Due to their overwhelming success with multilateration in Ostrava, ANS officials launched a program to install a much larger multilateration surveillance network around Prague’s Ruzyne Airport. The system needed to provide the full-time surveillance redundancy required by Eurocontrol for major airports. While Prague’s terminal airspace was already served by two SSRs, the new requirement called for continuous operation of two surveillance systems at all times, which meant that three surveillance sources had to be constantly available if any one of them experienced failure or required maintenance.

Besides meeting the Eurocontrol mandate, the new system needed to fulfill three key objectives for the ANS as well. These were, first, to assure that the necessary high accuracy and probability of detection would support the monitoring of approaches on the airport’s planned parallel runways. Second, it needed to provide the precision, resolution and low altitude detection of all aircraft in the terminal area. Third, it had to provide flight operating services throughout the FIR, with a required overlap of at least 30 NM with neighboring countries’ FIRs.

After extensive feasibility and cost studies, multilateration was the clear choice and installation of the wide area configuration commenced. The MLAT system included 10 receiver stations, interrogators and test transponders, and its surveillance data was fully integrated into Eurocontrol’s ARTAS. Technical testing showed that the originally specified system range of 80 NM was substantially exceeded, with 98 - 99% probability of detection as far away as 120 NM and demonstrated significant improvement in accuracy and target resolution over the present SSR serving the Prague FIR.

As well, the new system had another advantage. While the two conventional radars were operating, the multilateration receiver stations would continue to monitor all traffic in its passive, i.e., non-interrogating, surveillance mode. In this set-up, the system would provide an independent, non-radar check of radar performance. However, should its monitoring of the two radars indicate an incipient or actual failure of either, it would immediately commence active interrogation to assure a seamless changeover.

Do controllers see any difference on their screens when multilateration switches on? No, according to ANS surveillance manager Ivan Uhlir. “There is no difference,” he states, “between multilateration and radar from an operational perspective. The controllers have exactly the same picture.”

By taking this step and supplanting radar with wide area multilateration to meet Eurocontrol’s new terminal area requirement, the ANS established yet another world first in air traffic management.


Prague-Ruzyne International Airport

The Czech ANS first deployed a surface multilateration system and later extended the coverage for wide area surveillance.