Atterrissage dur de l'ASK 21 lors d'un entraînement à l'aérodrome de Gruyère après une rupture de câble simulée

Le 12 juin 1994, un Alexander Schleicher ASK 21 a subi un atterrissage dur à l'aérodrome de Gruyère lors d'un vol d'entraînement. L'instructeur a simulé une rupture de câble de treuil peu après le décollage, ce qui a conduit à une montée abrupte par l'élève-pilote. Le planeur a été repris en main près du sol, mais un atterrissage dur a suivi. L'instructeur a subi des blessures graves, tandis que l'élève-pilote a ressenti de légères douleurs au dos. Le train d'atterrissage et la structure du planeur ont été endommagés. Le rapport officiel a identifié un décrochage près du sol et un déploiement prématuré des aérofreins comme causes.

1. Winch launch climb: During a dual training winch launch from runway 36, the ASK 21 transitioned from the initial acceleration into a steep climb of about 40° shortly after liftoff.
2. Simulated cable break: At approximately 20 m above ground and 1–2 seconds after rotation into the steep climb, the instructor released the winch cable to simulate a cable break.
3. Low altitude exercise: The cable break simulation was conducted at very low height near the start of the steep winch climb, leaving little altitude margin for recovery.
4. Premature airbrake use: Airbrakes were observed extended shortly after the transition to glide, reducing acceleration and adding a nose-down pitching moment during the recovery.
5. Student pushes nose down: The student immediately pushed the control stick forward to lower the nose and attempt to land ahead, causing the glider to pitch increasingly toward the ground.
6. Instructor flare and stall: As the glider approached the ground in a steep descent, the instructor pulled the stick back sharply to arrest the sink, and the glider stalled at low height and sank almost flat onto the surface.
7. Crash - serious injury: The glider impacted the ground very hard near the runway threshold, seriously injuring the instructor, slightly injuring the student, and damaging the landing gear and airframe.