N38ES

HISTORY OF FLIGHTOn May 19, 2018, at an unknown time, an ICA-Brasov IS-29D Lark glider, N38ES, was destroyed during a flight near Avenal, California following an inflight separation of its wings, and subsequent impact with mountainous terrain. The private pilot was fatally injured. The glider was owned by the pilot and another individual; the pilot was operating the glider as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Avenal Airport (CA69), Avenal, California.

According to the co-owner, he and the accident pilot had purchased the disassembled glider in November 2017. The co-owner reported that the glider had last been flown about 7 years earlier. The glider was initially trailered to the co-owner's home, where the co-owner and pilot examined the glider in detail. The glider design included removable wings to facilitate storage and transport in an enclosed trailer. The glider remained there unassembled, and a few months later, was trailered to the pilot's home. Maintenance records indicated that the pilot completed an annual inspection on the glider in February 2018. Several weeks before the accident, it was trailered to CA69. On April 27, 2018, the pilot, co-owner, and a third individual assembled the glider at CA69. All were members of the Central California Soaring Club (CCSC), which was based at CA69.

The accident flight was the glider's first flight since purchase. The glider was towed aloft and released from the tow plane about 1227. About an hour later, the pilot radioed to his CCSC colleagues that all was well and that he planned to continue flying; that was the last communication from the pilot. About 1830, two CCSC pilots departed CA69 on an aerial search to locate the pilot and glider. About an hour later, they visually located two separate sections of wreckage in the mountains about 5 miles southwest of CA69. Personnel from the Kings County Sheriff's Office accessed the wreckage about 2330 and determined that it was the missing glider and that the pilot did not survive.

Examination of the accident site by Federal Aviation Administration (FAA) and NTSB personnel revealed that both wings had separated from the fuselage. The evidence also indicated that the pilot, who was wearing a parachute, had exited the glider in-flight. The wreckage was recovered to a secure facility for detailed examination. PERSONNEL INFORMATIONPilot

FAA records indicated that the pilot held a private pilot certificate with glider and airplane single-engine land ratings. The pilot was operating under the provisions of BasicMed; his most recent examination was completed on June 1, 2017. Review of his logbook indicated that he had logged about 450 total hours of flight experience, including about 217 hours in gliders. His most recent flight review was completed in April 2017.

The pilot also held an FAA mechanic certificate with airframe, powerplant, and inspection authorization ratings. According to family members and CCSC colleagues, the pilot was a competent and thorough mechanic and an experienced glider pilot.

Co-Owners' Proximity and Schedules

The pilot and glider co-owner lived about an hour's driving time from one another. The pilot lived about 75 minutes' drive time from CA69, and the co-owner lived about 115 minutes' drive time from CA69. According to the co-owner, these distances and the individuals' respective jobs and personal obligations made it difficult for them to schedule joint activities at the glider. AIRCRAFT INFORMATIONThe Romanian-designed and built glider was manufactured in 1974 as serial number 38. The high-performance, single-seat glider was constructed almost entirely of aluminum. It was equipped with ailerons, trailing edge flaps, upper and lower air brakes, and a T-tail trimmable horizontal stabilizer with an elevator. Flight control links were primarily push-pull and torque tubes. The canopy was designed to be jettisonable.

FAA records indicated that the glider was shipped from the manufacturer to Great Britain in April 1975 and was imported into the United States (US) in late 1976. No records of any incidents or accidents involving this glider were discovered. A review of FAA records revealed that only 3 Brasov gliders (including the accident glider) were registered in the US at the time of the accident. A search of multiple internet sources indicated that the company had discontinued manufacture and support of its gliders, possibly as far back as the 1980s.

Wing Attach Design

The glider's wing assembly consisted of the two wings, each of which was fully assembled, complete with its own flap, aileron, air brakes, and relevant control systems/links. The flight control system/linkages were fully contained within each wing (no user installation required) and mated to their fuselage counterparts at the wing-fuselage juncture.

The inboard end of the main spar of each wing was fitted with upper and lower spar cap extensions to enable the attachment of the wings to one another by means of two clevis/tang assemblies. The clevis assemblies were referred to as the "top" and "bottom," corresponding to the upper and lower spar caps, respectively. The right-wing clevis portions had a total of four legs (two in the top clevis and two in the bottom clevis). The two legs of each top and bottom clevis were referred to as "upper" and "lower," referring to each leg's relative position in its respective clevis assembly. (see Figures 1 and 2)

Figure 1. Right Wing Clevis Legs and Pin/Cone Nut Assy

Figure 2. Left Wing Clevis Tangs

The left wing had a similar arrangement, with two single tangs, each of which was designed to be inserted between the two legs of each clevis of the right wing. The tangs and legs were all oriented horizontally. The two tangs and four legs all had approximate 1-inch diameter tapered holes machined into them, oriented vertically, so that when the wings were properly positioned into/onto the fuselage, the six holes were vertically aligned (stacked) at the glider centerline. A pin and cone nut assembly (described below) then installed vertically through all six holes to attach the two wings to one another and concurrently secure them to the fuselage. (see Figure 3)

Figure 3. Pin and Cone Nut Assy

The pin length was slightly less than the distance between the bottom surface of the lower leg of the top clevis and the top surface of the upper leg of the bottom clevis. The pin was threaded on each end, and long tapered nuts (cone nuts) were installed on each end of the pin. Two formed and machined plates were bolted to the inboard end of the main spar of the right wing. These plates retained the pin assembly (oriented vertically) and served as alignment guides during wing installation.

The pin had a hex socket in its top end to enable rotation with a hex (allen) key. The cone nuts had vertical slots that rode on vertical tabs on the machined plates to prevent them from rotating when the pin was rotated. Thus, rotating the pin resulted in relative rotation between the pin and the cone nuts. The cone nuts travel up or down as a function of which nut and which direction the pin was rotated. Rotating the pin in one direction would move the top cone nut up and the bottom cone nut down to sequentially drive the cone nuts through the leg, tang, and the other leg of each clevis and then seat in the respective holes, securing the wings to one another. Rotating the pin in the other direction would drive the cone nuts toward the lengthwise center of the pin, clearing them of the clevis leg and tang holes and allowing the wings to be separated and removed.

In the horizontal plane, wing assembly from first tang-to-leg contact to final alignment of the cone nut holes required a relative wing travel of about 1 1/3 inches.

The wing structure also had six laterally-oriented pin-and-socket mechanisms. Each wing root rib was equipped with a forward and aft socket that mated with a pin on the fuselage. These constituted part of the load-transfer path between the wings and fuselage and were sometimes referred to by the pilot as "lift pins." In addition, the right-wing main spar was equipped with two pins that mated to corresponding sockets on the left-wing spar. These six pin-and-socket sets enabled proper wing alignment, provided joint rigidity, and enabled the flight and structural loads to be transferred between the wings and fuselage. When the clevis holes were aligned and secured by the pin and cone nut assembly, these pin-and-socket sets would also be properly mated, securing the wings to one another and the fuselage METEOROLOGICAL INFORMATIONFor the period between the launch of the glider and the discovery of the wreckage, the weather conditions in the region of the departure airport and the pilot's typical soaring area remained clear, with generally northerly winds up to about 18 knots, 10 miles visibility, and temperatures between about 24°C and 31°C.

FLIGHT RECORDERS

The pilot used a "FlywithCE" brand GPS position datalogger. These devices are commonly used by glider pilots due to their very small size and weight. They are self-contained, solid-state devices, complete with internal power supply, which capture and record GPS position and time. The pilot's datalogger was recovered at the accident site but had been damaged. NTSB efforts to recover the data and CCSC efforts to repair the device and recover the data were both unsuccessful. AIRPORT INFORMATIONThe Romanian-designed and built glider was manufactured in 1974 as serial number 38. The high-performance, single-seat glider was constructed almost entirely of aluminum. It was equipped with ailerons, trailing edge flaps, upper and lower air brakes, and a T-tail trimmable horizontal stabilizer with an elevator. Flight control links were primarily push-pull and torque tubes. The canopy was designed ...