ASG 32 low ridge collision in weak conditions

An ASG 32 with two on board struck a rock face at Pra Roua in Valais, Switzerland; both were fatally injured and the glider destroyed. After an aerotow from Sion the pilot worked weak conditions along the Prabé-Crêta-Besse ridge while other club gliders returned. He continued low ridge passes with no altitude gain, flying perpendicular to the relief at insufficient height. After an east-to-west crest crossing at about 30 m the glider entered a left turn at roughly 40 degrees bank with 1.5 m/s sink. About 20 seconds later it hit the west face, with persistence in weak ridge soaring at very low terrain clearance the central factor.

1. Aerotow — ridge soaring: After an aerotow departure from Sion, the ASG 32 spent an extended period ridge and weak thermal soaring along the Mayens-de-la-Zour area before moving north along the Prabé–Crêta-Besse ridge near Pra Roua.
2. Weak soaring conditions: Throughout the flight the pilot encountered weak thermals and marginal ridge lift, requiring him to 's’accrocher' and preventing significant altitude gain while other gliders left the area to return to Sion.
3. Low height above ridge: In the Pra Roua area the glider conducted repeated ridge passes and turns at relatively low height above the crest, including a crossing of the ridge at only about 30 m clearance with limited altitude margin.
4. Tight turn near crest: At about 15:40:40 the pilot crossed the ridge east-to-west at roughly 30 m height and then entered a left turn with about 40° bank and a descent rate of 1.5 m/s, setting up another low crossing back toward the crest.
5. Continued low ridge turns: Instead of breaking off to gain safer clearance, the pilot maintained the left turn and continued ridge-hugging flight with ground speed around 120 km/h while losing altitude relative to the earlier crossing point.
6. Insufficient terrain clearance: A few seconds after the last recorded FLARM position, the glider, still in a left turn toward the ridge crest and about 20 m below it, was on a collision course with the steep rocky slope.
7. Crash - fatal: The ASG 32 impacted the steep rocky face of Pra Roua almost perpendicularly and slid down the slope, destroying the glider and fatally injuring both occupants.