What happened
On June 29, 2017, a G 103 Twin Astir glider, registration OK-1117, was performing a cross-country flight from LKHN to LKFR when it encountered severe atmospheric instability. The flight began as a towed operation using a Z-226 aircraft. After the glider released from the tow at approximately 1,000 m AMSL west of the Ondřejník mountain massif, the pilot climbed to 1,200 m AMSL and began the approach to Frýdlant.
Upon passing the peak of the Ondřejník mountains, the glider entered an area of extreme descending air, with sink rates estimated between 10 and 20 m/s. This rapid loss of altitude made reaching the intended airfield impossible. Seeking a safer landing area, the pilot turned north toward a meadow near a roadway. However, the sustained high sink rate prevented the pilot from reaching a more suitable landing site. During the forced landing attempt, the left wing struck treetops, causing the aircraft to rotate 180 degrees and strike the ground nose-first at a steep angle.
The investigation
The ÚZPLN investigation focused on the meteorological conditions and the pilot's decision-making process. Investigators examined weather data from nearby stations, including Ostrava-Mošnov and Lysá hora, which confirmed significant turbulence and gusty winds in the area. The investigation also reviewed the aircraft's maintenance history, finding that the G 103 Twin Astir had undergone its annual inspection in March 2017 and was airworthy. The pilot, a 48-year-old with extensive experience on the type, was found to be fully qualified and medically fit.
Findings
- The pilot underestimated the wind direction and strength, leading the aircraft into extreme rotor turbulence on the lee side of the mountains.
- The severe descending air currents stripped the pilot of the altitude necessary to reach the planned airfield.
- While the pilot made a correct decision to seek an alternative landing area due to the terrain, the intensity of the sink rate forced an emergency landing on an unsuitable surface.
- The impact with trees and the subsequent nose-first collision with the soft ground resulted in the destruction of the aircraft's forward fuselage and tail section, and caused serious injuries to the pilot.