What happened
On June 9, 2016, a student pilot and an instructor were performing a winch-assisted takeoff at Žamberk Airport (LKZM). Following a standard takeoff roll and transition into a climb, the aircraft reached an altitude of approximately 15 to 20 meters when the tow cable connection was suddenly lost.
Upon the loss of tension, the instructor immediately intervened by pushing the control stick forward to prevent a stall and maintain airspeed. While the instructor managed to level the glider at approximately 3 meters above the ground, the aircraft could not recover sufficient energy, resulting in a heavy landing on the main wheel. The impact caused the glider to veer right and come to a stop off the runway. The student pilot sustained spinal injuries, while the instructor remained uninjured.
The investigation
The ÚZPLN investigation focused on the sudden loss of the tow cable during the climb phase. The investigation established that the student pilot had correctly performed all pre-flight procedures, including a physical check of the cable connection by pulling on the line. The winch operator reported that the takeoff proceeded normally until a sudden, sharp increase in winch RPM occurred, caused by the sudden lightening of the load as the cable disconnected.
Investigators examined the TOST Europa G73 lower attachment point and found no mechanical defects. However, the area contained clumps of dried grass due to recent mulching. The investigation considered that the lower attachment mechanism may have been inadvertently opened when the glider picked up debris from the runway surface during the takeoff roll.
Findings
- The primary cause of the accident was a hard landing resulting from a loss of altitude (sink) following the spontaneous interruption of the winch launch.
- The loss of tow tension was caused by the release of the cable end from the lower attachment point, likely due to debris (dried grass) interfering with the automatic release mechanism during the takeoff roll.
- The instructor's immediate corrective action to prevent a stall was necessary but, due to the extremely low altitude, was insufficient to prevent the subsequent impact with the ground.
- The aircraft, an Alexander Schleicher K7, sustained structural damage to the fuselage, cockpit cover, and wing surfaces.