What happened
On August 13, 2023, at approximately 19:15 local time, a Grob G103 Twin Astir, registration EC-LJU, was performing a winch launch at the El Tiétar aerodrome in Toledo, Spain. The flight was a private recreational operation with two occupants on board.
During the initial takeoff phase, the aircraft accelerated rapidly, reaching an indicated airspeed (IAS) of approximately 110 km/h. However, shortly after lifting off the ground, the pilot observed a rapid decrease in airspeed. The winch operator reported a significant discrepancy in speeds, noting that while the winch was traveling at over 100 km/h, the glider's speed had dropped to 80 km/h. The cable disconnected from the aircraft without the weak link (fusible) breaking.
As the tension was lost, the aircraft entered a descent. The pilot attempted to stabilize the glider by reducing the pitch angle, but the aircraft continued to lose speed and eventually impacted the ground at a nose-low angle, approximately 240 meters from the runway threshold. The impact resulted in two serious injuries and significant damage to the aircraft's cockpit, landing gear, tail, and wings.
The investigation
The CIAIAC investigation focused on the mechanics of the cable disconnection and the takeoff procedures employed. Investigators examined the winch system, the cable, and the weak link, finding no defects in the equipment. The investigation also reviewed the pilot's flight history and the specific takeoff techniques used at the club.
Technical analysis revealed that the aircraft did not reach an altitude of 30 meters before descending back toward the runway. The investigation noted a contradiction between the aircraft's flight manual—which suggests pushing the control stick forward during high-power launches to avoid excessive pitch—and the pilot's training notes, which encouraged pulling back to initiate rotation.
Findings
- The primary cause of the accident was an incorrectly executed winch launch maneuver, characterized by a premature release of cable tension at an altitude of less than 30 meters.
- The specific reason for the sudden disconnection of the cable, despite the intact weak link, could not be definitively determined.
- The pilot's rotation technique involved a high angle of attack, which, when combined with the loss of tension, caused the aircraft to exceed its critical angle of attack and enter a stall.
- Existing club procedures did not sufficiently emphasize a moderate, progressive rotation or the necessity of immediately aborting the launch by lowering the nose upon sensing a loss of tension.
Safety action
- REC 18/25: It is recommended that the Aeroclub del Tiétar modify its winch launch procedures to emphasize a moderate rotation (lasting at least five seconds) and to mandate that pilots abort the takeoff immediately by lowering the nose if a significant loss of cable tension is detected.