Duo Discus left wing fails from spar bonding defect; both crew bail

Both occupants of a Duo Discus bailed out under parachutes after the left wing failed during a thermal flight near Heppenheim; aircraft substantially damaged; no injuries. At ~2,000 m AGL on a straight westbound glide at ~150 km/h GS the pilot pulled the elevator to slow; the left outer wing broke and folded upward, yawing the glider abruptly left. Full right aileron prevented loss of control while the crew bailed — the side-hinged canopy needed considerable force and did not separate. Examination found a 'mirror-smooth' bonding defect between spar web flange and upper CFK cap. A similar Discus CS wing failure occurred in France 4 days later.

1. Aerotow + thermal flight near Heppenheim: The Duo Discus was aerotow-launched with two licensed glider pilots aboard (front-seat pilot ~500 h total) and was thermalling near Heppenheim around 16:30 LT in CAVOK conditions. No water ballast was carried.
2. Brand-new aircraft; first flight on type: The aircraft (Werknr. 387) had been issued its Certificate of Airworthiness on 11 July 2003 — just two weeks before the accident — and had accumulated only 16 launches, 15 landings and 18 flight hours, all aerotows with two on board. The accident flight was the front-seat pilot's first ever flight on the Duo Discus type.
3. Spar web/cap bonding defect: Subsequent examination found a manufacturing bonding defect between the GRP I-web of the wing main spar and the upper CFK spar cap. The detached bond surface was 'mirror-smooth' with no fabric impression, indicating an adhesive failure rather than a structural overload. The wing's load-carrying path through the spar shear web/upper cap joint was thus compromised from manufacture.
4. Left wing breaks at slow-down input: On a straight westbound glide at about 2,000 m AGL and ~150 km/h ground speed, the pilot pulled the elevator to reduce speed. At the elevator input the left outer wing broke at the main spar 10-30 cm outboard of the aileron drive.
5. Wing folds upward; abrupt left yaw: The outer wing piece folded upward and the glider abruptly yawed and rolled left under the asymmetric drag and lift loss.
6. Full right aileron stabilises glider: The front-seat pilot applied full right aileron and managed to stabilise the damaged glider enough to prevent immediate loss of control, giving the crew a window to evacuate.
7. Crew bails; canopy doesn't separate: Both occupants elected to abandon the aircraft. The large side-hinged canopy of the Duo Discus is designed to separate at right-hand frangible hinges in an emergency; on this airframe the front hinge pin had bent and the rear fitting had broken out of the canopy frame, but the canopy as a whole did not separate from the fuselage and required considerable force to open in flight. Both crew nevertheless deployed their emergency parachutes successfully.
8. Both safe; glider in city forest: Both occupants landed uninjured under their parachutes. The Duo Discus came down in the Lampertheim city forest — the right wing caught in tree branches, the fuselage nose-down with the tailboom up, the detached left outer wing and aileron some distance away. Aircraft substantially damaged; minor forest damage.