What happened
On November 8, 2016, at approximately 14:30 UTC, a Bristell NG 5 Elsa, registration OK-VAR 03, was performing a critical training flight near the villages of Brodce and Luštěnice, Czech Republic. The flight, operated by Aeroklub Praha Letňany, z.s., was part of a training syllabus involving an instructor and a student.
During the flight, the aircraft performed various maneuvers involving changes in direction, altitude, and airspeed. Air traffic control records indicated that the aircraft's visibility on radar was intermittently lost during these maneuvers. A witness observing the aircraft from a nearby road reported seeing the ultralight in an uncontrolled, irregular spin at an altitude of approximately 200 to 250 meters. The aircraft was rotating rapidly around its vertical axis with the nose pitched down at an angle of roughly 45 degrees.
Shortly after the witness observed the spin, the aircraft impacted a dense forest area in the Josefov woodland. The impact was followed by a post-crash fire that heavily damaged the airframe. Both occupants of the aircraft sustained fatal injuries and died at the scene.
The investigation
Investigators from the ÚZPLN and the Czech Light Aircraft Association (LAA ČR) examined the wreckage and recovered components. The investigation focused on the mechanical condition of the Bristell NG 5 Elsa, the engine performance, and the meteorological conditions at the time of the accident.
Examination of the wreckage showed that the aircraft's control surfaces, including the ailerons, elevators, and rudder, were intact and functional. The engine, a Rotax 912 ULS, showed no evidence of a sudden, violent stoppage during flight. Analysis of the propeller suggested that the engine was likely at idle or not running at the moment of impact. The investigation also considered the possibility of carburetor icing, as the ambient temperature and humidity levels were conducive to ice formation in the intake if the carburetor heat was not properly utilized.
Findings
- The primary cause of the accident was the failure to recover from an uncontrolled spin at a low altitude.
- The exact trigger for the initial loss of control could not be determined, as the investigation could not definitively establish the cause of the situation that led to the spin.
- Meteorological conditions, specifically the potential for carburetor icing due to high humidity and low temperatures, could have led to a loss of engine power.
- The possibility of spatial disorientation following entry into cloud cover was considered a contributing factor.
- The aircraft was within its permitted weight and center of gravity limits at the time of the accident.