What happened
On July 4, 2017, at approximately 07:15, a student pilot and instructor were preparing for their first flight of the day at the Bielsko-Aleksandrowice (EPBA) aerodrome. During the pre-flight inspection, the instructor noticed the control stick moving spontaneously toward a neutral position.
Upon further testing, the instructor determined that while the ailerons were functioning correctly, the elevator was non-responsive to control stick inputs, despite the stick moving without resistance. To investigate, the instructor moved the elevator manually from the tail section of the SZD-9 bis Bocian 1E, but this movement failed to translate to the cockpit controls. After inspecting the control linkages through inspection ports, the instructor discovered that the elevator pushrod was hanging loose due to a fractured threaded adjustment end.
The investigation
The investigation, conducted by the operator, examined the mechanical integrity of the control system. Investigators inspected the fracture surface of the threaded adjustment end and determined that the failure was caused by fatigue. The investigation also looked into the operational history of the aircraft and the physical condition of the components.
Findings
- The primary cause of the incident was a fatigue crack in the threaded adjustment end of the elevator pushrod.
- The glider had been undergoing intensive use as part of a flight training program.
- A slight bending of the adjustment screw was noted, which may have resulted from improper securing of the elevator during ground transport around the airfield.