What happened
On April 1, 2017, an AL600 JASMINE ultralight aircraft, registration OK-UUL23, crashed near the village of Dub, Czech Republic. The aircraft was performing a low-altitude flight, estimated to be between 50 and 100 meters above the ground, when witnesses observed the aircraft's structure beginning to separate during flight.
Observers reported seeing the left wing detach from the fuselage, followed by a trail of light-colored smoke originating from the side of the broken wing. The aircraft descended at a steep angle and struck the ground, where it immediately caught fire. The pilot, who was not wearing a seatbelt at the time of the impact, sustained fatal injuries due to polytrauma and died at the scene. The aircraft was destroyed by the impact and the subsequent fire.
The investigation
The ÚZPLN investigation focused on the structural integrity of the aircraft and the circumstances leading to the in-flight breakup. The aircraft, a prototype version of the Legend 540, was a composite construction. Investigators examined wreckage, including the left wing and control linkages.
Technical analysis of the left wing control rod revealed a fracture caused by extreme loading, though no signs of fatigue or material defects were found. However, the investigation identified significant deficiencies in the manufacturing process, specifically regarding the adhesive bonding of the wing. Furthermore, traces of the pilot's blood were found on the underside of the left wing, though the cause of this biological contamination remained undetermined.
Engine analysis showed that the Rotax 912 ULS engine was not running at the moment of impact and had not suffered a sudden mechanical failure during flight. The aircraft's emergency parachute system (GRS) was found to be functional but was not activated by the pilot during the descent; the deployment was only triggered later by the intense heat of the post-crash fire.
Findings
- The primary cause of the accident was the in-flight destruction of the aircraft, which may have been triggered by one of several factors:
- A structural failure of the wing caused by improper manufacturing and adhesive bonding technology.
- The pilot exceeding the aircraft's flight envelope, potentially inducing flutter.
- An unintentional excursion beyond flight limits caused by the pilot's distraction while attempting to secure a navigation tablet.
- The aircraft suffered from manufacturing defects related to the adhesive bonding of the composite structure.
- The pilot was not restrained by a seatbelt during the critical phase of flight.
- The engine was operational prior to the structural failure and did not experience a sudden stoppage.