Arcus terrain collision in slope soaring after lee-side downdraft

A Schempp-Hirth Arcus on a mountain-flying instruction flight struck a mountainside on the Puigmal; the instructor was injured and the glider destroyed. After release at ~2,300 m and slope soaring in the Llo valley in weak lift (~1 m/s) and SW wind, the instructor took the controls to reach the cirque at the valley head. Crossing a rocky spur at low height with planned -2 m/s sink, the glider met a marked lee-side downdraft. The fuselage hit the ground, the left wing detached, and the glider slid ~150 m. BEA cited the lee-side downdraft over the rocky spur, with recent flights in the same sector contributing.

1. Mountain instruction from La Llagonne: Local mountain-flying instruction flight from La Llagonne - La Quillane (66). Aerotow takeoff 12:29 local; release 12:35 at 685 m height (~2,300 m AMSL) at the entrance of the Llo valley. Instructor 70 yo, SPL since 2010, ~6,000 h glider time (110 h in the last 3 months), regular mountain flier and ran perfectioning camps for this club. Pilot 35 yo, SPL since 2019, 500 h glider + PPL(A), wanting to train in mountain flying. Anticyclonic conditions, dry and calm overall; wind forecast 235°/10 kt, vertical movements ±1 m/s, visibility >10 km, 13 °C.
2. Weak lift entering Llo valley: The aerology found in the valley matched the briefing: weak lift around 1 m/s and some sink. The instructor wanted to reach a large cirque at the head of the valley where raptors had been seen climbing well — better lift expected there. The glider was already low after the pilot's initial search.
3. Recent flights in same sector: The instructor had flown the same sector with other students in the preceding days and regularly organised mountain-flying perfectioning camps for the club. BEA contributing factor: possible overconfidence linked to those recent flights.
4. Decision to cross redan at low height: Between the glider and the cirque was a rocky spur (redan). The instructor judged that with current speed and height, and assuming -2 m/s sink, the glider could clear the spur and reach the better lift beyond. He chose to overfly the spur directly rather than turn back toward the valley. The student-pilot was impressed by the proximity of the ground and assumed the instructor would deviate around the obstacle.
5. Marked lee-side downdraft: Just before reaching the redan, the glider entered the descending part of the SW wind on the lee side of the terrain. The LX 8000 recorded 241°/11 kt about a minute before impact (an earlier point showed 221°/17 kt). The actual sink exceeded the assumed -2 m/s and caused a rapid loss of altitude. BEA contributing factor: lee-side sink is difficult to anticipate.
6. No margin to escape toward valley: BEA: with the unexpected sink and low height, the instructor no longer had margin to turn away toward the valley. He lost control of the trajectory relative to the terrain and could not avoid the collision. Last recorded point: 12:38:51 at 44 m above terrain, ~2,440 m altitude.
7. Terrain impact, aircraft destroyed: The fuselage struck the slope; the left wing detached immediately and came to rest ~50 m above the wreckage. The fuselage and right wing slid ~150 m down the steep grass/rock slope and stopped against a tree at ~2,400 m AMSL. No equipment malfunction found post-accident; pilots reported no abnormal glider behaviour. Instructor injured; aircraft destroyed. BEA safety message: terrain safety margins — a recurring theme on the BEA glider accident page.