Factual Information
On 25 August 2017, at 13:40 UTC, a motor glider L-13 SE Vivat, registration OK-8118, operated by Aeroklub Frýdlant nad Ostravicí, was conducting training flights at Frýdlant airfield (LKFR). The crew consisted of an instructor and a student pilot. They completed a series of three takeoffs and full-stop landings. After the third landing, while taxiing to the holding point for runway 26, the main landing gear collapsed forward. The crew shut down the engine and evacuated without injury. Inspection revealed a fractured folding strut of the main landing gear and damage to the lower fuselage.
The instructor reported that all landings were normal. The student stated that during slow taxi, about 100 meters before the holding point, the aircraft sank and stopped. The police conducted a breathalyzer test on the crew with negative results.
Crew Information
The instructor, aged 67, held a valid SPL for gliders and TMG class, with a total flight experience of 1564 hours 59 minutes, including 1404 hours 59 minutes as PIC and 156 hours 17 minutes on type. The student pilot, aged 42, held a valid glider pilot license with a total of 99 hours 57 minutes, including 69 hours 16 minutes as PIC and 3 hours 40 minutes on type.
Aircraft Information
The L-13 SE Vivat is a two-seat metal motor glider with retractable main landing gear. The aircraft was manufactured in 1998 (serial number 880304) by EVEKTOR Aerotechnik. Total time in service was 2768 flight hours and 8630 landings. The latest 400-hour inspection was performed on 17 January 2014. The aircraft had a valid certificate of airworthiness and maintenance release. Weight and balance were within limits.
Meteorological Conditions
Weather conditions were suitable for training: visibility over 10 km, surface wind variable at 4 knots, scattered cirrus and stratocumulus clouds at 4/8 coverage.
Damage
The main landing gear folding strut fractured, causing the gear to fold forward. The wheel and strut damaged the lower and side fuselage, including the laminate skin and truss structure in the area of control attachments.
Analysis
The investigation relied on crew statements, police report, photographs, and information from the maintenance organization. The crew was qualified and medically fit. The airfield was operational and its surface condition did not contribute. The folding strut failed due to a fatigue fracture at a point where the cross-section changes, a location subject to high stress during gear extension and retraction as well as during taxi over uneven surfaces. Maintenance and operation were in accordance with manufacturer requirements; no pre-existing defects were recorded.
Conclusions
- The pilots were qualified and held valid medical certificates.
- The motor glider had valid certification and operational documentation.
- No exceedance of operational limits during the training flights or ground movement was found that could have caused the strut fracture.
Probable Cause: Fatigue fracture of the landing gear extension strut during taxiing.
Safety Recommendations
No safety recommendations were issued by the investigation authority.