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 flight levels for its approach, the aircraft closed distance with the unauthorized traffic. At 12:35 UTC, the crew of SP-LGE reported a TCAS RA (Resolution Advisory), prompting a climb to 4,400 ft to avoid a collision. 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 control (ATC) recordings, and pilot statements. The investigation established that the Cessna 172 pilot had entered the controlled airspace without authorization and failed to maintain proper altitude awareness during a local flight inspection.
Investigators also scrutinized the performance of the E2000 radar system. It was found that the ATC controller did not identify the unauthorized traffic due to poor target resolution (a dark blue target against a gray background) and did not relay information regarding the presence of the Cessna 172 to the LOT crew. Furthermore, the investigation revealed significant flaws in the implementation of the 'NONC' warning function, which was intended to alert controllers to unrelated traffic in the TMA. This function failed to trigger, and the investigation found that the function had been implemented without a proper safety analysis or a standardized methodology for defining its operational area.
Findings
- The primary cause of the loss of separation was the unauthorized entry of OK-JAS into the Prague TMA II.
- The air traffic controller failed to notify the crew of SP-LGE about the presence of the unauthorized aircraft.
- The 'NONC' warning function on the radar system failed to alert the controller to the airspace penetration.
- The implementation of the radar warning function lacked a formal safety analysis and a defined operational scope.