What happened
On October 31, 2015, an L-13A Blaník, registration OK-9707, was performing a training flight at Hosín Airport (LKHS). The flight was part of a training syllabus for a student pilot, accompanied by an instructor, specifically practicing landings into a restricted area. The day's operations involved winch launching, with the flight pattern adjusted to account for winds between 12 and 16 knots from the east-southeast.
During the third flight of the session, the aircraft was on final approach to runway 12. As the glider descended, the descent angle decreased at approximately 30 meters. Upon entering the boundary layer at an altitude of roughly 15 to 20 meters, the aircraft encountered unexpected wind effects, causing a sudden drop in airspeed. At approximately 10 meters above the ground, the glider stalled. The pilot and instructor reacted too late to the loss of airspeed, resulting in a hard landing without a flare. The impact caused significant structural damage, including deformation of the fuselage skin near the center section, damage to the main landing gear attachment, and deformation of the floor in the rear cockpit area. No injuries were reported.
The investigation
The ÚZPLN investigation examined the flight sequence, the meteorological conditions, and the aircraft's maintenance status. The investigation reviewed testimonies from the instructor, the pilot, and a witness, as well as the aircraft's maintenance records. The investigation established that the weather conditions were suitable for the intended flight activities and that both crew members held valid licenses and medical certificates. The aircraft was found to be airworthy with valid maintenance documentation.
Findings
- The primary cause of the accident was the delayed reaction of the crew to the changing wind effects on the glider during the approach.
- The aircraft encountered a sudden loss of airspeed due to the influence of the boundary layer at low altitude.
- The crew failed to timely increase the angle of attack or apply airbrake to compensate for the loss of speed.
- The aircraft sustained extensive structural damage to the underside of the fuselage, the center section, and the landing gear components.