What aircraft was involved and where did it happen?

The accident on 2019-07-19 involved a L-13 Blaník, registration OK-4716, at LKMB, CZ.

What was the probable cause of the accident?

The accident was caused by the inability to successfully execute the landing maneuver following an intentional winch launch interruption at a low altitude, likely exacerbated by insufficient airspeed or variable wind gusts.

Glider hard landing during winch launch abort training

A student pilot and instructor were involved in a hard landing of an L-13 Blaník at Mladá Boleslav after a winch launch was intentionally interrupted at low altitude.

What happened

On July 19, 2019, an L-13 Blaník, registration OK-4716, was participating in a training flight at Mladá Boleslav Airport (LKMB). The flight was part of a student pilot's training program, specifically focusing on flight task number 7, which involves practicing emergency procedures during a winch launch. The objective was to learn how to safely execute a landing on the remaining runway portion after the winch cable tension is released.

The flight crew, consisting of a student pilot and a flight instructor, had coordinated with the winch operator to perform two specific maneuvers where the winch power would be cut to practice a "landing in front" technique. During the first attempt, the winch power was cut at approximately 30 meters. Following this successful demonstration by the instructor, the crew attempted a second takeoff.

During this second attempt, the winch operator reduced power when the glider reached an altitude of approximately 15 meters. Upon the release of the winch tension, the student pilot reacted by pushing the control stick forward to maintain airspeed and disconnected the landing cable. However, the aircraft failed to maintain sufficient lift, resulting in a stall and a very hard impact with the runway surface. There were no injuries to the crew.

The investigation

The ÚZPL_PL_N investigation examined the flight logs, statements from the student pilot, the instructor, and the winch operator, as well as the maintenance records of the aircraft. The investigation also reviewed meteorological data from the Czech Hydrometeorological Institute, which indicated unstable atmospheric conditions with convective clouds and variable surface winds at the time of the accident.

Findings

The winch launch was intentionally interrupted at a low altitude of approximately 15 meters.
The student pilot reacted correctly by attempting to maintain airspeed and following established procedures.
The aircraft suffered significant structural damage, including a deformed fuselage, damaged floorboards, a broken landing gear attachment, and deformed wing components.
The investigation found no evidence of mechanical failure or technical issues with the L-13 Blaník.
The failure to control the aircraft during the landing maneuver following the winch power reduction was the primary cause of the accident.