Ely, NV, USA
N167TM
Schleicher ASW27
The experienced glider pilot reportedly planned to establish new records for either speed, distance, or both on the day of the accident. He departed about 1119 attached to a towplane. According to data obtained from an onboard air data computer, the glider was released about 5 minutes later at an altitude of about 7,800 ft mean sea level (msl). For the next 17 minutes, the glider made a series of climbing turns and then began a descent toward a nearby mountain range with a field elevation of 8,500 msl. The glider impacted terrain immediately after completing a climbing right turn over the mountain. The glider’s left wing impacted the ground first, and the fuselage and empennage came to rest about 100 ft forward of the initial impact point. The right wing and most of the left wing came to rest about 60 ft forward of the fuselage/empennage, resulting in a long debris field. Postaccident examination did not reveal any preimpact mechanical anomalies or malfunctions that could have precluded normal operation. The examination found that the right wing was mostly intact with some fractures while the left wing was extensively damaged from the impact with the ground. The wing’s water quantity at the time of impact could not be determined by the available evidence. The control cables that open and close the wing ballast tank dump valves were separated from their brass fittings. A laboratory analysis of the control cables and brass tubes revealed that most of the cable separations were the result of the accident sequence, except for one, which was cut by recovery personnel. While there is insufficient evidence to determine what the water levels were at the time of impact, there is also no evidence that suggests the wing ballast control system was not functional at the time of impact. Although weather observations suggested the presence of strong thermals in the vicinity at the time of the accident, which would normally be conducive to soaring conditions, the air was also turbulent, with high wind, conditions favorable to dry microburst development, and strong downdrafts all present at the time of the accident. It is likely that these winds disturbed the thermal activity at the time as evidenced by the pilot’s flight track, which indicated that the glider was being pushed toward the northeast while climbing. The southwest wind would have brought rising air on the windward side of the ridge and downdrafts, and descending air (or sink) over the accident site where the glider was maneuvering just prior to impact. The pilot was attempting to maneuver the glider at an altitude of about 400 ft above ground level over mountainous terrain with full water ballast tanks. The high volume of water carried by the glider at the time would have reduced the overall effectiveness of the pilot’s aileron flight control movements while attempting to navigate through the strong downdrafts and dry microbursts. As there were no preimpact mechanical anomalies with the glider, the evidence suggests the accident was the result of the pilot’s loss of glider control while maneuvering near a mountain ridge in downdrafts and microbursts at an altitude that precluded a successful recovery. Toxicology testing of the pilot’s specimens detected evidence of ethanol in only his muscle tissue. When consumed, ethanol distributes quickly and uniformly to body tissues based on water content. As there was no ethanol in two of the three tissue samples, and the ethanol muscle tissue concentration itself was very low, it is likely that the identified ethanol was from sources other than ingestion. Thus, the identified ethanol did not contribute to this accident.
HISTORY OF FLIGHTOn July 11, 2020, at 1500 Pacific daylight time, an Alexander Schleicher ASW 27 18 (or ASG 29) glider, N167TM, was destroyed when it was involved in an accident near Ely, Nevada. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to witnesses, the accident pilot was an experienced glider pilot who was part of a group that annually flew out of Ely due to its thermal soaring weather. A friend reported that the glider pilot had likely planned to establish new records in speed and/or distance when the accident occurred. Data obtained from an onboard air data computer showed that the glider was released about 1124 on a southeast heading. The glider then turned to the north and began a series of right (clockwise) climbing turns. During the climb, the glider’s position gradually shifted northeast about 2.5 nm. At 1141, after having changed course to counterclockwise climbing turns, the glider made a left turn to the east and began a descent toward the Schell Creek Mountain Range and the location of the accident site. As it approached a group of mountains at an approximate field elevation of 8,500 ft msl, the glider made a slight left turn followed by a right turn toward the south. At 1144:25, the glider made its final right turn and climbed from about 9,400 ft msl to about 9,700 ft msl, which was followed by a steady descent and rapidly progressed into a steep descent. The final data point was captured at 1144:52 and showed the glider at an approximate altitude of 9,167 ft msl and about 900 ft north of the accident site. Figure 1: Flight track from recovered data AIRCRAFT INFORMATIONThe ASW 27 18 (also referred to as “ASG 29” in the flight manual) is a single-seat glider that can be configured with 15-meter or 18-meter-long wingspans, depending on which outboard wing panel is installed. The accident glider was being flown in the 15-meter-long wing configuration on the day of the accident. METEOROLOGICAL INFORMATIONAt 1453, ELY weather reporting facility, located about 4.5 nm west of the accident site, reported wind 210° at 14 knots (kts), with gusts to 27 kts, visibility unrestricted at 10 miles or more, sky clear below 12,000 ft agl, temperature 33° C, dew point 1° C, and an altimeter setting of 30.25 inches of mercury. Calculated density altitude was 9,344 ft, with a relative humidity of 12%. At 1508, a peak wind was reported from 220° at 31 knots. A High Resolution Rapid Refresh (HRRR) numerical model was run for the accident coordinates for 1500 PDT. The sounding identified several low-level features, the stability, and low-level wind field over the area. The sounding depicted an elevation of 8,284 ft with a near temperature of 28° C, a dew point of -2° C, a relative humidity of 12%, and a calculated density altitude of 11,069 ft. The sounding depicted a dry low-level environment with the lifted condensation level and level of free convection (LFC) at 12,172 ft agl. The conditions were conducive to strong thermals from the surface to 21,000 ft with the atmosphere characterized as unstable below 5,000 ft agl. The maximum vertical velocity of potential convective updrafts was calculated at 24 kts. A study of the potential of microbursts indicated outflow winds of 41 kts and the T2 Gust or outflow winds of potential thunderstorms was calculated at 72 kts. The HRRR wind profile indicated a surface wind from 240° at 18 kts, with little variation in direction or wind speed through 15,000 ft. HRRR sounding indicated a predominate mountain wave near 15,000 ft with a maximum vertical velocity of 513 fpm. The winds and temperature aloft forecast for Ely at 9,000 ft msl was for winds from 240° at 16 kts with temperature of 24° C, and at 12,000 ft msl at 17 kts with a temperature of 15° C. The Area Forecast Discussion (AFD) synopsis indicated a tightening of surface pressure gradient across the western portion of the area, expected to increase surface winds with gusts from 20 kts and to 30 kts in higher elevation areas. According to wind data retrieved from the onboard air data computer, the wind was from the south for most of the accident flight at a magnitude of between 10 and 20 kts. Few pilots chose to fly on the day of the accident on account of the wind conditions. Witnesses and other pilots who interacted with the pilot or flew that day noted that the wind conditions were strong, and the air was turbulent. A tow pilot noted the presence of strong thermals that were mixing with winds near the mountain where the accident occurred. The tow pilot also recalled that the buoyancy/shear ratio (B/S ratio), which is used to determine the usability of thermals, was low on the day of the accident. A low B/S ratio indicates that thermals are likely to be broken to unusable. The GOES-17 visible satellite imagery surrounding the period depicted scattered to broken alto-cumulus clouds over the area during the period, which casted shadows on the ground below. The clouds were moving to the northeast and dissipating with time. A review of the NWS weather radar network indicated that the Ely, Nevada, area was located in a gap of radar coverage with coverage below 10,000 ft, to determine if precipitation was associated with the observed clouds over the region. AIRPORT INFORMATIONThe ASW 27 18 (also referred to as “ASG 29” in the flight manual) is a single-seat glider that can be configured with 15-meter or 18-meter-long wingspans, depending on which outboard wing panel is installed. The accident glider was being flown in the 15-meter-long wing configuration on the day of the accident. WRECKAGE AND IMPACT INFORMATIONThe accident site was located about 4.5 nm east of ELY at an elevation of 8,750 ft mean sea level. Photographs of the accident site provided by a witness showed a long and fragmented debris field. Multiple fragments from the left wing were collocated with the area noted as the first point of impact. The fuselage and empennage came to rest about 100 ft forward of the initial impact point and the right wing and most of the left wing came to rest about 60 ft forward of the fuselage/empennage. A postaccident examination of the wreckage was completed after the wreckage was recovered to a secure facility. The outboard right wing had separated from the inboard wing about midspan along the top of the spar. The right wing exhibited some fractures but was otherwise intact as compared to the left wing, which retained most of its top skin, broken at 45° angles. The left while the lower skin had separated into multiple pieces and both the outboard wing panel and left-wing spar had fractured at the wing panel installation point. The flight controls, comprised of the aileron, elevator and rudder, were traced from the cockpit to their respective control surfaces. A piece of intermediate control tube to the elevator control was not recovered; however, the recovered control tubes exhibited evidence consistent with overstress. The elevator trim was intact and unremarkable. The right- and left-wing airbrake systems were traced from the wings to the cockpit through separations that were consistent with overstress and both systems functioned normally at each wing. The glider was equipped with a water ballast system comprised of a total of four ballast tanks: a fuselage tank, a tail tank, and a tank at each wing. The water ballast control levers remained attached to the cockpit with their Bowden cables attached. Both the right and left water ballast tank Bowden cables had separated at the cockpit. Both the left- and right-wing Bowden cables had separated from their swaged tubes, which were both still connected to their plates. The tail water ballast control cable was traced from the cockpit lever to the tail water ballast tank through cable separations. Both the tail and fuselage water ballast control systems were fractured in tension and the fuselage tank had broken but was otherwise unremarkable. The right-wing water ballast control system was traced from the cockpit to the right-wing water tank, which functioned normally when tested. Both the left- and right-wing water ballast control cables were continuous from the control lever at the cockpit to separations at the left and right swedged tubes. The left-wing water ballast tank valve was separated from the left wing during the accident sequence. The valve rod separated from the valve lever, which was intact. ADDITIONAL INFORMATIONFlap Setting According to the flap setting chart in the flight manual, for his weight at the time of the accident, in straight flight the flap setting should have been set at position 1 for speeds over 98 kts. Stall Speeds According to the flight manual, the stall speed for the glider at a gross weight of 1,322 lbs and flap position 1 was 52 kts. The stall speeds in circling flight are increased due to higher load factors. The flight manual showed that the stall speed would have increased by 107% in a 30° turn, 119% in a 45° turn, 141% in a 60° turn, and 200% in a 75° turn. The FAA Glider Flying Handbook (FAA-H-8083-13A), published in 2013, discussed the handling characteristics of a glider carrying large amounts of water ballast. According to an excerpt, water ballast increases stall speed and reduces aileron response during free flight making quick banking maneuvers difficult or impossible to perform. The flight manual contained procedures for recovery from a stall, spin or spiral dive, but did not suggest a minimum altitude for recovering from either of these conditions. Microbursts A microburst is defined as a powerful localized downdraft created by a column of sinking air through the base of a cumulus or cumulonimbus cloud that produces precipitation, with a downdraft core of 6,000 to 7,000 feet per minute, and usually impacts an area less than 2.5 miles with a wind differential of 50 knots or more. This meteorological phenomenon can be divided into dry and wet microburst, depending on rain reaching the surface. A wet microburst is one with from a cumulonimbus type cloud with a defined heavy rain column reaching the surface, while a dry microburst is typically produced from a high based cumulus clouds with virga or rain falling but evaporating before reaching the surface. Both types of microbursts can cause severe wind damage to the surface below and surrounding objects in their path. MEDICAL AND PATHOLOGICAL INFORMATIONToxicology testing performed by the FAA Forensic Laboratory identified ethanol at 0.010 grams per hectogram (gm/hg) in the pilot’s muscle tissue, but no ethanol was detected in brain tissue. Additionally, the non-impairing medication terazosin, which is used to treat an enlarged prostate, was also detected in muscle and liver tissue. Ethanol is a social drug commonly consumed by drinking beer, wine, or liquor. It acts as a central nervous system depressant: it impairs judgment, psychomotor functioning, and vigilance. Ethanol is water soluble, and after absorption it quickly and uniformly distributes throughout the body’s tissues and fluids. The distribution pattern parallels water content and blood supply of the tissue. Ethanol can be produced after death by microbial activity. TESTS AND RESEARCHThe wing and tail assembly water ballast Bowden cables, rocker plates, and two pieces of intermediate Bowden cable; one with and one without its sheathing were submitted to the NTSB material’s laboratory for analysis. The metallurgical examination revealed that four of the five cables exhibited fracture features that were consistent with overstress. The sheathed cable exhibited a fracture consistent with having been cut by a tool such as a pair of wire cutters. Each cable was about the same diameter, 0.060 inch. The brass end fittings attached to the rocker plates each had a hollow portion to insert and crimp the bowden cables. Both brass end fittings had approximately 0.47 inch of allowable insertion depth for its bowden cable. The crimps on both brass end fittings appeared to have been made at similar locations and to a similar level of indentation based on visual comparison. An examination of the open ends of the brass end fittings revealed similar levels of constriction of the bore.
The pilot’s loss of glider control while maneuvering near a mountain ridge in downdrafts and dry microbursts at an altitude that precluded recovery.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
