Factual Information
On 24 May 2014, at 06:36 UTC, a L-13 Blaník glider, registration OK-8802, operated by Aeroklub Frýdlant nad Ostravicí, sustained damage during landing at LKFR (Frýdlant nad Ostravicí Airport). The glider was on a circuit flight after a winch launch. The instructor, aged 25, held a valid glider pilot license with instructor rating, and had 334 hours 44 minutes total flight time, including 84 hours 9 minutes as instructor. The student pilot, aged 44, had 5 hours of dual instruction. The glider, manufactured in 1958 with serial number 170102, had accumulated 737 hours 38 minutes total time and 35 hours 37 minutes since the last 500-hour inspection, which was completed on 23 April 2013 with no defects found.
During the approach, the instructor took over control from the student after the fourth turn, extended full airbrakes, and noted insufficient descent. At an altitude of approximately 30–40 meters, he initiated a short slip to increase the sink rate. According to his statement, when attempting to recover from the slip, the controls felt soft and unresponsive; he pushed forward and waited for the glider to gain speed. Shortly before touchdown, he closed the airbrakes abruptly. The glider contacted the ground in a pronounced sideslip, skidding sideways for several meters. Post-accident inspection revealed deformation of the left wing skin, broken left aileron, fractured main spar cap at rib 25, deformation of leading and trailing edges, and minor fuselage damage near the main gear and tailwheel. The glider was not equipped with a flight data recorder.
Meteorological conditions were clear with visibility over 10 km and wind from the south up to 5 m/s, variable near the ground. The accident occurred approximately 110 meters past the threshold of Runway 26, at coordinates N 49° 35' 24", E 018° 22' 57". The crew was uninjured. A breathalyzer test administered by police was negative.
Analysis
The instructor, having taken control for the landing, decided to perform a slip at 30–40 meters above ground to increase the descent rate. The flight manual states that a slip is effective only when used in conjunction with flaps and airbrakes, and should be exited at 25 meters above ground. The instructor reported that the controls felt soft during recovery, suggesting that the glider's speed may have been too low during the slip. Recovery was not initiated in a timely and coordinated manner, resulting in a high descent rate and a pronounced sideslip at touchdown. The left wing struck the ground, causing structural damage.
Conclusions
The investigation concluded that: the crew was fit for flight; the glider had a valid airworthiness certificate; the instructor initiated a slip to steepen the approach; recovery from the slip was delayed; the glider landed with a high descent rate and in a sideslip, causing the left wing to strike the ground and become damaged; no injuries occurred.
The probable cause was determined to be landing with a high descent rate in a sideslip, likely due to late recovery from the slip.