Nimbus 4DLM loss of control in ridge turn — frontal impact

A Schempp-Hirth Nimbus 4DLM collided frontally with a rock face during ridge flight in the Queyras massif near Vars (Hautes-Alpes); both pilots were fatally injured and the aircraft destroyed. After ~3 hours of mountain soaring — over an hour above 3000 m without supplemental oxygen — the crew began a right turn toward the valley facing crests higher than the glider, likely without a clear natural horizon. Control was probably lost in the turn at low height. BEA cited loss of control in the ridge turn, with possible moderate hypoxia and unclear role-sharing between the two pilots contributing.

1. Alpine cross-country, Queyras: After aerotow from Aspres-sur-Buëch (LFNJ) at 12:57, the Nimbus 4DLM (open class, 26.5 m wingspan, ~820 kg, 46 kg/m² wing loading) was on a ~3 h alpine circuit, spending over 2 h above 2500 m and over 1 h above 3000 m. The two-pilot crew (owner-pilot front, mountain-experienced passenger rear) shared the flying.
2. Heavy open-class in complex air: BEA contributing factor. The Nimbus 4DLM is a large-span, heavy, high-inertia glider — a 26.5 m open-class aircraft takes ~7 s to roll ±45°, vs ~4 s for a 15 m single-seater. Aileron authority is limited; rudder must be used carefully to avoid sideslip-induced spin. The ridge being flown is known by experienced mountain pilots for complex, sometimes violent aerology — turbulence, shear, displaced thermals along the slope.
3. Possible moderate hypoxia: BEA contributing factor. Both occupants spent over 2 h above 2500 m and over 1 h above 3000 m without supplemental oxygen. The French glider manual notes hypoxia effects can appear from 1500 m. EU SAO regulations and AMC guidance recommend supplemental oxygen for the conditions seen on this flight. Possible cognitive and physiological degradation.
4. Two-pilot role-sharing unclear: BEA notes: the investigation could not determine who was at the controls at the time of the loss of control, nor the nature of interactions between the two pilots. FFVP has published guidance on explicit role definition before two-pilot flights ('Mais qui est... commandant de bord').
5. Right turn into higher crests: At 15:55:01, at 3060 m altitude / 250 m AGL, the crew initiated a right turn toward the valley. The view ahead was bounded by crests reaching 3200-3350 m (Pic des Heuvières north, Pic de la Font Sancte / Pic de Panestrel south) — higher than the glider — likely without a clear natural horizon. Speed at turn entry: 119-143 km/h (~1.20-1.45 Vs at flap 0).
6. Loss of control near the rock face: Control of the Nimbus was probably lost during or shortly after the right turn, in the disturbed ridge airflow at low height and low lateral clearance to the rock face. With the heavy open-class glider's high inertia and limited roll/yaw authority, and possibly degraded cognitive state from hypoxia, recovery was not possible in the available altitude/distance.
7. Frontal impact with rock face: The glider hit the rock face frontally with significant energy, then fell downslope. Wreckage found two days later at 2820 m by triangulation from the pilot's phone (FLARM signals were poor in the area; no emergency beacon was installed). Aircraft destroyed; both occupants fatally injured. BEA published safety lessons on open-class glider piloting, ridge-flight margins, mandatory emergency beacon, and two-pilot role-sharing.