Incident DFS Weihe près de Lüterswil en raison d'une défaillance mécanique lors d'un vol de compétition nationale

Le 11 avril 1964, un DFS Weihe a subi une défaillance mécanique lors d'un vol de compétition nationale de vol à voile en Suisse. Le pilote a perdu la pression de contrôle sur la pédale de gouverne droite après sept heures de vol. Malgré la perte de contrôle partielle, le pilote a effectué un atterrissage d'urgence près de Lüterswil, restant indemne. Le planeur a subi des dommages importants. L'enquête a révélé que la défaillance était due à une installation défectueuse du câble de gouverne.

1. Preflight assembly: On the morning of 11 April 1964, club members assembled the DFS Weihe HB-484 from its demounted state in the Bleienbach hangar, including fitting the stabilizer and reconnecting controls.
2. Stabilizer misrigged: During stabilizer installation, the trim tab fork was incorrectly routed between the fuselage wall and the right rudder cable instead of between the two rudder cables, creating an abnormal cable path that was hard to see through the small inspection opening.
3. Preflight check limits: The pilot’s preflight control check, including looking through the handhole, confirmed apparent correct control movement but did not reveal the hidden misrouting due to poor visibility in that area.
4. Rudder cable failure: After about seven hours of flight in evening thermals south of Grenchen, the pilot suddenly lost pressure on the right rudder pedal when the right rudder cable, already abraded by misrouting over a sharp edge, finally broke.
5. Loss of yaw control: With the right cable broken, the rudder was pulled left by the remaining pedal spring, causing control difficulties and a brief spiral dive before the pilot regained partial control.
6. Emergency outlanding: Recognizing the limited controllability and ongoing loss of height, the pilot elected to perform an immediate off-field landing and approached a field near Lüterswil/Biezwil with right sideslip.
7. Outlanding - damage: During the outlanding the glider veered left after touchdown, crossed a road, tipped over a slope, and stopped against trees at the forest edge, leaving the pilot uninjured but the aircraft heavily damaged.