Crash d'un SZD-9 Bocian lors d'un lancement au treuil à l'aérodrome de Samedan entraînant deux décès

Le 4 juillet 1971, un SZD-9 Bocian s'est écrasé lors d'un lancement au treuil à l'aérodrome de Samedan en Suisse. Le planeur biplace, piloté par un instructeur de vol et un élève, a connu un lancement raide et instable. Le câble du treuil s'est détaché à une altitude de 70 à 100 mètres, entraînant un décrochage et une vrille subséquente. L'appareil a percuté la piste, entraînant la destruction du planeur et la mort immédiate des deux occupants. L'enquête a confirmé que la cause était une combinaison de vitesse insuffisante, d'angle de lancement trop raide et de commandes inadéquates après la libération du câble.

1. Winch launch climb: The Bocian HB-648 began a winch launch from the grass runway at Samedan with the trainee in front and instructor in the rear, initial ground roll and liftoff appearing normal.
2. Excessively steep climb: At about 10–15 m above ground the glider was pitched into a very steep climb, causing a noticeable reduction in airspeed and oscillations about the longitudinal and vertical axes.
3. Limited winch experience: Both pilots had very little recent winch-launch experience, with the instructor’s last winch launch eight years earlier and the trainee’s only winch launches two years prior on a different type.
4. Cable auto-release: Around 70–100 m above ground, during a brief heading deviation and correction, the winch cable likely auto-released from the CG hook due to increased cable angle while the glider remained in a steep attitude.
5. Insufficient nose-down input: After cable release the crew apparently did not promptly and sufficiently lower the nose, so the glider continued at a high pitch attitude as the winch pull disappeared and airspeed decayed below stall speed.
6. Stall and right spin: With airspeed below minimum and right rudder likely still applied from the heading correction, the glider stalled and entered a right spin from low altitude.
7. Crash - fatal: After about one spin turn the Bocian impacted the hard-surface runway in a steep nose-down right rotation, destroying the glider and killing both occupants on impact.