What happened
On May 18, 2011, a SportStar RTC aircraft, registration OK-EAK, was performing approved flight testing near Kunovice, Czech Republic. The mission involved verifying the aircraft's flight characteristics and behavior during various spin configurations. The pilot had successfully completed approximately 35 spins in various configurations before attempting a final maneuver to test the aircraft's behavior in a right spin at idle power and closed flaps.
During this maneuver, the pilot executed a steep left turn just below FL 70. Following the turn, the aircraft lost airspeed and entered a right spin. The pilot attempted recovery maneuvers, including applying left rudder and reducing elevator input, but the aircraft failed to recover. Instead, the rotation accelerated around the vertical axis. During the intensified rotation, the engine stopped running.
Recognizing the loss of control, the pilot deployed the aircraft's ballistic parachute system. The parachute successfully deployed, though the aircraft continued to rotate on the lines before eventually descending into a lake southwest of Kunovice Airport. The pilot survived the impact by swimming to shore, though the aircraft was submerged in approximately nine meters of water.
The investigation
An investigation by the ÚZPLN focused on the aircraft's control surfaces and the pilot's actions. Investigators examined the rudder assembly and found an asymmetry in the rudder deflections; the right deflection had increased from 31° to 36.5°, while the left deflection had slightly decreased. Analysis of the "Nicopress" cable fasteners showed they had shifted, which could have affected the control linkage.
Technical examination of the rudder also revealed deformation. It was determined that the rudder was not effective during the critical phase, likely due to aerodynamic stall on the surface caused by the asymmetric deflection. The investigation also considered the pilot's physiological state, noting that the pilot had already completed an eight-hour work shift prior to the critical flight and was performing repetitive, high-concentration tasks to record flight parameters.
Findings
- The pilot was qualified for the flight but lacked specific experience in verifying the flight characteristics of this particular aircraft type during spin testing.
- The pilot's concentration may have decreased due to the repetitive nature of the testing and the fatigue from a long duty day.
- The primary cause of the critical situation was the pilot's decision to perform a maneuver outside the formal test program, which resulted in an unexpected and unrecoverable flight condition.
- An asymmetric rudder deflection likely caused an aerodynamic stall on the rudder, rendering it ineffective for recovery.
- The engine failure occurred as a direct result of the intensified rotation.