What happened
On July 25, 2003, a Schempp-Hirth Duo-Discus glider was conducting a thermal flight near Heppenheim, Germany, with two occupants on board. At approximately 16:32 local time, while the pilot was attempting to decelerate by pulling on the elevator, the left outer wing failed. The breakage caused the wing fragment to fold upward, resulting in an abrupt leftward change in the aircraft's flight path. The pilot managed to stabilize the aircraft using full right aileron input, preventing an uncontrolled descent.
Due to the severely restricted controllability of the aircraft, the two occupants decided to perform an emergency bailout. During the exit, the pilot reported significant difficulty because the canopy did not separate from the fuselage as expected. Ultimately, both occupants landed safely using their parachutes.
The investigation
The BFU examined the wreckage, which was located in a forest near Lampertheim. The investigation included an analysis of the aircraft's GPS logger, which recorded flight parameters such as altitude, coordinates, and ground speed. The wreckage showed the right wing caught in trees, while the left wing stub was on the ground. The investigation also involved representatives from the manufacturer, Schempp-Hirth, and the German aviation authority, the LBA.
Investigators focused on the structural integrity of the wing spar and the manufacturing processes used by various suppliers. The investigation also looked into the canopy's release mechanism, noting that the components designed as intended failure points did not function correctly during the emergency egress.
Findings
- The primary cause of the accident was a manufacturing defect involving a failed adhesive bond approximately 20 cm in length between the GFK (glass fiber reinforced plastic) spar web and the CFK (carbon fiber reinforced plastic) upper spar cap.
- This lack of adhesion led to the structural failure of the upper spar cap when the wing was subjected to upward bending loads.
- Quality control processes at the manufacturing sites were insufficient to detect such internal adhesive errors.
- The aircraft was nearly new, having completed only 18 flight hours and 15 landings.
- The canopy release mechanism failed to function as designed, requiring significant force from the crew to jettison the canopy during the bailout.