What happened
On April 10, 1999, a Grob G-103A Twin II Acro glider, registration HB-1605, departed Magadino airport via aero-tow for a recreational flight. The aircraft carried a pilot and one passenger. After releasing from the tow plane near Cortasiell, the pilot initially utilized favorable thermal conditions to fly toward the north. However, encountering more challenging conditions, the pilot began a return flight along the Leventina and Riviera valleys.
After nearly four hours of flight, the glider reached the Parusciana area at an altitude of approximately 1,100 meters. Attempting to utilize a weak thermal to regain safety altitude, the pilot initiated a wide left turn along the ridge toward Pizzo di Molinera. During this maneuver, the aircraft was flying at an altitude of roughly 100 meters above the ground and approximately 50 to 100 meters laterally from the slope. The glider suddenly experienced a loss of airspeed and plummeted into the forest below. The impact resulted in one fatality (the passenger, who sustained serious injuries) and one injury (the pilot, who sustained light injuries). The aircraft was destroyed.
The investigation
Investigators examined the wreckage and the flight conditions. The aircraft's weight and center of gravity were within prescribed limits, and the flight manual was present on board, though lost during the crash. While the pilot held a valid glider license and was physically fit with no evidence of alcohol impairment, the passenger was a paraglider pilot with no glider-specific training.
Post-crash analysis of the airframe showed that the forward fuselage shells had separated upon impact, causing the instrument panel to shift toward the passenger. The investigation also noted that while the pilot was experienced, a special meteorological bulletin from Locamo Monti had warned of significant turbulence and wind shear along the Alps—information the pilot was not aware of at the time of the accident.
Findings
- The primary cause of the accident was the loss of control resulting from inadequate mountain flying tactics.
- The glider encountered a strong downdraft while transitioning from an area of lift to an area of sink during a wide turn.
- At low speeds, this reduction in lift likely induced a stall, a risk exacerbated by the known characteristics of the Grob G-103A Twin II Acro being less responsive at low velocities.
- The pilot's awareness of the specific meteorological warnings regarding wind shear was lacking, which would have necessitated maintaining higher minimum speeds.