What happened
On October 29, 2020, a Shark UL ultralight aircraft, registration F-JCEC, was conducting a VFR flight from Poland to France. While climbing through FL105 within the Prague Flight Information Region, the pilot reported engine and speed problems to Air Traffic Control (ATC). Following this report, the aircraft entered a rapid descent, performing a maneuver that likely transitioned into a left-hand spin.
During this steep descent, the aircraft reached a ground speed of 2GS, approximately 270 kt, which significantly exceeded its structural speed limits. The aircraft then leveled off briefly at 4750 ft before continuing a steady descent toward Olšany near Prostějov. Despite being offered nearby suitable airfields by ATC, the pilot elected to continue toward Olomouc. As the aircraft approached the site, the pilot deployed the landing gear. This action, combined with the loss of the horizontal stabilizer, created a massive pitching moment that the pilot could not counteract. The aircraft struck the ground in a field, resulting in the fatal death of the pilot and the total destruction of the aircraft.
The investigation
An investigation by the ÚZPLN examined radar data, meteorological records, and the wreckage of the aircraft. Investigators analyzed the aircraft's flight path, noting a period of extreme high-speed descent. The investigation focused on the structural integrity of the carbon fiber composite stabilizer and the aerodynamic effects of the high-speed maneuver. The team also evaluated the pilot's decision-making process, the presence of icing conditions, and the functionality of the aircraft's emergency recovery system.
Findings
- The aircraft encountered IMC conditions with icing, which impacted engine performance and aircraft controllability.
- The aircraft exceeded its maximum allowable speed (VNE) and the safe flutter boundary, leading to aeroelastic flutter.
- The cyclic stress from flutter caused the structural failure and subsequent loss of the horizontal stabilizer.
- The pilot experienced a loss of situational awareness and spatial orientation under high emotional stress.
- The pilot's decision to extend the landing gear at high speed, while lacking pitch control, contributed to the final loss of control.
- The onboard emergency recovery system was not activated by the pilot prior to the impact.