What happened
On April 16, 2019, a Schempp-Hirth Discus 2B, registration LN-GDE, was participating in a glider tow operation at Starmoen Airport (ENSM). During the climb, the glider drifted too high while the tow plane was executing a left turn. To correct its position, the pilot utilized airbrakes and a sideslip maneuver. During this correction, the glider's groundspeed increased significantly, reaching approximately 166 km/h, which is much higher than typical tow speeds.
Shortly after the maneuver, a loud impact occurred, and the cockpit canopy shattered. The pilot sustained two deep lacerations above the right eye and suffered a concussion. Despite the turbulence and blood obstructing vision, the pilot successfully managed the aircraft, disconnected from the tow line, and declared a MAYDAY. The pilot completed a normal landing at Starmo and received immediate medical assistance from ground personnel.
The investigation
The investigation, conducted by the glider section of the Norwegian Air Sports Federation (S/NLF) and reviewed by the NSIA, focused on the mechanical integrity of the canopy and the flight dynamics during the tow. Investigators analyzed GPS and barometric flight logs, which confirmed a sudden increase in noise levels and a spike in groundspeed immediately preceding the failure.
Technical examinations of LN-GDE and the tow aircraft, LN-EIC, were performed. No structural defects or latent weaknesses were found in the plexiglass or the adhesive used in the canopy. Furthermore, investigators ruled out external factors such as debris from the tow plane, contact with the tow line, or a collision with a drone.
Findings
- The glider drifted out of its standard position behind the tow plane, necessitating aggressive corrective maneuvers.
- The canopy locking mechanism was found to be insufficiently secure; following the incident, the handle could be moved with very little effort, and the locking pins were not fully engaged.
- The sudden increase in speed and the use of sideslip maneuvers likely created the aerodynamic forces necessary to dislodge the unsecured canopy.
- The primary cause of the incident was the unsecured canopy locking mechanism, which allowed the canopy to open and subsequently strike the glider's wing leading edge, causing it to shatter.