What happened
On July 14, 2018, a Duo Discus glider, registration HB-3214, was performing a private flight near the Bellechasse (LSTB) airfield. After a period of soaring over the Jura mountains, the pilot began the approach for landing. To manage the descent, the pilot fully extended the air brakes and initiated a left-hand sideslip.
During this maneuver, the cockpit canopy suddenly opened to the right. The pilot attempted to reach the canopy frame with his right hand to close it, while keeping his left hand on the control stick. This distraction caused the pilot to lose track of the aircraft's altitude. Upon looking back at the flight path, the pilot realized the glider was descending at a high rate and was only a few meters above the ground. In a reflexive attempt to recover, the pilot pulled back on the stick, but the left wing struck a grain field approximately 450 meters before the runway threshold. The aircraft spun 180 degrees and impacted the field backward. The pilot sustained one light injury, while the aircraft suffered heavy damage to the fuselage, wings, and tail.
The investigation
Investigators examined the aircraft's maintenance history and the canopy locking mechanism. While the pilot and ground crew had verified the canopy was closed before takeoff, the investigation focused on why the latch failed during flight. Technical inspections of the HB-3 and 214 revealed no pre-existing defects in the locking mechanism itself. However, the investigation identified that the manufacturer's recommended safety measures for this model had not been implemented.
Findings
- The canopy likely opened due to fuselage deformation caused by aerodynamic loads during the sideslip and airbrake deployment, which reduced friction in the locking mechanism.
- The pilot was significantly distracted by the sudden opening of the canopy and the attempt to close it, leading to a loss of situational awareness regarding altitude.
- The aircraft was not equipped with the safety modifications outlined in the manufacturer's technical note (TM 396-6), which includes installing springs and magnets to prevent accidental opening.
Safety action
- The investigation noted that while the manufacturer's technical note is not mandatory under FOCA regulations, its implementation could prevent similar occurrences.