History of Flight
On July 11, 2020, at 1500 Pacific daylight time, an Alexander Schleicher ASW 27 18 (or ASG 29) glider, registration N167TM, was destroyed in an accident near Ely, Nevada. The pilot was fatally injured. The flight was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
Witnesses reported that the accident pilot was an experienced glider pilot who participated in an annual group that flew out of Ely due to the thermal soaring conditions. A friend stated that the pilot had likely planned to establish new records in speed and/or distance.
Data from an onboard air data computer indicated that the glider was released at about 1124 on a southeast heading. It then turned north and performed a series of right climbing turns, gradually shifting northeast about 2.5 nautical miles. At 1141, after transitioning to counterclockwise climbing turns, the glider made a left turn to the east and began descending toward the Schell Creek Mountain Range. As it approached a group of mountains at approximately 8,500 ft mean sea level (msl), it executed a slight left turn followed by a right turn toward the south. At 1144:25, the glider made its final right turn, climbing from about 9,400 ft msl to about 9,700 ft msl, followed by a steady descent that rapidly progressed into a steep descent. The final data point was recorded at 1144:52, showing the glider at an approximate altitude of 9,167 ft msl, about 900 ft north of the accident site.
Aircraft Information
The ASW 27 18 (also referred to as the ASG 29 in the flight manual) is a single-seat glider configurable with 15-meter or 18-meter wingspans, depending on the installed outboard wing panel. The accident glider was operated in the 15-meter wingspan configuration.
Meteorological Information
At 1453, the Ely weather reporting facility, located about 4.5 nautical miles west of the accident site, reported wind from 210° at 14 knots, gusting to 27 knots; visibility unrestricted at 10 miles or more; sky clear below 12,000 ft above ground level (agl); temperature 33°C; dew point 1°C; altimeter setting 30.25 inches of mercury; calculated density altitude 9,344 ft; and relative humidity 12%. At 1508, a peak wind from 220° at 31 knots was reported.
A High Resolution Rapid Refresh (HRRR) numerical model for the accident coordinates at 1500 PDT depicted an elevation of 8,284 ft with a near-surface temperature of 28°C, dew point -2°C, relative humidity 12%, and density altitude 11,069 ft. The sounding showed a dry low-level environment with the lifted condensation level and level of free convection at 12,172 ft agl. Conditions were conducive to strong thermals from the surface to 21,000 ft, with the atmosphere characterized as unstable below 5,000 ft agl. Maximum vertical velocity of potential convective updrafts was calculated at 24 knots. A study of microburst potential indicated outflow winds of 41 knots and gust or outflow winds of potential thunderstorms at 72 knots.
The HRRR wind profile indicated a surface wind from 240° at 18 knots, with little directional or speed variation through 15,000 ft. A predominant mountain wave near 15,000 ft was indicated, with a maximum vertical velocity of 513 ft per minute.
Forecast winds and temperatures aloft for Ely at 9,000 ft msl were 240° at 16 knots with temperature 24°C; at 12,000 ft msl, 240° at 17 knots with temperature 15°C. The Area Forecast Discussion synopsis noted a tightening surface pressure gradient across the western portion, expected to increase surface winds with gusts from 20 to 30 knots in higher elevations.
Wind data retrieved from the onboard air data computer indicated the wind was from the south at 10 to 20 knots for most of the flight.
Few pilots chose to fly on the day of the accident due to wind conditions. Witnesses and other pilots noted strong, turbulent winds. A tow pilot reported strong thermals mixing with winds near the mountain where the accident occurred, and recalled that the buoyancy/shear ratio was low, indicating thermals were likely broken and unusable.
GOES-17 visible satellite imagery around the period showed scattered to broken altocumulus clouds over the area, casting shadows on the ground, moving northeast and dissipating. NWS weather radar data indicated that the Ely area was in a gap of radar coverage below 10,000 ft.
Wreckage and Impact Information
The accident site was located about 4.5 nautical miles east of Ely at an elevation of 8,750 ft msl. Photographs showed a long, fragmented debris field. Multiple left wing fragments were collocated with 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 and empennage.
A postaccident examination at a secure facility revealed that 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. The left wing retained most of its top skin, broken at 45° angles, while the lower skin had separated into multiple pieces; both the outboard wing panel and left-wing spar had fractured at the wing panel installation point.
Flight controls—aileron, elevator, and rudder—were traced from the cockpit to their respective control surfaces. A piece of intermediate control tube to the elevator was not recovered, but recovered control tubes showed evidence consistent with overstress. The elevator trim was intact and unremarkable. The left and right wing airbrake systems were traced through separations consistent with overstress, and both functioned normally at each wing.
The glider was equipped with a water ballast system comprising four tanks: a fuselage tank, a tail tank, and a tank in each wing. Water ballast control levers remained attached to the cockpit with their Bowden cables attached. The right and left water ballast tank Bowden cables had separated at the cockpit. The left and right wing Bowden cables had separated from their swaged tubes, which remained connected to their plates. The tail water ballast control cable was traced from the cockpit lever to the tail tank through cable separations. 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 and functioned normally when tested. The left and right wing water ballast control cables were continuous from the control lever to separations at the left and right swaged tubes. The left-wing water ballast tank valve separated from the left wing during the accident sequence; the valve rod separated from the valve lever, which remained intact.
Medical and Pathological Information
Toxicology testing by the FAA Forensic Laboratory identified ethanol at 0.010 grams per hectogram in the pilot’s muscle tissue, but no ethanol was detected in brain tissue. Additionally, the non-impairing medication terazosin, used to treat an enlarged prostate, was detected in muscle and liver tissue.
Tests and Research
The wing and tail assembly water ballast Bowden cables, rocker plates, and two pieces of intermediate Bowden cable (one with and one without sheathing) were submitted to the NTSB materials laboratory. Metallurgical examination revealed that four of the five cables exhibited fracture features consistent with overstress. The sheathed cable exhibited a fracture consistent with having been cut by a tool such as wire cutters. Each cable was about 0.060 inch in diameter. The brass end fittings attached to the rocker plates each had a hollow portion for inserting and crimping the Bowden cables, with approximately 0.47 inch of allowable insertion depth. The crimps on both brass fittings appeared to have been made at similar locations and to a similar level of indentation based on visual comparison. Examination of the open ends of the brass fittings revealed similar levels of bore constriction.