What happened
On October 24, 2022, a TL2000 STING S4 ultralight aircraft, registration OK-KUU 81, was conducting a functional check of its navigation equipment prior to delivery to a customer. The flight, which originated from Hradec Králové, involved a pilot and a passenger from the aircraft manufacturer.
According to ADS-B radar data, the aircraft climbed to 3,40 and then began a period of low-speed flight, likely to test the stall warning system. During this phase, the ground speed dropped to approximately 62 knots. While the aircraft was at a lower altitude, the pilot increased engine power, causing a brief increase in speed, but the aircraft subsequently slowed to 50 knots. This led to a sudden loss of control and a rapid descent. The aircraft entered a spin, characterized by a sharp change in heading and a rapid loss of altitude. The aircraft impacted the ground near Vlčkovice v Podkrkonoší and caught fire. Both the pilot and the passenger sustained fatal injuries.
The investigation
The ÚZPLN investigation focused on analyzing ADS-B radar data and witness testimony. A witness observed the aircraft falling vertically and rotating around its longitudinal axis. The investigation confirmed that the aircraft's engine was functioning at the time of impact, as evidenced by the position of propeller blades at the crash site.
Technical examination of the wreckage showed that the aircraft was structurally intact upon impact and no mechanical failures were identified. The flight control surfaces were functional, and the damage observed was a result of the impact and the subsequent fire. The investigation also noted that although the aircraft was equipped with a Magnum 601 ballistic parachute recovery system, the pilot did not attempt to activate it during the critical phase of the flight.
Findings
- The primary cause of the accident was the loss of control at low airspeed, which resulted in the aircraft entering an unrecoverable spin.
- The pilot lacked practical experience in recovering from a spin.
- Meteorological conditions, including cloud cover that obscured the natural horizon and strong 26-knot winds, likely complicated the pilot's ability to maintain orientation during the low-speed test.
- The aircraft was not found to be exceeding its maximum takeoff weight.
- The manufacturer's organization lacked established procedures for documenting the specific purposes and planned profiles of such test flights.