 CFR 61.23 notes that pilots exercising the privileges of a glider category rating are not required to hold a medical certificate. Pilot logbooks were not available for review. Friends and acquaintances of the pilot stated that he had extensive flight experience in gliders, flew most weekends during the flying season, and had well over 1,000 hours of flight time. He had organized multiple similar tasks and was described as a “purist” who specialized in long-distance flights and held multiple records. One witness stated that the pilot flying aerobatics was, “not in his DNA.” Records on file at the pilot’s local soaring club indicated that his most recent flight review was completed on March 31, 2018. Front Seat Occupant The front seat pilot held a private pilot certificate with ratings for airplane single-engine land and glider. He did not hold a current medical certificate. No pilot logbooks were recovered; however, he had similar levels of flight experience and time as the rear seat pilot and owned a high-performance glider that he flew regularly. Rear Seat Occupant According to the autopsy performed by Washoe County Regional Medical Examiner's Office, the cause of death was blunt force and thermal injuries. Only two coronary arteries were available for examination, revealing that both the left anterior descending and circumflex arteries were 95-99% occluded. Toxicology testing performed by the FAA’s Forensic Science Laboratory identified terazosin in liver and muscle. According to personal medical records from the pilot’s care at a multispecialty group practice, he was being treated for hypertension, high cholesterol, obstructive sleep apnea, prostatism, and over the last 3 months he had received physical therapy for upper back pain. His medications included terazosin as well as amlodipine and losartan to treat his blood pressure. None of these medications are considered impairing by the FAA. Front Seat Occupant Autopsy results indicated that the cause of death was blunt force and thermal injuries. The heart was not examined due to the extent of injury and the brain did not demonstrate gross underlying natural disease. Toxicology testing performed by the FAA’s Forensic Science Laboratory did not identify any tested-for substances. No grossly evident soot was present in the upper airways of either occupant. The Schempp-Hirth Duo Discus T is a high-performance, two-seat, T-tail glider constructed primarily of carbon fiber and glass fiber-reinforced composite materials. Its engine is referred to as a "sustainer" engine and is not sufficient for takeoff use. The engine/propeller combination was mounted on a pylon behind the cockpit, and the entire assembly retracted into the fuselage when not in use. The other owner stated that the accident pilot was apprehensive about using the engine, and both he and other acquaintances stated that he regularly performed off-airport landings rather than use the engine to return to the departure airport. The glider was equipped with flight controls at both pilot stations as well as a supplemental oxygen system, which was filled to 2,000 psi the day before the accident. Maintenance records were not recovered for the glider and presumed to have been destroyed in the fire. An invoice from the facility that performed the last maintenance event indicated that an annual inspection was competed on May 31, 2018. At that time, an avionics upgrade was performed, which included the installation of a new altimeter, air speed indicator, and integrated navigation and variometer system. According to the other owner, the glider had accrued about 300 hours of flight time at the last annual inspection. According to the flight manual, the maneuvering speed (Va) was 97 kts. The manual stated that full deflections of control surfaces may only be applied at this speed and below, and stated, “Do not make full or abrupt control movements above this speed as the aircraft structure might get overstressed.” The glider was not approved for aerobatic maneuvers. The stall speed (Vs) with the powerplant retracted and airbrakes closed at a maximum gross weight of 1,543 lbs, was 32 kts. The never-exceed speed (Vne) was 135 kts. The manual stated, “Do not exceed this speed in any operation and do not use more than 1/3 of control deflection.” The airbrakes may be extended up to Vne; however, the manual stated they should only be used at such high speeds in emergency or if the maximum permitted speeds are being exceeded inadvertently. The stall recovery technique while flying straight ahead or in a bank called for “firmly easing the control stick forward and, if necessary, applying opposite rudder and aileron.” The manual-provided in