What happened
On April 11, 2004, an amateur-built ULLa Kosák 3, registration OK-JUE 01, was conducting a demonstration flight for a prospective student near Hořovice. Shortly after departing from runway 07 at Hořovice airfield, the pilot began performing maneuvers at a low altitude, approximately 100 meters above the ground, in the area between Kotopeky and Praskolesy.
During a sharp 270-degree left turn involving a steep descent, the aircraft entered a steep climb. During this phase of flight, the engine likely failed. Due to the low altitude and the loss of airspeed following the engine failure, the pilot was unable to maintain sufficient control or establish a glide slope for a safe landing. The aircraft entered a rapid descent and struck the ground, resulting in the total destruction of the aircraft. The pilot and the passenger sustained injuries.
The investigation
The ÚZPLN investigation examined the aircraft's technical configuration and the flight conditions. The aircraft was powered by a modified Škoda Favorit automobile engine. Investigators analyzed the fuel system, specifically the placement of the diaphragm fuel pump and the carburetor. The investigation also reviewed the aircraft's weight and balance, noting that the takeoff weight of 496 kg exceeded the maximum allowable limit by 46 kg.
Findings
- The primary cause of the accident was the execution of maneuvers at a low altitude, which left no margin for error following the engine failure.
- The engine failure was likely triggered by the aircraft's technical configuration; the orientation of the engine and carburetor relative to the aircraft's longitudinal axis caused inertial forces to affect the carburetor float valve. This led to insufficient fuel delivery during steep turns and climbs.
- The placement of the fuel pump relative to the fuel tank (with a suction head exceeding 800 mm) further reduced the pump's efficiency.
- The pilot's inability to manage the emergency landing was compounded by the aircraft being overweight by 46 kg and the presence of a tailwind during the attempt.
- The use of a three-blade composite propeller was noted as being inconsistent with the aircraft's registration documents.