What happened
On May 15, 2015, at approximately 14:12, a JS-1C glider, registration ZG-GBT, was performing a training flight at the Turbia airfield in preparation for the Polish Open Class Glider Championships. The aircraft was being towed by a PZL 104 Wilga. This particular flight was the pilot's first time operating the JS-1C with full water ballast, resulting in a high takeoff weight of approximately 720 kg.
During the takeoff roll, the glider lifted off in a two-point configuration with a high angle of attack. Following separation from the ground, the glider began to oscillate between left and right wings and drifted laterally from the tow plane's path. At an altitude of approximately 50 meters, the glider climbed above the tow plane and entered a steep right bank of about 80 degrees. The pilot of the tow plane attempted to maneuver to maintain the tow, but the glider's flight became increasingly unstable. The glider pilot eventually released the tow cable at an altitude of about 100 meters. While attempting a 180-degree turn back toward the airfield, the glider entered a dynamic stall, resulting in an autorotative spin that caused the aircraft to strike a group of trees. The impact destroyed the tail boom and wings, and the forward fuselage struck the ground inverted. The pilot sustained serious injuries.
The investigation
The PKBWL investigation utilized CCTV footage from the Aeroklub Stalowa Wola to reconstruct the flight sequence. The investigation examined the aircraft's technical configuration, specifically the flap and landing gear settings. Investigators found the flap lever set to position 2 (0°), whereas the pilot believed he had moved them to position 4 (+13.5°) to assist takeoff. Additionally, while the pilot stated he did not retract the landing gear during the tow, investigators noted the gear lever was found in the retracted position, suggesting it may have been moved during the crash or rescue efforts.
Findings
- The primary cause of the accident was the unstable flight of the glider during the tow.
- The pilot executed a 180-degree turn at an altitude of less than 100 meters, which led to a dynamic stall.
- The pilot's lack of experience operating a glider with such high wing loading (over 58 kg/m²) contributed to the inability to stabilize the aircraft.
- The use of a tow cable shorter than the length recommended in the JS-1C Pilot's Operating Handbook (35-40 meters instead of the recommended 50-80 meters) was a contributing factor.