Collision du Ka 8 B avec un arbre lors de l'atterrissage près de Les Pres Vaillons, Suisse

Le 28 mai 1976, un planeur Alexander Schleicher K 8 B est entré en collision avec un arbre lors d'une tentative d'atterrissage près de Les Pres Vaillons, Suisse. Le pilote, visant à compléter un vol de 75 km vers Courtelary, s'est désorienté et est entré dans une vallée étroite. Malgré la présence de zones d'atterrissage appropriées plus tôt dans le vol, le pilote a continué jusqu'à ce qu'une collision se produise. Le planeur a été détruit et le pilote a subi des blessures. Le rapport officiel cite un manque de connaissances géographiques et de navigation comme facteurs contributifs.

1. Cross-country cruise: After an aerotow departure from Fricktal-Schupfart, the pilot cruised along the Jura ridge toward his 75 km goal at Courtelary.
2. Navigation error: Near the Taubenlochschlucht, the pilot misnavigated toward Courtelary by following what he thought was the correct valley, using an inadequately folded 1:200,000 map and then the 1:500,000 ICAO chart.
3. Poor map setup: The topographic map was folded so that the Bielersee and the accident area were not visible, forcing reliance on a small-scale ICAO chart and rough valley counting.
4. Delayed outlanding decision: Despite being in an area with suitable outlanding fields, the pilot continued toward the presumed goal instead of committing to an outlanding by 500 m AGL as recommended.
5. Continued into narrow valley: The pilot flew in low level into the valley between Mont Sujet and the south flank of Chasseral, passing a last suitable pasture near Métairie de Prêles without attempting to land.
6. Trapped low in valley: At low height above the terrain, the pilot attempted to turn but, due to the narrow valley and insufficient altitude, rolled out and continued just above the treetops down the descending valley.
7. Crash - minor injury: About 1.3 km beyond the pass, the right wingtip struck the top of a fir tree, the glider overturned into a near-vertical crash, destroying the aircraft and injuring the pilot.