What happened
On July 23, 2019, at approximately 18:06 LMT, an SZD-50-3 Puchacz glider, registration SP-3352, was performing a winch-assisted training flight at Piotrków Trybunalski Airport (EPPT). The flight was part of a basic training program for a student pilot, conducted by an instructor. The specific objective of the flight was to practice emergency procedures (SPL/I-4 tasks).
Prior to the launch, the crew and the winch operator had agreed upon a specific signal to simulate an emergency: the instructor would repeatedly press the radio transmit button to signal the operator to reduce winch tension. During the climb, at an altitude of approximately 20–30 meters, the winch operator heard radio interference from other aircraft operating in the area. He mistook this interference for the agreed-upon signal and reduced the winch speed, effectively aborting the launch.
Following the reduction in tension, the glider continued to climb briefly with the towline still attached. The crew did not immediately release the line. As the glider lost airspeed, it entered a steep descent. In an attempt to maintain control at a very low altitude, the instructor pulled back sharply on the control stick, which induced a stall and triggered a left-hand autorotation. The glider struck the ground with its left wing, followed by the main landing gear.
Both the instructor and the student pilot sustained serious injuries.
The investigation
The PKBWL investigation established that the aircraft was airworthy, the crew was properly licensed, and the weather conditions were suitable for flight. The investigation focused on the sequence of events following the winch operator's decision to reduce tension. Analysis of witness statements and surveillance footage confirmed that the crew's reaction to the loss of tension was delayed, and the glider remained attached to the towline for a period after the winch speed had decreased.
Findings
- The primary cause of the accident was the delayed reaction of the instructor to the loss of winch tension.
- A contributing factor was the established communication method, where pressing the radio transmit button was used as a signal, which created ambiguity.
- The winch operator's decision to abort the launch was triggered by the misinterpretation of radio interference as the agreed-upon signal.
Safety action
Following the accident, the following preventive measures were implemented by the operator:
- Conducting full debriefings of the event with flight instructors, students, and winch mechanics.
- Requiring winch mechanics to use headphones and refrain from interrupting tension unless there is absolute certainty.
- Ensuring that simulated emergency training is explicitly discussed and understood by all parties before the flight.
- Mandating that simulated emergencies be initiated by a clear radio command: "winch abort, winch abort."
- Prohibiting the use of repeated radio button presses as a method to initiate simulated emergencies.