N317BA

HISTORY OF FLIGHTOn June 9, 2018, about 1115 mountain daylight time, a LET L-23 glider, N317BA, was destroyed when it was involved in an accident near Moose, Wyoming. The pilot and passenger sustained fatal injuries. The glider was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 sightseeing flight.

The glider was operated by Teton Aviation Center (TAC), based at Driggs-Reed Memorial Airport (DIJ), Driggs, Idaho. The accident flight was a sightseeing flight to view the Teton Range . The operator reported that a sightseeing flight was typically about 1 hour in duration; the first 30 minutes was conducted under tow before the glider released and spent the remaining 30 minutes gliding back to DIJ. The tour predominately flew over the Caribou-Targhee National Forest, encompassing both Idaho and Wyoming.

The tow pilot reported that he and the glider pilot discussed the planned route and briefed safe altitudes for the flight, and then completed the preflight duties for the glider together.

After departing from DIJ, the tow airplane and glider proceeded south and climbed to 11,000 ft mean sea level (msl) and turned west toward Darby Canyon. The aircraft arrived at the foothills of Darby Canyon at 11,500 ft msl and the tow pilot reported that "there wasn't much lift." They then flew east toward the boundary of Grand Teton National Park, gaining "a little lift" off the various ridgelines. The tow pilot reported that, prior to reaching the park boundary, they flew north, paralleling the Teton Range, and were "slowly climbing." About 3 miles west of the South Teton peak, at an altitude of 13,800 ft msl, the glider pilot released from tow at 1037. The tow pilot visually confirmed the release in his rearview mirror and returned to DIJ, where he landed about 1045.

The tow pilot reported that he maintained radio communication with the glider pilot throughout the tow and that they worked together to find lift to gain sufficient altitude for release. The tow pilot did not report any anomalies with the glider during the tow.

The passenger's cell phone was recovered from the accident site and a video recording of the accident flight was retrieved. The recording, taken from the front seat by the passenger, began when the glider was near the Teton Range during the flight, flying over Grand Teton National Park. After about 2 minutes, the footage showed Middle Teton in front of the glider and off to the left; the glider was nearly level with the top of Middle Teton. The pilot stated "this is not good.". The glider then banked slightly right parallel to the ridgeline of Middle Teton.

The last frame where the airspeed indicator was visible showed an indicated airspeed of about 42 kts. The top of the ridgeline was above the altitude of the glider. The glider then appeared to enter a steep descent. The pilot again stated "this is not good." The glider appeared to exit the steep descent as it passed by a cliff marking the end of the ridgeline. The glider then appeared to enter another steep descent. The pilot stated, "I'm in trouble." The glider returned to a neutral pitch attitude but appeared to be descending. The glider was traveling along the ridgeline between Middle Teton and South Teton. As the glider descended, it began a right turn pointing toward the ridgeline. In the last frame before the recording ended, the yaw string mounted in front of the passenger's windshield was hanging about 45° to the right.

When the flight did not return as expected, TAC personnel attempted to reach the glider pilot via radio. At 1220, the glider was reported overdue to the Federal Aviation Administration (FAA), and an alert notice was subsequently issued.

A National Park Service (NPS) search and rescue team consisting of NPS rangers from Jenny Lake Rescue, working in conjunction with Teton County (Wyoming) Search and Rescue, used cell phone data to determine the last known coordinates of the glider. The owner of TAC departed from DIJ about 1435 in a private helicopter and flew to the area of the last known coordinates, where he located the wreckage in steep mountainous terrain about 11,000 ft msl, between Middle Teton peak (12,809 ft msl) and South Teton peak (12,519 ft msl) near the frozen Icefloe Lake in Grand Teton National Park, as shown in Figure 1.

Figure 1: Accident Site Location PERSONNEL INFORMATIONThe pilot previously held an FAA second class medical certificate, which expired on June 20, 2016. Glider operations under 14 CFR Part 91, including personal flights, flight instruction, and sightseeing tour flights, do not require the pilot to hold an FAA medical certificate.

TAC reported the pilot was hired in March 2001. Since the date of hire, she flew 650 hours of instruction in the glider and flew 559 sightseeing tour flights in the glider. The pilot's most recent recurrency flight was conducted on April 27, 2018.

In postaccident interviews, TAC personnel described the pilot as, "very safety conscious," "very by the book," "very cautious," and "always thorough." The pilot's husband reported that she never expressed any concerns about working at TAC and she "enjoyed taking passengers on flights and working with her coworkers." AIRCRAFT INFORMATIONThe LET L-23 Super Blaník Sailplane Flight Manual stated:

The LET L-23 Super Blaník sailplane is a cantilever, high-wing, two-seat glider of all-metal structure with fabric covered control surfaces. Both flight compartments are covered by a single-section canopy which may be emergency jettisoned in flight. Both cockpits are equipped with all sailplane flight control including flight and navigation instrument panels.

The operator kept the glider fully assembled. Review of weight and balance information revealed that, with the pilot and passenger onboard, the glider was within weight and balance limitations for the flight. Review of the glider's maintenance records revealed no evidence of uncorrected mechanical discrepancies. METEOROLOGICAL INFORMATIONThe National Weather Service (NWS) Storm Prediction Center's forecast upper air constant pressure charts for 0600 showed the conditions at about 10,000 ft and 18,000 ft msl.

The charts depicted a long wave trough over the western United States with southwesterly winds over Idaho and Wyoming; wind speeds increased with height with little change in direction. The front side of an upper level trough implies upper-level divergence and general rising motion of the area and the development of clouds and precipitation if adequate moisture is available. Upper level troughs also support surface fronts.

AIRMET Tango was current for moderate turbulence below 16,000 ft over a large portion of the central and southwestern United States. The accident site was located within the boundary of the advisory area.

High-Resolution Rapid Refresh numerical model data was plotted and indicated a lifted condensation level (LCL) about 3,200 ft agl. The profile below 10,000 ft was characterized as conditional unstable with a Lifted Index of -1. The sounding thermal structure did not support any strong thermal activity. The sounding profile indicated that the glider likely encountered southerly winds from 185° at 25 to 27 knots, with the potential for light turbulence at 12,700 ft msl. With this wind direction, no significant orographic lift would be generated on the western slopes of the Teton Mountain Range.

There was no record that the pilot obtained a preflight weather briefing from the FAA contract Automated Flight Service Station (AFSS) provider, Leidos, or from a third-party provider. It could not be determined what weather information the pilot may have reviewed before departure. AIRPORT INFORMATIONThe LET L-23 Super Blaník Sailplane Flight Manual stated:

The LET L-23 Super Blaník sailplane is a cantilever, high-wing, two-seat glider of all-metal structure with fabric covered control surfaces. Both flight compartments are covered by a single-section canopy which may be emergency jettisoned in flight. Both cockpits are equipped with all sailplane flight control including flight and navigation instrument panels.

The operator kept the glider fully assembled. Review of weight and balance information revealed that, with the pilot and passenger onboard, the glider was within weight and balance limitations for the flight. Review of the glider's maintenance records revealed no evidence of uncorrected mechanical discrepancies. WRECKAGE AND IMPACT INFORMATIONPhotos provided by the NPS showed both wings and an impact crater located on a west-facing, snow and ice-covered saddle, which originated at South Teton Peak and extended to the northeast, culminating at Middle Teton peak. The photos showed the fuselage, empennage, and miscellaneous debris located near the base of the saddle by Icefloe Lake.

Figure 2: Accident Site

The wreckage was extracted via external load with an NPS-contracted helicopter to a secure location for a wreckage layout and examination. All major structural components of the glider were accounted for. Flight control continuity was established throughout the airframe, and no preimpact mechanical malfunctions or failures with the glider were noted. ADDITIONAL INFORMATIONPrevious Flight

The day before the accident, the pilot flew with another passenger and provided a sightseeing tour flight. The passenger reported that the flight consisted of four passes on the backside of the Teton mountain range in the Grand Teton National Park, and provided various photos he took during the flight showing the proximity to terrain, as shown in Figure 3.

Figure 3: Aerial View of Terrain, captured the day before the accident flight

During the flight, the pilot talked with the passenger about his lack of interest in roller coasters. The pilot asked the passenger what kind of tour flight he would like to receive. He reported that she jokingly asked if he wanted a "rock and roll flight." The passenger responded that he wanted the re...