Incident de Standard Cirrus sur la Montagne de Boudry dû à un décrochage dans des conditions turbulentes
Le 18 avril 1971, un Schempp-Hirth Standard Cirrus a subi un incident sur le versant sud de la Montagne de Boudry, en Suisse. Le pilote, parti de Lausanne-La Blécherette, a rencontré des conditions turbulentes lors du vol retour d'un vol de distance. En effectuant des virages en huit pour gagner de l'altitude, le planeur a décroché et est descendu dans les arbres, entraînant de graves dommages à l'appareil et des blessures graves pour le pilote. L'enquête a confirmé que le décrochage s'est produit à basse altitude, empêchant le retour à un vol normal.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.