What happened
On October 6, 2012, a student pilot was conducting a VFR training flight at Amlikon airfield (LSPA) using an ASK 23 B, registration HB-1967. The flight was a winch-assisted takeoff. As the glider began its ascent, it failed to maintain altitude and struck the grass runway. This cycle of lifting and descending repeated approximately four times, with the aircraft's pitch increasing significantly during each impact. The aircraft eventually struck the runway at a steep angle, approximately 30 degrees on its nose wheel. The pilot managed to release the winch cable during the oscillations, which prevented further damage. The aircraft sustained heavy damage, including a broken fuselage near the tail and damage to the wing and control surfaces, but the pilot remained uninjured.
The investigation
SUST examined the aircraft, the winch equipment, and the circumstances surrounding the pre-flight preparations. The investigation included interviews with the student pilot, the instructor, and the winch operator. Investigators reviewed the pilot's training history, noting that while the pilot had completed 69 previous starts, this was their first time operating the single-seat ASK 23 B. The investigation also reviewed the checklist used by the pilot and the meteorological conditions, which involved a west wind with some turbulence at ground level.
Findings
- The primary cause of the accident was the pilot losing control of the glider during the winch launch.
- The pilot had failed to complete the pre-flight checklist entirely, specifically omitting the step to verify that the airbrakes were locked.
- The pilot was distracted during the checklist process because the instructor provided information regarding the cable readiness while the pilot was still working through the items.
- The airbrakes deployed spontaneously during the takeoff roll because they had not been properly secured.
- The aircraft's increased agility and sensitivity to pitch inputs, compared to the pilot's previous training aircraft (an ASK 21), contributed to the inability to stabilize the oscillations.
Safety action
SUST issued a safety recommendation to the Federal Office of Civil Aviation (BAZL) to ensure that future glider certifications include a safety mechanism to prevent the accidental deployment of airbrakes without requiring additional complex manipulations by the pilot.