What happened
On August 31, 2019, a GROB ASTIR 104 IIB glider, registration EC-ESY, was involved in a fatal accident during a winch launch at the La Mancha aerodrome in Toledo, Spain. The flight, conducted under visual flight rules (VFR) for private purposes, lasted only 18.5 seconds from the start of the cable tensioning to the impact.
During the initial phase of the launch, the aircraft experienced a loss of cable tension immediately after rotation. Instead of executing the emergency procedure to release the cable and land on the runway, the pilot requested increased speed from the winch operator. As the aircraft climbed to a maximum altitude of 50 meters, it lost airspeed and entered a stall.
As the aircraft began to descend, the winch operator increased power, causing the cable to regain tension. This sudden tension, combined with the aircraft's high angle of attack and descending state, triggered a rapid right-hand roll. The aircraft's bank angle increased to approximately 120 degrees before impacting the ground 65 meters to the right of the runway centerline. The impact resulted in the death of the pilot and the total destruction of the aircraft.
The investigation
The CIAIAC investigation utilized onboard camera footage from the aircraft to reconstruct the flight sequence. The investigation examined the pilot's flight management, the winch operation, and the aircraft's aerodynamic behavior.
Investigators analyzed the pilot's radio communications, noting that for five seconds during the critical climb and descent phases, the pilot's left arm was occupied with the radio rather than the cable release lever. The investigation also reviewed the winch operator's actions, confirming that the operator applied maximum power in response to the pilot's request, which inadvertently aggravated the roll once tension was restored.
Findings
- The primary cause of the accident was the inadequate execution of the winch takeoff procedure.
- The pilot failed to implement the standard emergency procedure (releasing the cable and landing on the runway) when the loss of traction first occurred.
- The pilot's decision to continue the climb while requesting more power led to a loss of airspeed and a subsequent stall.
- The restoration of cable tension while the aircraft was in a descending, stalled state caused a rapid and unrecoverable right-hand roll.
- The pilot's flight control inputs during the final seconds were ineffective and, at one point, contrary to recovery efforts, as the pilot commanded a right-hand roll just before impact.
- The pilot did not actuate the cable release mechanism at any point during the event; the cable only detached due to the geometry of the impact.