Grob G-103A Twin II Acro crash during ridge soaring near Claro, Switzerland
On April 10, 1999, a Grob G-103A Twin II Acro was involved in an accident near Claro, Switzerland. The glider, piloted by a Swiss national, lost control during a ridge soaring flight and crashed into a forested area. The pilot sustained minor injuries, while the passenger was seriously injured. The aircraft was completely destroyed. The official report identified the cause as a loss of control due to inadequate mountain flying tactics.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.