What happened
On March 7, 2021, at 12:43 local time, a SCHLEICHDER ASK 13 glider, registration EC-NHC, crashed during a winch-assisted takeoff at the El Tiétar aerodrome in Toledo, Spain. The aircraft was performing a local flight with two occupants on board.
The takeoff was conducted using a winch system located at the opposite end of runway 04. During the initial climb, at an altitude of approximately 100 meters, the towing cable was prematurely released from the aircraft. Following the release, the aircraft did not immediately execute the required emergency procedures. Instead, the glider maintained a high nose-up attitude until it entered a stall. Witnesses observed the aircraft' following the stall with an abrupt nose-down movement, followed by a left-hand turn that transitioned into a near-vertical descent, spinning around its longitudinal axis before impacting the ground. The impact was nearly vertical, and both occupants sustained fatal injuries.
The investigation
The CIAIAC investigation examined the aircraft, the winch equipment, and the flight sequence. Investigators analyzed the state of the towing line and found that the connection between the winch cable and the swiveling link (maillon) was not properly tightened, causing the link to open and the line to break after the initial cable release. However, laboratory tension tests conducted at the Universidad Politécnica de Madrid demonstrated that this loose connection did not cause the premature release itself, as the cable remained attached to the link under the estimated loads.
The investigation also reviewed the pilot's actions and the established emergency procedures. The investigation confirmed that the pilot did not communicate the emergency via radio and failed to follow the established manual instructions, which mandate lowering the nose to regain airspeed and level flight following a cable break.
Findings
- The primary cause of the accident was the loss of control of the aircraft due to the failure to execute emergency procedures following the premature release of the towing cable.
- The pilot did not lower the nose to maintain or regain flying speed after the release.
- The aircraft was in a left-hand bank during the climb, which contributed to the loss of control.
- The threads of the swiveling link were not correctly closed, leading to the subsequent breakage of the towing line after the glider had already disconnected.
Safety action
- It is recommended that the El Tiétar aerodrome implement a procedure to ensure that all elements of the towing line are physically checked for secure closure, rather than relying solely on a visual inspection.