History of Flight
On 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.
The co-owner reported that he and the accident pilot had purchased the disassembled glider in November 2017. The glider had last been flown about 7 years earlier. It was initially trailered to the co-owner's home, where both examined it in detail. The glider design included removable wings for storage and transport. A few months later, it was trailered to the pilot's home. Maintenance records indicated the pilot completed an annual inspection 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).
The accident flight was the glider's first since purchase. It was towed aloft and released about 1227. About an hour later, the pilot radioed that all was well and planned to continue flying; that was the last communication. About 1830, two CCSC pilots departed CA69 on an aerial search. About an hour later, they located two separate sections of wreckage about 5 miles southwest of CA69. Personnel from the Kings County Sheriff's Office accessed the wreckage about 2330 and determined it was the missing glider and the pilot did not survive.
Aircraft Information
The Romanian-designed and built glider, manufactured in 1974 as serial number 38, was a high-performance, single-seat glider constructed almost entirely of aluminum. It featured 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 jettisonable.
FAA records indicated the glider was shipped from the manufacturer to Great Britain in April 1975 and imported into the United States in late 1976. No records of incidents or accidents involving this glider were discovered. Only three Brasov gliders, including the accident glider, were registered in the US at the time. The company had discontinued manufacture and support, possibly as far back as the 1980s.
The wing attach design involved two clevis/tang assemblies. The right wing had four legs (two in top clevis, two in bottom) and the left wing had two single tangs. A pin and cone nut assembly secured them vertically through six aligned holes. The pin had a hex socket and threaded ends. Rotating the pin moved the cone nuts to engage or disengage the tangs and legs. Additionally, six laterally-oriented pin-and-socket mechanisms provided alignment and load transfer.
Wreckage and Impact Information
Investigators accessed the site on May 24, 2018. The wreckage was in remote, rugged terrain in two primary locations. Distribution was consistent with both wings separating in flight and the empennage remaining attached until ground impact. The fuselage impacted in a steep, nose-first descent with minimal ground scars.
Most wreckage was loosely grouped: right wing (fracture-separated into three sections), fuselage, and empennage. The right wing fracture line was near the 2/3 span point. The upper leg of the top clevis was fracture-separated and not located. The lower leg of the top clevis and the two legs of the bottom clevis were undamaged. The pin and cone nuts were present and appeared undamaged; the nuts only minimally engaged the two tangs and did not engage the other two clevis legs.
The left wing was found about 1/4 mile away, in one piece with slight buckling. Its clevis tangs had minor scoring and caked dirt. The fuselage was severely crushed in the aft direction. The cockpit restraint system was found unbuckled. The pilot was found about 200 ft from the fuselage; his parachute was partially deployed with some lines wrapped around a leg. The parachute and harness were not available for examination as the harness was reportedly cremated with the pilot.
Additional Information
The first and only wing installation by the new owners occurred on April 27, 2018, a few weeks before the accident. Assistants reported no significant difficulties, though a tool was needed to complete wing positioning. Postaccident examination of the glider trailer revealed three specialized tools, including alignment pins and an allen-key wrench.
According to the co-owner, the pilot rotated the cone nut pin only about 6 to 8 turns during installation. The right and left wing-fuselage gaps appeared different, and there was excessive play in the joints. During installation, the pilot called the previous owner and concluded that the cone nuts were properly positioned and no further adjustment was needed. The gap issue was addressed by partially backing out the left wing, increasing the forward lift pin extension, pushing the wing back in, and re-securing the cone nuts.
The day before the accident, the pilot emailed another glider owner: "Once the wings were together there was a lot of movement of the wings to the fuselage. It all tightened up after I cranked out the front lift bar tapered pins. Seemed like the gap was bigger in front than the rear. Normal to you?" The email was not answered, and the wings remained in that condition.
Postaccident examination of the pin rotation revealed that 10 rotations were required to fully engage the tangs, 16 for first contact with the outer clevis legs, and 18 for full seating. From clear of legs to fully seated required 23 7/8 rotations, consistent with a theoretical calculation of 22 rotations based on thread pitch.