What happened
On October 30, 2009, at 13:34 UTC, a LOT Polish Airlines Embraer ERJ145, registration SP-LGE, was performing an approach to runway 06 at Prague/Ruzyně (LKPR). Simultaneously, a Cessna 172, registration OK-JAS, was conducting a VFR flight from LKLN to LKSZ.
At approximately 12:30 UTC, the Cessuna 172 entered the Prague TMA II controlled airspace at 3,700 ft without establishing two-way radio communication with Prague Approach. As the Embraer ERJ145 was cleared to descend through various altitudes for its approach, the two aircraft converged. At 12:35 UTC, the crew of the Embraer ERJ145 reported a TCAS RA (Resolution Advisory), prompting a climb to 4,400 ft. At the moment of the TCAS alert, the horizontal separation had decreased to 0.6 NM and vertical separation to only 400 ft.
The investigation
The ÚZPLN investigation examined radar data, air traffic controller (ATCo) statements, and pilot testimonies. The investigation focused on why the unauthorized aircraft was not detected by the controller and why the automated warning systems failed to alert the staff.
Investigators analyzed the E2000 radar system's performance, specifically the 'NONC' warning function designed to highlight unauthorized traffic. The analysis revealed that the controller did not register the Cessna 172 due to poor target resolution (a dark blue target against a grey background) on the display. Furthermore, the investigation found significant deficiencies in the implementation of the radar's warning features, including a lack of safety analysis and a failure to establish a proper methodology for the warning area parameters.
Findings
- The primary cause of the loss of separation was the unauthorized entry of the Cessna 172 into the Prague TMA II.
- The air traffic controller failed to notify the crew of the Embraer ERJ145 regarding the presence of the unidentified aircraft.
- The radar's 'NONC' warning function failed to alert the controller to the airspace penetration.
- The pilot of the Cessna 172 entered the controlled airspace without establishing radio contact and failed to maintain adequate situational awareness regarding their altitude.