What happened
On October 24, 2009, at approximately 11:30 UTC, an amateur-built Cora D-Allegro ultralight aircraft, registration OK-EUO 01, crashed into the summit of Písečný vrch near the village of Milá, Czech Republic. The aircraft was performing a recreational VFR flight, having departed from the Charvátce airfield roughly 90 minutes prior to the accident.
Witnesses on the hilltop observed the aircraft approaching from the north. During a wide turn over the summit, the aircraft appeared to be flying at a very low altitude, estimated at approximately 50 meters. Eyewitnesses reported seeing the right wing lift upward at a nearly 90-degree angle relative to the fuselage, immediately followed by a steep, direct descent. The aircraft struck the ground approximately 100 meters from the observers, resulting in the destruction of the aircraft and the fatal injury of the pilot.
The investigation
The ÚZPLN investigation examined the wreckage and interviewed witnesses. The investigation focused on the aircraft's flight characteristics, specifically its use of flaperons for lateral control. Investigators analyzed the structural integrity of the wing-to-strut connection and the installation of safety equipment.
While the investigation identified several construction and maintenance deficiencies in the aircraft—including improper material selection for the center section, hidden corrosion, and substandard installation of the wing strut pin—the commission ruled out structural failure of the wing connection as the cause of the accident. Furthermore, the investigation found that the seatbelt installation was non-compliant with airworthiness requirements, featuring a weakened seam that failed during the high-G deceleration of the impact.
Findings
- The pilot was performing a maneuver involving the flaperons at a very low altitude.
- The use of significant downward flaperon deflection likely induced an aerodynamic stall on the right wing, causing a sudden loss of lift and an unexpected roll.
- The pilot's limited experience on this specific aircraft type (having only 6:46 hours of flight time on the Cora D-Allegro) likely prevented an adequate recovery response.
- The aircraft was flying below the required minimum altitude of 150 meters above the terrain.
- The pilot initiated a maneuver that caused an unexpected loss of lift at low altitude.