Crash d'un ASW 20 lors d'une tentative d'atterrissage en campagne près de Sumiswald, Suisse

Le 7 juin 1978, un Alexander Schleicher ASW 20 s'est écrasé lors d'un vol de compétition près de Sumiswald, en Suisse. Le pilote, participant aux Championnats suisses de vol à voile, a tenté un atterrissage en campagne après avoir rencontré des conditions de faible ascendance. Le planeur a décroché et s'est écrasé, entraînant des blessures mortelles pour le pilote. L'enquête officielle a attribué l'accident à l'incapacité du pilote à maintenir la vitesse minimale, avec des facteurs contributifs tels qu'une décision tardive d'atterrir et des réglages de trim incorrects.

1. Cross-country task: The pilot launched by aerotow from Grenchen at 14:38 for a competition cross-country task and flew normally until reaching the Sumiswald area.
2. Weak lift conditions: In the Sumiswald area the glider encountered generally weak thermals with sink around 0.75 m/s, forcing continuous descent and leading to low altitude.
3. Late landing decision: Despite being low and repeatedly circling in weak lift near Sumiswald, the pilot delayed committing to an outlanding, reducing options for a proper landing pattern.
4. Low final approach: The pilot initiated an outlanding approach over the Chleinegg/Oberlinde area at an estimated 20–25 m above ground, with landing flap setting 5 selected and the trim set tail-heavy.
5. Improper trim setting: The longitudinal trim was set markedly tail-heavy instead of nose-heavy for landing, making it easier to fly below the minimum safe speed in flap 5.
6. Stall on approach: On short final in flap 5 with tail-heavy trim, the glider’s airspeed dropped below the minimum, the flow at the tailplane likely separated, and the aircraft abruptly rolled and pitched into a steep, turning descent.
7. Crash - fatal: The glider impacted the ground in a steep right-turn attitude near Oberlinde, was destroyed, and the pilot sustained fatal injuries shortly after hospital admission.