What happened
On August 12, 2023, at 12:16 UTC, a PIK-20D glider, registration OM-5133, was performing an organized aerobatic display near Ronov, Czech Republic. The flight was part of an event involving several aircraft, including various Z-226 models.
During the maneuvers, the pilot was executing a sequence at approximately 300 m AGL. At an altitude of roughly 500 m AGL, the aircraft experienced a sudden structural failure. The glider disintegrated, and the pilot was unable to maintain control, resulting in a vertical impact with the ground. The pilot was the sole occupant of the aircraft and was killed in the crash. There were 0 fatalities among the ground population.
The investigation
The ÚZPLN investigation focused on the wreckage found in a field near Ronov. The debris field was split into two main sections: the right half of the fuselage and cockpit, and a separate section containing the wing spar.
Investigators examined the wreckage of the left wing spar, which had broken away from the fuselage. A specialized fractographic analysis was conducted by the Aviation Research and Testing Institute (VZLU) to determine the failure mechanism. The analysis utilized stereomicroscopy and digital microscopy to examine the fracture surfaces of the composite structure.
Findings
Technical analysis of the broken spar revealed that the failure was caused by a compression failure of the upper flange, which was immediately followed by a tensile failure of the lower flange and the subsequent tearing of the fabric reinforcement between the spar and the ribs.
Microscopic examination identified significant porosity within the composite material, particularly in the epoxy resin. This porosity was found to be uniform across the damaged areas and likely reduced the compressive strength of the composite. While the investigation noted that the aircraft had undergone repairs following a previous landing accident in 2015, the primary cause of the mid-air disintegration was the structural failure of the spar under the high G-loads recorded during the maneuver (which reached up to +6.9 g).