Incident Overview
On 9 June 2015, at 20:41 LMT, a training flight involving an instructor-pilot and a student-pilot was conducted on a SZD-9bis Bocian 1E glider at Warszawa-Babice airport (EPBC). The flight, which was part of exercise 6 of the training syllabus, began with a winch launch from the grass runway on heading 10. The takeoff and the left-hand circuit were performed correctly.
Canopy Failure During Approach
During the approach to land after the fourth turn, the front canopy cover began to vibrate and then deflected away from the hinge on the right side. The canopy frame bent and the glazing broke, with pieces of plexiglass flying toward the instructor, who managed to duck. At the same moment, the rear canopy cover detached and was later found slightly damaged on the approach path to runway 10. It was likely that the rear canopy unlatched due to the dynamic air pressure following the destruction of the front canopy.
Landing and Post-Flight Inspection
The instructor safely landed the glider on the airfield with the front canopy frame and remaining pieces of glazing still in place. Post-flight inspection revealed a fracture in the hinge at the front of the frame, along with damage to the glider's canopies, as documented in photographs.
Investigation Findings
The fracture of the front canopy hinge was hidden and could not be detected during visual inspections. According to the glider's owner/user, the hinge had not been repaired or welded since 2009, and senior personnel indicated no recollection of repairs in prior years. However, the investigation commission noted that the hinge failure appeared to occur on a cross-section that had been previously welded, suggesting that the fracture was due to a reduction in strength from an earlier improper repair. Despite this, the owner maintained no repairs were known.
Cause
The probable cause of the incident was operational wear of the hinge of the front canopy frame of the glider.
Safety Actions
No safety recommendations were issued by the investigation commission. However, the aircraft operator discussed the case with mechanics and instructors, emphasizing vigilance for signs of unauthorized repairs and hinge condition. Instructors were advised to include hinge checks in pre-flight inspections.