What happened
On June 9, 2015, an instructor and a student pilot were conducting a training flight in an SZD-9bis Bocian 1E glider. The flight, launched via winch from the grass runway at Warsaw-Babice (EPBC) following runway heading 10, proceeded normally through the initial maneuvers. However, during the approach to landing after the fourth turn, the front cockpit canopy began to vibrate and subsequently shifted away from its hinges on the right side. The canopy structure buckled and cracked, causing fragments of the glazing to fly toward the instructor, who managed to duck to avoid injury.
Simultably, the rear cockpit canopy detached from the aircraft. This secondary failure likely occurred due to the sudden-dynamic air pressure changes caused by the destruction of the front canopy. Despite the structural failure, the instructor successfully landed the glider at the airfield. No injuries were reported during the incident.
The investigation
The PKBWL examined the aircraft following the landing and identified a broken hinge on the front canopy frame along with damage to both canopy sections. The investigation focused on the nature of the hinge failure. While the operator initially suggested the failure was due to fatigue, the Commission identified that the fracture occurred at a cross-section that had been previously welded. Although the operator's records and staff did not indicate any recent repairs or welding to the hinge since 2009, the physical evidence suggested that a previous improper repair had weakened the component's structural integrity.
Findings
- The primary cause of the incident was the operational wear and fatigue of the front canopy frame hinge.
- The structural failure was likely exacerbated by a prior unauthorized or improper repair (welding) that reduced the strength of the hinge.
- The failure of the rear canopy was a secondary effect of the aerodynamic disturbance caused by the front canopy's failure.