Twin II Acro stalls in sink during low ridge turn

The passenger of a Grob Twin II Acro was seriously injured, the pilot lightly, when the glider stalled in sink on a low ridge turn near Claro; aircraft destroyed. After nearly four hours of cross-country flying, the pilot stopped at the Parusciana ridge to climb a weak thermal. Following the crest toward Pizzo di Molinera in a wide left turn at ~100 m AGL, 50–100 m from the slope, IAS was about 90 km/h. The glider passed from weak lift into strong sink; angle of attack and lift dropped, with no margin to recover. A special bulletin warning of wind shear and turbulence along the Alps was not seen; the type was sluggish at low speeds.

1. Ridge soaring flight: After aerotow departure from Magadino and several hours of cross‑country soaring, the pilot was ridge and thermal soaring along the Parusciana area north of Castione at about 1100 m MSL.
2. Low height near slope: While following the ridge toward Pizzo di Molinera, the glider was flown at an estimated 100 m above ground and 50–100 m laterally from the slope, leaving little margin for recovery.
3. Inadequate speed margin: The pilot flew at about 90 km/h in conditions with forecast wind shear and turbulence, without increasing speed above normal minima despite the low altitude and mountain environment.
4. Encountered strong sink: During a wide left turn following the ridge, the glider transitioned from weak lift into a strong downdraft, abruptly reducing angle of attack and lift at an already low airspeed.
5. Stall and loss of control: At low speed and low height, the glider stalled and the pilot lost control, with insufficient altitude available for recovery.
6. Crash - serious injury: The stalled glider descended into the forested slope near Claro, destroying the aircraft, seriously injuring the front‑seat passenger and slightly injuring the pilot.