Incident Astir CS près de Lignerolle : pilote désorienté lors de la descente, planeur détruit

Le 30 septembre 1978, un Grob Astir CS a été impliqué dans un incident près de Lignerolle, en Suisse. Le pilote, qui effectuait un vol d'onde, s'est désorienté lors de la descente en raison d'un givrage sévère sur la verrière et d'une mauvaise visibilité. Malgré les conditions difficiles, le pilote est resté indemne, bien que le planeur ait été détruit lors de l'impact avec le terrain. Le rapport officiel cite comme causes probables le vol dans des conditions météorologiques marginales, la mauvaise visibilité extérieure et la perte d'orientation.

1. Wave flight cruise: After aerotow departure from Montricher, the pilot conducted a wave flight over the Jura and climbed to about 5400 m before starting descent.
2. Severe cockpit icing: At high altitude in approximately -22°C, heavy internal icing formed on the canopy and on the compass mirror, degrading outside view and instrument readability.
3. Descent into poor visibility: During a rapid descent via a gap in the cloud layer near Ballaigues to around 1500 m, the pilot entered an area of snow and generally poor visibility below the stratocumulus.
4. Compass unreadable: Because the compass mirror was iced or fogged and the compass card was hard to see from the semi-reclined seat, the pilot could not reliably read heading.
5. Incorrect heading chosen: Intending to fly heading 090° toward Orbe and possible landing at Yverdon, the pilot inadvertently flew approximately 270°, tracking toward the Jura crest instead.
6. Low flight near slope: Flying level at about 1500 m in snowfall with poor visibility and an only partially de-iced canopy, the glider proceeded parallel to the snow-covered Jura slope with trees visible roughly 100 m below and to the right.
7. Crash - no injury: Still in level flight at about 110 km/h into a 10–15 kt headwind, the glider unexpectedly struck the ground near Bel Coster, rebounded and slid over rocky pasture, destroying the aircraft but leaving the pilot uninjured.