On August 16, 2015, a L-23 Super Blaník (registration OK-0214) was involved in an aviation accident near LKMI, CZ. No fatalities were reported. Investigators recorded the probable cause as: Loss of speed during a winch launch interruption, exacerbated by an unexpected tailwind gust, leading to a hard landing and left-wing contact with the ground. This summary draws on records from the Czech Air Accidents Investigation Institute (UZPLN).
On 16 August 2015, a glider L23 Super-Blaník, registration OK-0214, operated by Aeroklub Jeseník, o.s., suffered a hard landing and left-wing contact with the ground at Mikulovice airfield (LKMI) during a winch launch training exercise.
Overview and Investigation Context On 16 August 2015, the Czech Institute for the Investigation of Causes of Aircraft Accidents (ÚZPLN) received a report concerning an accident involving a two-seat glider, L23 Super-Blaník, registration OK-0214, at Mikulovice airfield (LKMI). The aircraft was owned and operated by Aeroklub Jeseník, o.s. The investigation was conducted in accordance with EU Regulation 996/2010, Czech Act No. 49/1997 on Civil Aviation, and Annex 13 to the Chicago Convention. Its purpose was solely to prevent future accidents and incidents, without assigning blame or liability. The final report was issued on 17 February 2016. ## Aircraft and Personnel The aircraft was a LET L23 Super-Blaník, a two-seat, all-metal, high-wing glider designed for basic glider pilot training. It was manufactured in 1990, with serial number 907617, and had a total time of 2,221 hours 07 minutes and 3,485 takeoffs. Its airworthiness certificate and legal insurance were valid. No onboard recording device was installed. The crew consisted of a 46-year-old male glider flight instructor holding a valid GLD/FI(G) rating and a Class 2 medical certificate, with 737 hours 29 minutes of glider experience. The student pilot was a 52-year-old male who had begun glider training on 28 October 2014 and had accumulated 14 hours 57 minutes of glider time by the date of the accident. He had completed six flights with the same instructor prior to the critical flight. No injuries were reported. ## Flight Sequence and Contributing Factors The accident occurred during a winch launch training exercise focused on emergency procedures, specifically a winch tow interruption below 50 meters above ground level (AGL). The student pilot was on his seventh launch of the day and was nearing the completion of his training. The launch took place from the grass runway 23 at LKMI. According to the instructor, the glider achieved lift-off speed and entered the transition arc, where the winch tow was interrupted. The student initially responded correctly by pushing the control stick forward to maintain speed. However, as the glider transitioned into a glide, the student attempted to level the aircraft. At that moment, an unexpected tailwind gust caused a loss of speed. The left wing and main landing gear contacted the ground, resulting in a hard landing. The glider veered off the runway and came to rest approximately 150 meters after leaving the runway, about 550 meters from the launch point. The winch operator, a 70-year-old male with extensive experience, stated that the winch and tow rope were functioning normally. He interrupted the tow at approximately 30 meters AGL, lower than in previous launches, to save time. He noted a slight tailwind of up to 2 m/s at the time of launch and did not consider it a problem. He observed a delay of less than one second in the crew's response to the tow interruption, followed by a sharp push forward that directed the glider steeply toward the ground. He believed the instructor may have intervened in the controls, but the instructor later confirmed that control remained with the student. ## Damage and Meteorological Conditions The accident caused extensive damage to the glider, including deformation and cracking of the rear lower fuselage skin near the main landing gear, deformation of the lower longitudinal spar, and damage to the left wing. The left wing's upper and lower outer spars were broken at rib 25, the skin between ribs 19-25 and 25-31 was deformed, and the left aileron was broken. The main landing gear and its attachment points were also deformed. Meteorological conditions at the time of the accident, as estimated by the Czech Hydrometeorological Institute, included variable winds of 4-8 knots at ground level, a wind of 130°/05 kt at 2,000 ft AGL, visibility over 10 km, and few cumulus clouds with a base at 3,500-4,000 ft AGL. A slight cold front was present over the Czech Republic but did not affect the accident area. ## Safety Recommendations The report does not explicitly list specific safety recommendations in the provided text, but the investigation highlighted the importance of proper speed management during winch launch interruptions and the potential impact of tailwind gusts on glider performance. The crew's response to the tow interruption was noted as initially correct but insufficient to maintain adequate speed during the transition to glide, particularly in the presence of an unexpected tailwind gust.
Probable cause
Loss of speed during a winch launch interruption, exacerbated by an unexpected tailwind gust, leading to a hard landing and left-wing contact with the ground.