What happened
On September 29, 2018, a solo flight involving a Standard Cirrus glider, registration OK-1991, ended in a fatal accident in a field near Lenešice, Czech Republic. The pilot was conducting a solo flight to search for and utilize thermal currents under clear skies. After approximately two and a half hours of flight, the aircraft entered a spin. The pilot was unable to recover the aircraft, which continued in a spin until impact with the ground. The pilot sustained fatal injuries.
The investigation
The ÚZPLN investigation utilized flight data from the Open Glider Network (OGN), witness testimonies, and technical examinations of the aircraft's components. Investigators focused on the flight's critical phase, during which the aircraft transitioned from steady flight into a series of climbs, descents, and turns.
Technical experts performed a specialized examination of the ovality of the wing assembly (VOP) console eye and its bronze bushings. This examination revealed that a brass bushing, which should have been seated in the console eye, was missing. Furthermore, investigators examined the aircraft's center of gravity, noting that the pilot's weight, even with added ballast, resulted in a relatively low total mass, which influenced the aircraft's longitudinal stability.
Findings
- The primary cause of the accident was the loss of control due to a missing brass bushing in the wing assembly console eye.
- The absence of this bushing created excessive play (looseness) between the steel pins and the console eye.
- Under aerodynamic loads, this play allowed the steel pins to shift axially out of their bronze bushings, altering the angle of attack of the wing assembly.
- This mechanical shift restricted the longitudinal control of the glider, making it impossible for the pilot to recover from the spin.
- A contributing factor was the aircraft's high center of gravity characteristics, exacerbated by the pilot's low weight.
- The brass bushing had not been properly pressed into the console eye, allowing it to fall out during assembly or flight.