What happened
On September 25, 2016, at 15:10 UTC, a Blanik BL-23 glider, registration S5-7104, was conducting a VFR training flight at Lesce Airport (LJBL), Slovenia. The flight began as a towed operation to maintain flight qualifications. After releasing from the tow aircraft, the pilot proceeded to glide northeast of the airport. Due to poor thermal conditions, the pilot decided to return to the airfield.
While attempting to enter the northern school circuit, the pilot realized the aircraft was at an insufficient altitude to reach the main runway. In an attempt to perform an emergency landing, the pilot selected a grassy area used for model aircraft activities. During this maneuver, the left wing of the glider struck the ground, followed by the nose of the fuselage. The impact caused the aircraft to rotate 180 degrees vertically. The pilot and the passenger escaped the aircraft without injuries, but the Blanik BL-23 was destroyed and beyond repair.
The investigation
The investigation examined the pilot's flight preparation, altitude references, and the airfield's operational procedures. Investigators reviewed the pilot's documentation, noting that while the pilot held valid licenses and a medical certificate, there was no evidence of continuous maintenance of glider flight qualifications during 2016.
The investigation also analyzed the altimeter settings. It was determined that the pilot likely misinterpreted the altimeter setting, using QNH (altitude above mean sea level) instead of QFE (altitude above field elevation). Because the airport elevation is 504 m, the pilot believed the aircraft was at 600 m when it was actually only approximately 100 m above the ground. Furthermore, the investigation reviewed the airport's manual, finding that it lacked sufficient guidance regarding suitable landing sites for emergency operations.
Findings
- The pilot misjudged the actual altitude above the terrain due to an incorrect interpretation of the altimeter setting.
- The pilot's decision to land on the model aircraft field was risky due to the presence of people and obstacles in the immediate vicinity.
- The pilot had not maintained continuous flight qualifications in the glider category.
- The pilot lacked sufficient knowledge of the local terrain and the specific glider procedures outlined in the airport manual.
- The direct cause of the accident was the impact of the glider with the ground during an attempt to land on a grassy field used for unmanned aerial vehicles.