What happened
On June 11, 2017, at 12:48 UTC, an ASW 20 CL glider, registration OK-8709, was involved in an accident on the northern edge of the village of Bystré, near Svitavy. The pilot was conducting a cross-country thermal flight. After the first two legs of the flight, thermal conditions significantly deteriorated near the Vír reservoir.
Having identified a suitable field for an off-field landing, the pilot performed a reconnaissance turn at approximately 1,000 m AMSL. However, instead of proceeding directly to the landing site, the pilot continued to search for rising air currents in the vicinity. After failing to find any lift, the pilot decided to return to the previously selected field.
During the approach on a heading of approximately 200°, the pilot initiated a 360-degree right-hand turn at an altitude of roughly 70 m AGL. During this maneuver, the aircraft lost significant altitude and drifted over a residential area. At approximately 8 m AGL, the right wing struck the top of a tall tree, severing a portion of the wing and breaking the tree trunk. The impact caused the glider to deviate sharply from its flight path, striking the ground nose-first before flipping onto its back. The pilot sustained serious injuries and was hospitalized following surgery.
The investigation
The ÚZPLN investigation examined the flight data recorder, the pilot's experience, and the aircraft's maintenance history. The investigation established that the pilot was fully qualified with a valid medical certificate and significant flight experience on this aircraft type. The ASW 20 CL was also found to be airworthy, with its last annual inspection completed in October 2016. Meteorological data confirmed that while conditions were partly cloudy with light winds, the primary issue was the lack of sufficient thermal lift to maintain altitude during the low-level maneuvering.
Findings
- The pilot performed a landing maneuver with insufficient clearance above obstacles.
- The pilot failed to correctly estimate the required altitude for the landing maneuver.
- The pilot did not maintain a safe altitude above obstacles while searching for thermals.
- The primary cause was the late termination of the cross-country thermal flight, leading to maneuvering too low to the ground in an attempt to find rising air.