New Washoe City, NV, USA
N22XC
Schempp-Hirth Duo Discus T
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.
HISTORY OF FLIGHTOn September 2, 2018, about 1336 Pacific daylight time, a Schempp-Hirth Duo Discus T motorized glider, N22XC, was destroyed when it was involved in an accident near New Washoe City, Nevada. The two pilots were fatally injured. The glider was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The flight was part of an informal competition (task), the goal of which was to obtain the shortest flight time between two predetermined locations. Each competitor's flight time would start when their glider flew over runway 2/20 of Truckee-Tahoe Airport (TRK), Truckee, California, and end upon reaching a predefined radius around Marine Corps Mountain War Training Center Heliport (7CL4), Bridgeport, California. There was no specific start time, the gliders departed at staggered intervals throughout the day, and any route could be taken. The pilot of the towplane stated that the accident glider’s takeoff and tow was uneventful, and the glider released after reaching an altitude of 8,000 ft mean sea level (msl), (about 2,000 ft agl) about 3 miles east of TRK over an area known locally as "Hot Rocks." The accident glider and several other gliders flying in the vicinity were equipped with FLARM traffic awareness and collision avoidance systems. This data revealed that, after release, the accident glider began a series of climbing turns over Hot Rocks, reaching an altitude of about 10,500 ft msl. It then proceeded east on a meandering track while performing another series of climbing turns about 3.5 miles west of the summit of Slide Mountain. The last position was recorded at 1333 at an altitude of about 14,500 ft msl, 12 miles east of TRK, and 1 mile west of the 9,698-ft summit of Slide Mountain. Another glider pilot competing in the task reported sharing a thermal with the accident glider for a few minutes beginning about 1331. He stated that they were both over the spine of the mountain just south of the peak of Mt Rose, at an altitude of about 14,000 ft msl. The accident glider appeared to be flying normally and there were no indications of distress. The pilot did not hear any radio calls from the accident glider, and a few minutes later, he flew north to the peak of Mt Rose, where he climbed to almost 16,000 ft. He reported that the lift at Mt Rose was strong, with climb rates averaging up to 10kts. About the time of the accident, a group of paraglider pilots were preparing to launch from an 8,700-ft-high bluff on the eastern face of Slide Mountain. Their attention was drawn to a glider traveling near the face of the slope directly to the east and above their location. One witness stated that, as he looked up, he saw a glider performing a series of “steep back loop” maneuvers, such that he initially thought it was a remote-controlled aircraft. He watched as the glider performed another loop. During that maneuver, he started to hear a high-pitched whistling/vibrating sound, and the wings flexed upwards such that the tips almost touched each other. One of the wings then broke off, followed by a loud "cracking" sound, and the sky was filled with confetti-like pieces of white debris. He could see that the canopy was closed and watched to see if anyone attempted to bail out, but they did not. Another witness stated that when he first saw the glider, it was passing from left to right and performed 2 or 3 full “loops” that lasted about 2 to 3 seconds each. He stated that the wings of the glider were flexing upwards aggressively throughout the maneuvers, and as it rolled out of the final loop, the left wing broke away and struck the tail. A third witness, who was a fixed-wing pilot, stated that he looked up and saw the glider perform a series of loop-like maneuvers, which had a radius of about two wingspans. He described the maneuvers as smooth and progressive, and that the glider appeared to be under positive load throughout. On completion of the second loop, the glider rolled out and the wings appeared to flex up like "rubber" and form a "U" shape when viewed from the front. He heard a buzzing sound, and then the left wing broke away, followed by a very loud snapping sound similar to cracking timber. The glider then immediately entered into a flat spin, and white shards of debris filled the sky surrounding the glider. After the first spin rotation, the glider appeared to level off, and the witness considered the possibility that the pilot had regained control. The glider then rolled over, and the right wing failed. Witnesses stated that they did not see indications that the engine/propeller had been extended, and none of them described seeing any evidence of smoke or vapors trailing from the glider. PERSONNEL INFORMATIONRear 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. AIRCRAFT INFORMATIONThe 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 instructions for spin recovery stated that with a rearward center of gravity, a steady spinning motion is possible that will stop within about ¼ and ½ rotation once the appropriate recovery technique has been applied. With the center of gravity in the foremost position, a steady spinning motion is not possible, and after spin recovery the glider will usually enter a spiral dive, which is accompanied by a rapid increase in speed and acceleration. Recovery could be achieved by easing the control stick forward and applying opposite rudder and aileron. An accompanying warning stated, “When pulling out of the dive, the permissible control surface deflections at Va / Vne are to be observed!” The maneuvering load factor limits (in units of gravity or g’s) were: With airbrakes locked and at Va, +5.3 g, -2.65 g With airbrakes locked and at Vne, +4.0 g, -1.5 g With airbrakes extended +3.5 g (no negative limits specified) Engineers from Schempp-Hirth estimated the speeds and g-loading that would have resulted if the glider had performed a loop with a radius of two wingspans (130 ft) over a 2-second period, as observed by one of the witnesses. Under such conditions, the glider would have needed to travel at a speed of about 240 kts, and would have endured a load of about 40 g. With a loop radius of 165 ft, performed in 4 seconds, the speed would have been about 150 kts, and the glider would have experienced a load of about 12.5 g. The flight manual detailed a series for steps for opening the canopy during emergency situations, and stated as soon as it is opened, it will be torn from its hinges, and carried away by the airstream. METEOROLOGICAL INFORMATIONPilot 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. AIRPORT INFORMATIONThe 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 instructions for spin recovery stated that with a rearward center of gravity, a steady spinning motion is possible that will stop within about ¼ and ½ rotation once the appropriate recovery technique has been applied. With the center of gravity in the foremost position, a steady spinning motion is not possible, and after spin recovery the glider will usually enter a spiral dive, which is accompanied by a rapid increase in speed and acceleration. Recovery could be achieved by easing the control stick forward and applying opposite rudder and aileron. An accompanying warning stated, “When pulling out of the dive, the permissible control surface deflections at Va / Vne are to be observed!” The maneuvering load factor limits (in units of gravity or g’s) were: With ai
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.
Source: NTSB Aviation Accident Database
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