What happened
On January 3, 2016, an SZD-9 Bocian D glider, registration SP-3616, was performing a winch launch at the Turbia airfield (EPST) in Poland. After a successful takeoff and initial climb, the aircraft reached an altitude of approximately 450 meters when the pilot heard a loud cracking sound. This was immediately followed by the sudden release of the winch cable. The pilot was able to complete a standard circuit and land the aircraft safely at the airfield. There were no injuries to the pilot.
The investigation
The PKBWL investigation focused on the structural integrity of the keel assembly. Following the incident, the glider fuselage was transported to a specialized glider service facility in Międzybrodzie Żywieckie for a detailed technical assessment by experts in wooden aircraft repair.
Technical inspections revealed that the keel spar had cracked at the location of the front bolts used to secure the lower attachment point. This fracture caused the keel board to be torn away from the airframe along with the attachment hardware. The investigation identified several manufacturing and maintenance issues, including poorly executed glue joints on the left side of the keel board and an improperly executed reinforcement strip on the lower wall. While the wood itself was found to be free of rot, the investigators noted that the structural strength of the wood had likely been weakened by the age of the aircraft.
Findings
- The primary cause of the incident was an improper structural design of the lower attachment point.
- Poorly executed adhesive bonds between the keel board and the fuselage contributed to the failure.
- The age of the aircraft resulted in a general weakening of the wooden airframe components.
Safety action
A safety recommendation was issued to the type certificate holder, Zakład Szybowcowy "Jeżów" Henryk Mynarski, to suspend winch launches for SZD-9 Bocian D gliders until a modification to the attachment point design is implemented.