What happened
On September 4, 2010, at approximately 16:00 SELCH, an L-23 Super Blaník, registration OK-0698, was performing a training flight at Slaný Airport (LKSN). The flight was part of a basic aero-tow training syllabus, conducted by an instructor and a student pilot. The aircraft had been towed to an altitude of approximately 300 m AGL before the glider disconnected from the tow plane over the airfield.
While executing the circuit, specifically in the area between the third and fourth turns, the aircraft entered an uncontrolled descent. Witnesses observed the glider performing a turn with a slight bank before transitioning into a steep, nose-down descent. The aircraft struck the ground at a steep angle of approximately 70–80 degrees. The impact resulted in the death of the student pilot and serious injuries to the instructor. The aircraft was destroyed upon impact.
The investigation
The ÚZPLN investigation examined the aircraft wreckage, witness statements, and the flight records of both the crew and the aircraft. Investigators reviewed the maintenance history of OK-0698, noting that it had undergone its annual inspection earlier that year and was within its weight limits at the time of the accident.
Witnesses provided varying accounts of the final moments; some noted a sudden loss of airspeed during a turn, while others described the aircraft entering a steep spiral. The investigation also examined the meteorological conditions, which were generally favorable, though investigators considered the possibility of localized downdrafts caused by the terrain. A technical examination of the flight controls, including the cables and pulleys, revealed no evidence of mechanical failure prior to the impact.
Findings
- The primary cause of the accident was an uncontrolled descent at low airspeed occurring between the third and fourth turns.
- The exact cause of the loss of control could not be definitively established.
- The instructor was unable to prevent the aircraft from entering the fatal descent.
- There was no evidence of technical malfunction in the aircraft's control systems.
- The instructor was fully qualified and medically fit, while the student was actively undergoing training under the prescribed syllabus.
- Localized wind conditions and potential downdrafts near the terrain may have contributed to the aerodynamic instability.