What happened
On March 18, 2012, an instructor was conducting training flights with a group of student pilots using an SZD-50-3 Puchacz glider at Piotrków Trybunalski Airport (EPPT). The flights were being conducted using a WS-01-JK type winch on a heading of 210°.
During one of the flights, after reaching an altitude of approximately 280 meters and following the cessation of winch tension, the student pilot attempted to release the cable by releasing the stick and pulling the release mechanism three times. The winch operator notified the crew via radio that the cable had not been released. The instructor took control of the aircraft and attempted further release attempts without success. To manage the situation, the instructor executed a 180-degree left turn, increasing the airspeed to approximately 130 km/h.
In an attempt to resolve the situation, the winch operator activated the pneumatic guillotine to sever the cable, but the mechanism failed to function. The operator then reduced the engine speed to a minimum and made another attempt to cut the line, which also failed. Only after the operator shut down the engine was the cable able to unwind freely. The crew felt a sudden jerk and an increased rate of descent caused by the drag of the trailing cable. While flying in a steep bank, the glider lost altitude rapidly. The pilot leveled the aircraft and landed on the main wheel just a few meters above the ground. The landing roll was limited to approximately 10 meters due to the continued drag from the unsevered cable. No injuries were sustained, and the aircraft remained undamaged.
The investigation
The investigation examined the release mechanism and the winch equipment. Following the incident, the release hook and the entire release system were disassembled and inspected, revealing no operational malfunctions. However, a subsequent inspection of the release force was conducted at a certified glider workshop in Jeżów Sudecki. This inspection revealed that the release force was factory-set at the upper limit of the allowable tolerance.
Findings
- The primary cause of the failure to release was that the glider's release hook force was set at the maximum allowable factory tolerance.
- The pneumatic guillotine on the winch failed to operate correctly during the emergency.
- The engine shutdown was the necessary action that allowed the cable to finally unwind.