Thursday, December 26, 2019

Parts Separation from Glider: ICA IS-29D, N38ES; fatal accident occurred May 19, 2018 near Avenal Airport (CA69), Kings County, California

Jan Eric Zanutto

The National Transportation Safety Board traveled to the scene of this accident.

Additional Participating Entities:

Federal Aviation Administration / Flight Standards District Office; Fresno, California
Central California Soaring Club; Avenal, California

Aviation Accident Factual Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Location: Avenal, CA
Accident Number: WPR18FA143
Date & Time: 05/19/2018, PDT
Registration: N38ES
Aircraft: I.C.A.-BRASOV (ROMANIA) IS 29D
Aircraft Damage: Destroyed
Defining Event: Part(s) separation from AC
Injuries: 1 Fatal
Flight Conducted Under: Part 91: General Aviation - Personal 

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.

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. 

Pilot Information

Certificate: Private
Age: 58, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Single
Other Aircraft Rating(s): Glider
Restraint Used:
Instrument Rating(s): None
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: Yes
Medical Certification: BasicMed Unknown
Last FAA Medical Exam: 06/17/2017
Occupational Pilot: No
Last Flight Review or Equivalent:
Flight Time: 601 hours (Total, all aircraft), 1 hours (Total, this make and model)


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 and Owner/Operator Information

Aircraft Make: I.C.A.-BRASOV (ROMANIA)
Registration: N38ES
Model/Series: IS 29D D
Aircraft Category: Glider
Year of Manufacture: 1974
Amateur Built: No
Airworthiness Certificate: Experimental
Serial Number: 38
Landing Gear Type: Hull; Tailwheel
Seats: 1
Date/Type of Last Inspection:
Certified Max Gross Wt.:
Time Since Last Inspection: 0 Hours
Airframe Total Time:
Engine Manufacturer:
ELT: Not installed
Engine Model/Series:
Registered Owner: On file
Rated Power:
Operator: On file
Operating Certificate(s) Held: None

The 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 Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation:
Distance from Accident Site:
Observation Time:  PDT
Direction from Accident Site:
Lowest Cloud Condition: Clear
Visibility:  10 Miles
Lowest Ceiling: None
Visibility (RVR):
Wind Speed/Gusts:
Turbulence Type Forecast/Actual:
Wind Direction: 360°
Turbulence Severity Forecast/Actual:
Altimeter Setting:
Temperature/Dew Point:
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Avenal, CA (CA69)
Type of Flight Plan Filed:
Destination: Avenal, CA (CA69)
Type of Clearance: Unknown
Departure Time: 1337 PDT
Type of Airspace: Unknown

For 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.


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.

Horizontal Stabilizer and Elevator Assembly.

Fractured Right Wing and Aileron.

Fractured Right Wing and Aileron.

Wreckage and Impact Information

Crew Injuries: 1 Fatal
Aircraft Damage: Destroyed
Passenger Injuries: N/A
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 1 Fatal
Latitude, Longitude: 35.937500, -120.218611 

A team of CCSC, FAA, and NTSB personnel accessed the accident site on May 24, 2018. The wreckage was situated in remote, rugged terrain, and was located in two primary locations. The wreckage distribution pattern was consistent with both wings separating from the glider in flight and the empennage remaining attached until ground impact. Ground scars were minimal, and the evidence was consistent with the fuselage impacting in a steep, nose-first descent.

Most of the wreckage was loosely grouped in one location; this included the right wing, fuselage, and empennage. The right wing was fracture-separated into three sections. The empennage was fracture-separated from the fuselage, and the T-configuration horizontal stabilizer was fracture-separated from the vertical stabilizer. The fuselage and horizontal and vertical stabilizers were near one another, consistent with them striking the ground as a single unit. Most of the canopy, including about half its frame, was found near the right wing.

The right wing was fractured/torn into three primary sections, with the fracture line near the 2/3 span point. The three sections included the inboard wing section, the outboard wing section, and the inboard aileron section. These three components were loosely grouped and were part of the primary wreckage. The flap remained fully attached to the wing and appeared only slightly damaged. The air brakes were intact, securely attached to the wing, and found in the retracted position.

The upper leg of the top clevis was fracture-separated at its root and was not located. The lower leg of the top clevis and the two legs of the bottom clevis were essentially undamaged. The machined cone nut holes in the three remaining legs were intact and essentially undamaged. The two pin-capture/assembly guide plates were only slightly damaged.

The pin, with its two cone nuts, was present and captive in the clevis assembly. The pin and cone nuts appeared undamaged. The nuts were symmetrically positioned (up and down) along the pin. The nuts were positioned so that their respective ends protruded only slightly (about 1/8 inch maximum) beyond the innermost (lower leg of top clevis and upper leg of bottom clevis) two clevis legs, so that they only minimally engaged the two tangs. They did not engage the other two (upper leg of top clevis, lower leg of bottom clevis) clevis legs at all.

The fuselage ground impact created a small crater, and the empennage and some canopy and cockpit fragments were located in and around that crater. The fuselage was severely crushed in the aft direction. The fuselage-wing attach structure and surrounding skin panels were significantly crushed or deformed; the crush damage extended to about the normal location of the wing trailing edge.

The cockpit was severely compromised. The instrument panel was severely disrupted, but some intact instruments and portions of instruments remained. The pilot's cockpit restraint system was found unbuckled.

The pilot was found about 200 ft from the fuselage. First responders reported that his parachute was partially deployed, with some lines wrapped around one of his legs. Neither the parachute nor the harness was observed on scene by the investigators a few days after the accident. Subsequent inquiries indicated that the harness had reportedly been cremated with the pilot and was therefore not available for examination. According to the glider co-owner, the parachute was a National Parachute Industries Model NP6/81101-2G. It was manufactured in 2016, had been re-packed in March 2018, and was not equipped with any automatic deployment mechanism.

The left wing was found in one piece about 1/4 mile from the main wreckage group. The wing was slightly buckled in the wingtip-down direction near the 1/3 span point. The flap and aileron were undamaged and remained fully attached to the wing. The air brakes (one panel each on the upper and lower wing surfaces of each wing) were intact, securely attached to the wing, and found in the retracted position. The aileron, flap, and air brake control links appeared intact. The two clevis tangs displayed minor damage, primarily in the form of slight scoring, with caked dirt from ground impact. The machined holes in the tangs (to accept the cone nuts) were intact and essentially undamaged. 

Medical And Pathological Information

The Kings County (California) Office of the Coroner autopsy report indicated that the cause of death was "multiple blunt force trauma." Hydrocodone (liver and muscle) and dihydrocodeine (liver) were detected.

The FAA Bioaeronautical Research Sciences Laboratory, Oklahoma City, Oklahoma, conducted forensic toxicology examinations on specimens from the pilot and reported that no ethanol was detected; hydrocodone (liver and muscle) and dihydrocodeine (liver) were detected.

Hydrocodone (generic and multiple brand names, including Hysingla and Zohydro ER) is a prescription, short-term use medication used to relieve severe pain. Hydrocodone is in a class of medications called opiate (narcotic) analgesics. This medication has the potential to impair mental and/or physical ability required for the performance of potentially hazardous tasks, such as driving, flying, and operating heavy machinery. This medication is disqualifying for FAA aeromedical certification.

Dihydrocodeine is an active metabolite of hydrocodone.

The pilot's family reported that he had undergone several surgeries for neck/back injuries and that he was typically in significant pain. The glider co-owner reported that the pilot normally was in "a ton of pain." The pilot occasionally took some prescription medication for relief from the pain, and he had access to that medication during the period when he inspected and assembled the glider. However, the family was unable to provide any specific information regarding his use of the medication before or during those activities. According to the pilot's son, a few days before the accident, the pilot had a "minor [medical] procedure done to his back." The family and the co-owner reported that the pilot's chronic back pain restricted his ability to physically examine, manipulate, and work on the glider.

Additional Information

Accident Glider Wing Installation

Access to the threaded pin and cone nuts during wing installation was via an approximate 2-inch diameter cutout in the upper fuselage skin. This provided a top-down view of the clevis assembly and only an end-on view of the threaded pin and the top of the upper cone nut.

The first and only time the new owners installed the wings was on April 27, 2018, a few weeks before the accident. According to the persons who helped the pilot install the wings, they did not encounter any significant difficulties during assembly. The owner of a similar glider stated that he needed to use the manufacturer's "lug/camming wrench" to maneuver his wings fully into position. The persons who helped the pilot install the wings reported that the wing installation initially was easy, but then a tool was needed to complete the wing positioning; they were not specific about what the tool was. Postaccident examination of the tools in the glider trailer revealed the presence of three specialized tools, including two alignment pins and the allen-key wrench.

According to the co-owner, the pilot was only able to rotate the cone nut pin about 6 to 8 turns during the wing installation process. In addition, the right and left wing-fuselage gaps appeared to be different sizes, and there seemed to be excessive "play" (relative motion) in the wing-fuselage joints. During the wing installation, the pilot asked the previous owner via telephone about these issues. Although neither of the two assembly assistants heard or were aware of all the conversation details, the pilot's conclusion from that conversation was that the cone nuts had been properly positioned and that no additional activity regarding the pin and cone nuts was needed. The wing-fuselage gap issue was rectified 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 sent an email to the owner of another glider by the same manufacturer stating, "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?"

That email was not answered, and the wings remained installed in that condition for the accident flight.

Forward Left Lift Pin

Pin Rotations for Wing Attachment/Installation

The spacing between the right wing clevis legs (bottom of upper leg to top of lower leg) was very similar to the thickness of the left wing clevis tangs, which resulted in a clevis tang-into-leg fit that was essentially a contact or close-tolerance fit, with very limited or no vertical play.

During postaccident examination, the pin was rotated by investigators to determine the number of full 360° rotations required to move the cone nuts to a series of disengagement or engagement positions. Until the cone nuts made contact with the clevis hole walls, there was very little rotational resistance to the pin. The pin was then rotated to back off the cone nuts so that the top of the upper cone nut was flush with the top face of the lower leg of the top clevis, and the bottom of the lower cone nut was flush with the bottom face of the upper leg of the bottom clevis, so that the cone nuts were positioned to permit the clevis legs to accept the clevis tangs.

The pin was then rotated to drive the cone nuts to various positions, with the following results:

- 10 rotations were required to move the cone nuts to fully engage the clevis tangs
- 16 rotations (6 additional from the immediately preceding configuration) were required to get first contact of the cone nuts in the upper leg of the top clevis and the lower leg of the bottom clevis
- 18 rotations (2 additional from initial contact, the immediately preceding configuration) were required to fully seat the cone nuts

The pin was rotated to completely back off the cone nuts to the ends of the threaded segment of the pin, which positioned them well clear of their respective clevis legs. The pin was then rotated to drive the cone nuts to their fully seated positions; this required 23 7/8 rotations.

The overall cone nut travel distance from just clear of the clevis legs to level with the upper- and lower-most faces of the clevis legs was about 57/64", or about 22mm. The thread pitch of the pin which drove the cone nuts was about 1mm. Therefore, the theoretical number of full 360° rotations of the pin to drive the cone nuts from just clear of the clevis legs to level with the upper- and lower-most faces of the clevis legs was calculated to be 22 turns, which compares moderately well with the previous empirical results. Both values are significantly greater than the number of pin rotations (6 to 8) made by the pilot during actual wing installation.

Aileron Control Assembly/Disassembly Connection.

Fuselage-Wing Flight Control Connections

Each aileron was controlled by a single push-pull rod in each wing. The rod in each wing was positioned near the aft end of the wing, and the rod connected to the fuselage control system at a bellcrank that was part of the fuselage aileron linkage. The rod affixed to the bellcrank via a pin with an integral positive locking mechanism.

Inboard travel of the rod raises (trailing edge up) the respective aileron. Initial or in-service rigging of the ailerons is accomplished by adjusting the rod end at the inboard end of the push-pull rod, but once set, would not normally be adjusted during wing installation or removal. Once the wings were installed, the user would attach each aileron push-pull tube to its respective fuselage bellcrank arm. The design geometry was such that, in the event of improperly or incompletely installed wings, the aileron links could still be connected, and the only manifestation would be that the ailerons would not be simultaneously faired.

Each flap was controlled by a translating pin in the fuselage that inserted into a socket on the inboard end of each flap. The sockets were located near the leading edges of their respective flaps. The pins inserted into the sockets as the wings were moved inboard during wing installation. The translating pins were bussed together to preclude independent flap travel. The pins translated aft and down to extend the flaps. Overall design pin travel was about 1 inch.

The air brake panels were driven via torque tubes in each wing, which were driven by a common torque tube in the fuselage. Each wing torque tube exited the wing root rib just aft of the main spar. All four air brake panels operated in unison; the panels could not be operated independently or in pairs.

The inboard end of each wing torque tube was fitted with a keying pin that was installed perpendicular to the long axis of the tube and protruded beyond the outer diameter of the torque tube. Each wing's keyed torque tube end was designed to insert into a corresponding slotted sleeve on each outboard end of the fuselage torque tube; these mated as the wings were installed onto the fuselage.

The manufacturer's parts catalog (PC) specified that the keying pin was to be retained by a "rivet," part number "2017.D-3-24." The PC illustration depicted the "rivet" as straight pin with no head. The PC contained many unusual, uncommon, or incorrect component names. This appeared to be a language translation (Romanian to English) issue and hindered the evaluation of the wreckage. The "rivet" depiction in the PC diagram was similar to an aviation hardware item called a "roll pin." Internet searches to better identify the "rivet" by its part number were unsuccessful. Attempts to contact the glider manufacturer to obtain clarification were also unsuccessful.

In place of the "rivet" specified by the manufacturer's PC, each of the two keying pins was found secured by a cotter key, the ends of which protruded beyond the outer diameter of the torque tube. These protruding cotter key ends resulted in a wing torque tube maximum diameter dimension that exceeded the internal diameter of the fuselage sleeves, thereby preventing full insertion of the torque tube into the fuselage sleeve. A roll pin with its ends flush with the outer diameter of the torque tube performs the same fastening function as a cotter key but does not exceed the fuselage sleeve internal diameter.

The keying pin of the left wing was symmetrically installed in the torque tube. The left-wing torque tube end and the left fuselage sleeve both appeared undamaged. Attempts to fully insert the left-wing torque tube end into its fuselage sleeve were unsuccessful; the cotter key that secured the keying pin in the torque tube end prevented full insertion. (Figure 4 and Figure 5). The observed insertion distance was only about 3/8 inch, instead of the normal design value of about 3/4 inch. The source and installation date of the cotter key were not determined. Despite this partial connection, the joint was functional; rotation of the fuselage receptacle resulted in rotation of the wing torque tube and actuation of the air brakes.

Figure 4. Left Wing Air Brake Torque Tube with Symmetric Pin.

Figure 5. Left Wing Partially Mated Torque Tube and Fuselage Receptacle.

The keying pin of the right-wing tube end was displaced (Figure 6) so that one end was approximately flush with the outer diameter of the wing torque tube, but the other end extended about twice its normal distance beyond the outer diameter of the wing torque tube. The cotter key remained in place but was highly deformed. The cotter key damage and keying pin displacement were consistent with the application of significant force. The right air brake wing torque tube end could only be partially inserted into its visually undamaged fuselage receptacle; the normal engagement distance of about 3/4 inch was reduced to less than about 1/4 inch. The timing (pre-assembly, during assembly, or during wing separation) of the right keying pin displacement could not be determined.

Figure 6. Right Wing Air Brake Torque Tube with Displaced Keying Pin.

Each of these incompletely mated air brake torque tube junctions, if present during the wing installation process, could prevent the affected wing from being fully and properly abutted to the fuselage and also prevent alignment of the six clevis holes.

There was no evidence to suggest that the pilot ever measured any flight control deflections to confirm full and correct control travel ranges either before or after assembly. The wing installation assistants reported that after the glider was fully assembled, flight control functionality and direction were confirmed, and no anomalies were noted. They did not witness or conduct any control travel measurements.

Manufacturer's Assembly Guidance

The pilot's copies of the manufacturer's Flight Manual (FM) and PC for the glider were reviewed. The origin(s) of these documents could not be determined; it was unclear whether they were modified copies of the manufacturer's original documents or were generated by other individuals or organizations. Investigation attempts to communicate with the manufacturer were unsuccessful.

The FM contained a section of assembly instructions as one of its appendices. The section on wing assembly was a mix of FM "Editions 2" and "2.A" sections. The page describing the wing installation was a copy of an original that contained both typed and handwritten modifications and corrections. The majority of this guidance text was poorly translated English that was sometimes incomprehensible. Additionally, the guidance was generic and did not cite the number or range of pin rotations necessary to ensure proper cone nut engagement. The renditions of the relevant line illustrations in both the FM and the PC were of insufficient contrast and quality to clearly depict the assembly configuration, or many other details. The FM did not explicitly cite any post-installation checks of the wings.

In a separate section, the FM cited the flight control surface travel limits and their tolerances.

Flight Manual Emergency Escape Guidance

The "Emergency Procedures" section of the FM contained guidance regarding canopy jettison. Like the assembly guidance, the text was poorly translated Romanian to English. The guidance stated that canopy jettison required simultaneous manual actuation of two cockpit handles, one each on either (left and right) side of the canopy frame. The FM stated that the left-side handle was secured with safety wire and that a handle force of about 18 pounds was required to break the wire and actuate the canopy release mechanism. Ground impact damage precluded determination of whether the release mechanism had been activated, but canopy component distribution in the wreckage was consistent with at least partial in-flight separation of the canopy from the glider.

Glider Dynamics During Wing Separation

Neither the wing separation sequence nor the separation altitude were determined. In-flight breakup of an aircraft can result in sudden and significant aircraft dynamics that can disorient, injure, or render pilots unconscious. Helmets and securely-adjusted cockpit restraint harnesses reduce a pilot's susceptibility to injury in such events.

The pilot was not wearing a helmet and it was not known how securely his restraint harness straps were adjusted, or whether they were fastened at all at the time of the breakup. No information regarding the pilot's disorientation or injury from the wing separation was available, and no information regarding the pilot's escape efforts or altitude was available.

These are photographs of the Owners' sailplane tool set which were found in the sailplane trailer at Avenal Gliderport several days after the accident. These photos were taken and provided to the National Transportation Safety Board by a colleague/friend of the pilot, and who also helped install the wings on April 27th, 2018.

Full Toolset

Unidentified Tool

Unidentified Tool

Unidentified Tool

Unidentified Tool

Unidentified Tool


Hex/Allen Key


  1. If an airplane has detachable wings I carry a parachute + eay to remove canopy or door. Not negotiable. 3k is worth my life a lot. Wings separating is probaby a pilot's worst nightmare besides a major fire in the cabin, and both require egress from the craft if possible.

  2. you don't know what you don't know.
    " the theoretical number of full 360° rotations of the pin to drive the cone nuts from just clear of the clevis legs to level with the upper- and lower-most faces of the clevis legs was calculated to be 22 turns, which compares moderately well with the previous empirical results. Both values are significantly greater than the number of pin rotations (6 to 8) made by the pilot during actual wing installation. "
    "The day before the accident the pilot sent an email to the owner of another glider by the same manufacturer stating, "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?"

    That email was not answered, and the wings remained installed in that condition for the accident flight."

  3. Unfortunately, the assemblers lacked understanding of the design. The dual cone nut retaining system is designed to be extended all the way until conical nut contact was made through all 6 layers of those tapered-hole tangs. The four "lift pins" between fuselage and wings should be adjusted inward before wing join to avoid preloading the tang fit up and interfering with cone nut free travel. Leaving the four pins in last flown extended positions would cause the hex key to become hard to turn without the cone nuts engaging fully.

    The correct procedure would be to first adjust those four "lift pins" inward before wing joint mating. Insert wings, allowing the 6 spar joint tangs to embed freely for proper alignment, then turn the hex key until the cones seat (wiggle the wings and look through the 2 inch top access hole for the end of the top cone nut to appear as it comes up through the top tang). Only after verifying full cone nut seating in the spar joint would you adjust the four "lift pins" outward to complete it all to a rigid condition ready for flight.

    The available printed material was inadequate, but visually examining the wing attachment arrangement should have led to an understanding of how it worked. Functional inspection of the screw pin and two cone nuts should have included extending them until cone contact seated simultaneously in the upper and lower tangs of the right wing all by itself, which would have also provided understanding of the number of turns required.

    The spar joint design was actually quite robust if properly used. A video showing extension of the cone nuts and normal position of the guide brackets (hook visible over the tang at the 13 second mark) of similar IS-29 right wing is at:

  4. "The pilot also held an FAA mechanic certificate with airframe, powerplant, and inspection authorization ratings."
    I'm curious as to how someone could have a rating like this and not see that this glider was assembled incorrectly - poor Romanian to English translations in the flight manual or not. Can it really be that easy to overlook the inadequate seating of the cone nuts and the incorrect usage of cotter pins in the air brake torque tubes that prevented insertion to the correct depth ? I guess the answer is that in this case, yes.
    What a shame. Sympathies to the friends, colleagues and loved ones of this fellow. RIP.

  5. If something doesn't seem right it probably isn't. Any good mechanic knows this. He knew it but the eager pilot side wanted it to fly.

    If the English assembly instructions were lacking, we have a good reference now after the investigation. Just unfortunate it cost a life.

    RIP on the final glide west.

  6. @markpilot

    All airplanes have detachable wings. With or without tools.

    A parachute MIGHT help in the right circumstances ... Just saying.

    If I'm just going up high enough to do a landing the parachute is a wasted effort.

  7. ^^^^^

    I should have said just high enough to do a landing ...

  8. I owned one of these. Serial #50, VH-GWC. It is hanging in the Caloundra Air Museum, Queensland Australia. The D2 model uses the same wing attachment system, however much more access is afforded due to the removable turtle deck. The D model can occasionally be troublesome to assemble simply because you can't easily see what's going on. An invaluable lesson was to assemble the wings away from the fuselage so that everyone involved in assembling the aircraft could gain an understanding of how two wing panels became mechanically one when the cone nuts were fully seated into the spar tangs. Visualising the various attachment points, load transfer and flap, airbrake, aileron drives was also much clearer, as was imagining the critical alignment plane to make it all slide together when people are hot and sweaty. Gliders are all about symmetry. The wing to fuselage gap should have been the 1st trigger with (lack of) aileron symmetry at zero deflection 2nd. The flap drive possibly would have gone unnoticed, but I do cringe at it being shoved in against its will. The unidentified tools are factory alignment "podger" bars. They are used, if necessary, to align the spar tang holes sufficiently for the cones to engage. First the tapered end, then the blunt end. They show some use. They are intentionally soft so as to not damage the spar. Very sad. Condolences to families.