What happened
On July 11, 2003, at approximately 16:00 UTC, an amateur-built Asso 5 ultralight aircraft, registration OK-EUO, crashed into a sugar beet field near Postoloprty, Czech Republic. The flight had departed from Tánec Macerka airport earlier that afternoon with the pilot and one passenger.
While flying over the Postoloprty area, the aircraft experienced engine instability followed by a complete engine failure. Simultaneously, the pilot encountered severe difficulties with the longitudinal flight controls. In an attempt to avoid built-up areas, the pilot maneuvered the aircraft toward an open field north of the town. During the descent, the pilot attempted to extend the landing gear, but the gear remained partially retracted. The aircraft struck the ground in the beet field with significant force, causing the total destruction of the airframe. The impact caused the nose of the aircraft to rotate upward, leaving the nose gear pointing into the air.
The investigation
The ÚZPLN investigation focused on the mechanical failures and the sequence of events leading to the impact. Technical examinations of recovered components included the control lever assembly, the throttle linkage, and the airspeed indicator.
Investigators examined the engine's carburetor throttle linkage and found evidence of a fatigue fracture in the drive shaft of the right cylinder group. Furthermore, the investigation looked into the longitudinal control system, specifically the welded joint of the dual control lever. While the investigation could not definitively confirm a failure at the weld due to the high-energy inputs during the emergency, deformations were noted in the control surface linkages.
Findings
- The primary cause of the accident was the failure of the longitudinal flight control system.
- An engine failure occurred during flight due to a fatigue fracture in the throttle linkage drive shaft.
- The engine failure placed the pilot under intense stress, leading to energetic and forceful inputs on the flight controls.
- The partial extension of the landing gear significantly contributed to the structural deformation of the aircraft upon impact.
- The pilot sustained fatal head injuries due to the rapid forward movement of the upper body caused by inertia, while the passenger escaped with minor injuries.