DG-1000S airbrakes jam on final from linkage failure, ends in river

The instructor and student of a DG-1000S were lightly injured on a training flight near Kägiswil and the glider was destroyed. On final to RWY 03 the student tried to retract the airbrakes, which were about two-thirds extended; the lever moved freely. A misassembled rod-end fitting in the airbrake linkage had failed under stress. At about 50 m AGL with reduced glide, the instructor took control and rejected a tree-blocked field landing for the runway. The glider struck a house roof and a tree 270 m short of the threshold, overturned and came to rest inverted in the Sarner Aa. A misassembled airbrake rod-end fitting caused the linkage failure.

1. Aerotow training from RWY 03: An instructor and student launched a DG-1000S on aerotow from RWY 03 at Kägiswil for a training flight with a spin/hazard exercise, releasing at about 2,000 m AMSL after an uneventful tow.
2. Rod-end fitting mis-assembled: A rod-end fitting in the airbrake linkage had been incorrectly assembled before the flight and failed under flight loads; such a hidden fault was not detectable by routine checks.
3. Retract fails at ~50 m; lever loose: The student extended the airbrakes to adjust the glide path, then tried to retract them on final at about 50 m; the lever moved freely with no effect as the linkage failed.
4. Instructor takes over; rejects field: The instructor took control and rejected an off-field landing in a field in front of an industrial building because trees blocked the approach, trying instead to reach the runway.
5. Hits roof + tree 270 m short: The last FLARM point at 12:44:13 LT shows the glider at 484 m AMSL and about 90 km/h ground speed. About 270 m before the threshold of RWY 03 it struck the roofs of houses and a tree.
6. Inverted in river; both lightly hurt: The glider overturned and came to rest inverted in the Sarner Aa river; both occupants exited under their own power. The glider was destroyed, with light damage to house roofs.