Duo Discus rudder pedals slip; outlanding into wheat field

A Duo Discus outlanded into a wheat field near Görlitz after a rudder pedal locking failure in flight; substantial damage, both occupants uninjured. About 20 minutes into a thermalling flight, during a circle reversal the front-seat rudder pedals slipped forward to the limit and could not be re-locked, leaving them out of the pilot's reach. The pilot held straight-and-level flight and selected a wheat field ~1 km north of EDBX Görlitz for an outlanding; both wings were damaged on touchdown in the ~1.5 m crop. Bench testing of the locking mechanism afterwards showed secure locking in all positions; no cause was identified.

1. Thermalling, ~20 min after winch start: A Duo Discus took off in a winch launch for a thermalling flight with two occupants; about 20 minutes after launch the glider was circling in lift north of the airfield.
2. Front rudder pedals slip forward: During a change of circling direction, the front-seat rudder pedal lock released and both pedals slid forward to the most-forward position. The pedals could not be reached with the feet.
3. Pedals cannot be re-locked: After pulling the release T-handle, the pilot drew the pedals rearward by hand but could not get them to re-engage the lock; no usable rudder input remained for the rest of the flight.
4. Outlanding selected; field N of airfield: The pilot held straight-and-level flight, notified the flight leader by radio, and chose a wheat field north of the airfield, favouring a long, into-wind track needing no rudder authority.
5. Touchdown in ~1.5 m wheat crop: On touchdown the wings were retarded by the ~1.5 m high wheat, imposing significant in-plane and bending loads on the outer wing structure and fittings before the glider came to rest.
6. Substantial damage; occupants uninjured: Both wings sustained partial skin tearing and deformation of the outer-wing fittings; the glider was substantially damaged, and both occupants were uninjured.