Accident Summary
On 28 September 2016, at approximately 13:59 UTC, a VSO-10 glider, registration OK-0581, crashed 500 meters west of the village of Zbyslavec in the Czech Republic. The pilot was seriously injured and transported to a hospital. The glider was substantially damaged. The accident was reported by witnesses to the radio operator at LKPN and the Police of the Czech Republic.
Pilot and Aircraft
The pilot, a 27-year-old male, held a valid SPL (sailplane pilot license) issued in 2006 and a PPL(A) with ratings for MEP land, SEP land, NIGHT, and TOWING-S. He had a total of 71 hours 30 minutes on gliders, with 42 hours 06 minutes solo, and 1 hour 22 minutes in the last 90 days. He also had 318 hours 11 minutes on airplanes. The aircraft was a VSO-10 single-seat, high-wing glider of mixed construction, built in 1980 by Orličan, with serial number 150015. Its total flight time was 2461 hours 45 minutes. The last annual 100-hour inspection was performed on 23 July 2016, with no defects noted. The glider was not equipped with a flight recorder.
Meteorological Conditions
According to the Czech Hydrometeorological Institute, the weather was influenced by a large high-pressure area over Europe, with warm air flowing from the west. At the accident site, surface wind was from 240°–290° at 13–18 knots, gusting to 20–25 knots. Visibility was over 10 km. Cloud cover was few cumulus with base at 4000 ft AGL and top at 6500 ft AGL. Moderate thermal turbulence was reported, and the institute noted that stronger surface winds likely caused mild mechanical turbulence. No significant turbulence was reported at the nearby LKPN airport at 11:45.
Sequence of Events
The pilot arrived at the local Podhořany airfield around 08:00. After completing three aerotows in a motorized aircraft between 10:17 and 12:30, he asked the owner of the VSO-10 for permission to fly it for ridge soaring. The owner towed the glider to about 300 m AGL. The pilot planned to fly southeast toward Sloupno quarry and back, which he did twice without issues. He then flew locally over the main ridge from Podhořany to Lichnice castle ruins, also twice. During the final flight, he was near Zbyslavec at an altitude of about 50–100 m AGL. While initiating a right turn at 160 km/h, he experienced a rapid loss of speed and altitude. After completing the turn, speed dropped to 110–120 km/h and continued decreasing. He felt the glider was being pulled downward by a strong force. He tried to return to the ridge but could not due to the rapid loss of altitude. The glider struck trees at a 45° angle, with the front fuselage impacting the ground. The pilot attempted to avoid a tree by applying left rudder; the cockpit missed the trunk but the fuselage hit a branch, shattering the canopy. The glider then fell through the forest. Witnesses reported seeing the glider fly north to south along the ridge, turn left toward the ridge edge, and then a strong gust prevented it from turning back right, causing it to drift behind the ridge where turbulence was encountered.
Probable Cause
During a right turn, the glider moved beyond the ridge edge, where turbulence caused a rapid loss of speed and altitude. The pilot did not have sufficient height to recover, resulting in impact with trees.