Accident in Namibia, SH Ventus 2cxm

Just like any other certified glider according to the European CS-22 norm, a 25+ m glider has to undergo successful spin tests, including tests with asymmetrical water ballast. That's how the Eta glider used for certification broke up some years ago: when getting out of a spin with full ballast in one wing, the other empty, the fuselage couldn't resist the torsional load and failed.

Excerpt from the CS-22 rules:

Spinning

CS 22.221 General

(a) Compliance with the following requirements must be shown in all configurations and, for a powered sailplane, with the engine idling. For sailplanes equipped to carry water ballast, the demonstrations of sub-paragraphs (b) to (g) must also be made for the most critical water ballast asymmetry that might occur due to any single malfunction or due to lateral accelerations during a spin.

(b) The sailplane must be able to recover from spins of at least five turns or such lesser number at which the spin changes into a spiral dive, by applying the controls in a manner normal for recovery and without exceeding either the limiting air-speed nor the limiting positive manoeuvring load factor for the sailplane. Tests must be conducted with wing-flaps and airbrakes neutral (see AMC 22.335) and with:
(1) controls held in the position normal for spins;
(2) ailerons and rudder used in opposite directions;
(3) ailerons applied in the direction of rotation.
In addition and where applicable, tests must be conducted in critical combinations of airbrake extension, wing-flap deflection, waterballast including trim water-ballast and with the powerplant extended or retracted. For wing-flap positions for which a VFE limitation is established, the flap position may be adjusted during recovery after the auto-rotation has stopped. (See AMC 22.221 (b))

(c) A sailplane, in the configurations certificated for intentional spinning, must be able to recover from any point in a spin as defined in CS 22.221(b) in not more than one additional turn. In those configurations not approved for intentional spinning, sub-paragraph (d) must be applied. (See AMC 22.221 (c), (d), (e) and (f))

(d) A sailplane in the configurations not certificated for intentional spinning, must still be able to recover from a spin as defined in CS 22.221(b) in not more than one and a half additional turns. (See AMC 22.221 (c), (d), (e) and (f))

(e) In addition, any sailplane must be able to recover from a one turn spin in any configuration in not more than one additional turn. (See AMC 22.221 (c), (d), (e) and (f))

(f) The loss of altitude from the point at which recovery is initiated to the point at which horizontal flight is first regained must be determined in all of the above mentioned cases. (See AMC 22.221 (c), (d), (e) and (f))

(g) It must be impossible to obtain uncontrollable spins with any use of the controls.

CS 22.223 Spiral dive characteristics
If there is any tendency for the spin to turn into a spiral dive the stage at which this tendency occurs, must be determined. It must be possible to recover from the condition without exceeding either the limiting air speed or the limiting positive maneuvering factor for the sailplane. Compliance with this requirement must be shown without the use of air brakes.