Crash du Piper PA-18-150 près de Vilan après rupture du câble de remorquage avec le Pilatus B4-PC 11AF

Le 5 août 1977, un Piper PA-18-150 remorquant un Pilatus B4-PC 11AF a décollé de l'aérodrome de Bad Ragaz. Pendant le vol près de Vilan, le câble de remorquage s'est détendu puis s'est cassé, provoquant la perte de contrôle du Piper qui s'est écrasé sur une pente raide. Le pilote du Piper a été tué dans l'accident, et l'avion a été détruit. Le pilote du planeur a réussi à retourner sain et sauf à l'aérodrome. L'incident s'est produit en Suisse, sans dommages à des tiers signalés.

1. Aerotow ridge climb: During an aerotow from Bad Ragaz toward the Vilan area, the tow combination climbed along the ridge after passing the Sadreinegg ridge in rising air.
2. Tight turn near slope: After crossing the Sadreinegg ridge, the towplane initiated a relatively sharp right turn toward the mountainside and then abruptly reversed into a sharp left turn in close proximity to the slope.
3. Low height and clearance: The tow was being flown with low height above ground and small horizontal distance from the slope, below prescribed minima, leaving little margin to recover from upset.
4. Slack tow rope: During the right turn the glider climbed slightly above the towplane, causing the tow rope to slacken and hang through.
5. Glider fails to release: When the towplane disappeared from his field of view in the steep left turn and turbulence, the glider pilot took the release handle in hand but did not immediately jettison the tow.
6. Rope snatch and break: As the towplane reversed into the sharp left turn in turbulence, the slack rope suddenly came taut, abruptly lifting the towplane’s tail toward the slope and then failing at the glider-side splice instead of at the weaker intended weak link.
7. Crash - fatal: At very low height the towplane, upset by the rope snatch and close to the steep terrain, entered a near-vertical descent and impacted the slope fatally injuring the tow pilot, while the glider released and later landed safely back at Bad Ragaz.