What happened
On October 30, 2009, at 13:34 UTC, an Embraer ERJ 145, operating as LOT 527, was executing an approach to runway 06 at Prague/Ruzyně (LKPR). During the descent, a Cessna 172 (registration OK-JAS) entered the Prague TMA II controlled airspace at 3,700 ft without establishing two-way radio communication or receiving prior clearance.
As the ERJ 145 continued its descent, the distance between the two aircraft rapidly decreased. At 13:35:35 UTC, the crew of LOT 527 reported a TCAS RA (Resolution Advisory), indicating a collision risk. At the time of the alert, the aircraft were separated by only 0.6 NM horizontally and 400 ft vertically. The pilot of the ERJ 145 responded to the TCAS command by climbing 200 ft to 4,400 ft to maintain safety.
The investigation
The ÚZPLN investigation examined radar data, air traffic control (ATC) recordings, and pilot statements. The investigation focused on why the unauthorized aircraft was not detected by the controller and why the automated warning systems failed to alert the APP/ARR Prague controller to the presence of the Cessna 172.
Investigators found that the air traffic controller did not identify the unauthorized traffic due to poor target resolution on the E2000 radar display, noting the target appeared as dark blue against a gray background. Furthermore, the investigation revealed significant flaws in the implementation of the