What happened
On June 17, 2009, at 11:52 UTC, a military L-159 ALCA (registration/serial number 6055) was performing a 360-degree climbing turn to 5,200 ft AMSL within the TRA 54/84 temporary reserved airspace. During this maneuver, the pilot was focused on reviewing onboard systems and receiving new task instructions.
At approximately 11:52:25 UTC, the pilot spotted an unidentified glider directly ahead of the aircraft at an extremely close distance, estimated between 30 and 50 meters. The pilot immediately interrupted the task, notified the Náměšť nad Oslavou approach controller (APP LKNA), and performed evasive maneuvers to avoid a collision and prevent the creation of turbulence that might affect the glider. While the pilot attempted to visually identify the aircraft, the glider's registration could not be determined. The glider, likely reacting to the presence of the military jet, subsequently maneuvered and exited the TRA 54 airspace toward the south near Znojmo.
The investigation
The ÚZPLN investigation utilized onboard video footage from the L-159 ALCA's Head-Up Display (HUD) and cockpit camera, which captured the 4.2-second window of the near-collision. Investigators also analyzed primary and secondary radar data from the Brno and Náměšť radar centers.
Radar analysis tracked the unidentified glider's trajectory, showing it had entered the TRA 54 airspace without authorization. The investigation established that the glider was likely not equipped with an SSR transponder, as it appeared only as a primary radar target. The glider was described by the pilot as a modern, high-performance model equipped with winglets.
Findings
- The unauthorized entry of the unidentified glider into the controlled airspace was the primary cause of the incident.
- The pilot of the glider demonstrated insufficient vigilance regarding the restricted airspace requirements.
- The pilot of the L-159 ALCA had a limited ability to monitor the surrounding airspace at the moment of the encounter due to the high concentration of attention required for system checks and task transitions.
- The glider crossed the flight path of the military aircraft at the same altitude (5,200 ft AMSL), creating a high risk of collision.