What happened
On June 23, 2012, a TWIN ASTIR glider, registration OK-3456, was performing an aero tow at Jičín Airport (LKJC) when the pilot noticed the rear cockpit canopy had opened. The incident occurred at an altitude of approximately 50 meters AGL during the climb phase, shortly after a wind gust caused the glider to bounce during takeoff.
The pilot observed unusual noise and discovered the rear canopy was fully swung open to the right. As the airspeed began to drop, the pilot decided to disconnect from the towing aircraft, a WT-9 Dynamic, to avoid endangering the tow plane. Due to the significant aerodynamic drag caused by the open canopy, the pilot was unable to maintain sufficient airspeed and struggled to keep the glider flying, requiring nearly full forward stick input to prevent a stall.
Attempting to avoid obstacles in the terrain, the pilot executed a forced landing to the southeast of runway 30. The glider struck the ground heavily and caught a wing in a field of growing peas. The impact and subsequent 180-degree rotation caused the fuselage to break, the nose to sustain damage, and the front canopy to be torn from its hinges. The pilot was uninjured.
The investigation
The ÚZPLN investigation examined the cockpit locking mechanism and the pilot's pre-flight actions. While the pilot had closed the canopy during pre-flight preparations, the investigation found that the locking bar, which is held in place by a spring, may have rested on the lower eye of the latch without being fully seated.
Testing on an identical aircraft type revealed that even when the canopy appears closed, the rounded front edge of the locking bar can strike the edge of a third eye, preventing the bar from fully entering the locking eye. The spring tension alone is insufficient to complete the engagement; the handle must be pushed forward with force until it reaches its stop to ensure a secure lock.
Findings
- The pilot likely closed the rear canopy during pre-flight but failed to verify that the locking bar was fully engaged in the correct position.
- The unlatched canopy created aerodynamic forces that significantly degraded the glider's controllability and caused the airspeed to decay.
- The necessity of an immediate forced landing at low altitude, combined with the high drag from the open canopy, led to the heavy impact with the terrain.
- The structural failure of the fuselage and the breakage of the canopy were caused by the impact and the subsequent rotation of the aircraft in the field.