What happened
On July 31, 2020, at 13:06 UTC, a training tow operation commenced from Michałków airfield. The flight involved a Socata MS893E Rallye, registration SP-TVG, acting as the tug aircraft, and an SZD-51-1 Junior glider, registration SP-3427. The crew of the tug aircraft consisted of an instructor and a trainee pilot performing glider towing instruction.
The flight proceeded normally until the tug crew initiated a change in circling direction from left to turns to right. During this maneuver, the crew felt a sudden jerk and observed the glider descending rapidly to the left.
According to the glider pilot, the towline became excessively slack at an altitude of approximately 450 meters. In an attempt to tension the line, the pilot deployed the airbrakes. This action caused the towline to catch on the glider's wing. As the line tightened, it moved toward the center of the wing and became entangled with the airbrake plate. The tension caused the towline to be severed by the edge of the airbrake plate, which also resulted in the plate being bent. Because of the entanglement, the pilot was unable to retract the airbrakes. Facing a rapid loss of altitude, the pilot executed an emergency landing in an unprepared field. The landing was completed without major disruption, despite a slight deviation in direction during the final rollout.
The investigation
The PKBWL examined the sequence of events, the mechanical state of the SZD-51-1 Junior, and the pilot's actions during the loss of tension. The investigation focused on the cause of the line slackening and the subsequent mechanical failure of the airbrake mechanism caused by the towline entanglement.
Findings
- The primary cause of the incident was pilot error involving improper flight technique, specifically allowing the towline to become excessively slack.
- The pilot's attempt to tension the slack line by using the airbrakes was performed incorrectly, leading to the entanglement.
- Contributing factors included significant turbulence and wind gusts during the flight.
- The glider pilot lacked sufficient recent training, as this was only their third towed flight of 2020 and their first solo towing operation.
- The aircraft sustained minor damage, including a bent airbrake plate and slight delamination of the trailing edge, which was subsequently repaired.