Standard Cirrus Vorfall auf der Montagne de Boudry aufgrund von Strömungsabriss bei turbulenten Bedingungen

Am 18. April 1971 ereignete sich ein Vorfall mit einem Schempp-Hirth Standard Cirrus am Südhang der Montagne de Boudry in der Schweiz. Der Pilot, der von Lausanne-La Blécherette gestartet war, traf auf turbulente Bedingungen während des Rückflugs eines Streckenflugs. Beim Ausführen von Achterkurven, um an Höhe zu gewinnen, kam es zu einem Strömungsabriss, und das Segelflugzeug sank in die Bäume, was zu schweren Schäden am Flugzeug und schweren Verletzungen des Piloten führte. Die Untersuchung bestätigte, dass der Strömungsabriss in geringer Höhe auftrat, was eine Rückkehr zum normalen Flug verhinderte.

1. Cross-country return leg: During the return leg of a Lausanne–Courtelary cross-country flight after turning Courtelary, the pilot continued in increasingly weak lift toward Colombier.
2. Weak plateau lift: On the way back from Courtelary the pilot encountered poor thermals over the Plateau and was unable to find usable lift, descending to about 1380–1400 m MSL near Colombier.
3. Low height near ridge: The pilot approached the south slope of Montagne de Boudry at an estimated only 50–80 m above the treetops to use slope lift.
4. Turbulent slope lift: Along the south face of Montagne de Boudry the pilot encountered turbulent updrafts with peaks of +3 to +4 m/s in a combination of thermal and wind effects.
5. Low-speed ridge turn: While flying figure-eight patterns along the slope, the pilot initiated a second turn away from the ridge at a speed that was insufficient for the prevailing turbulence.
6. Right wing stall and loss: During this second turn the right wing suddenly dropped, the glider stalled, and the pilot was unable to obtain any effective response from the controls before losing control.
7. Crash - serious injury: The glider struck the top of a tree and then fell nose-first between the trees to the forest floor on the south slope of Montagne de Boudry, seriously injuring the pilot and heavily damaging the aircraft.