Extension of WAM and ADS-B systems for TMA/ACC Sofia

The WAM and ADS-B extension project was launched in 2017 and covers the Western part of the controlled airspace of the Republic of Bulgaria. Its implementation aims to provide full surveillance Mode S Enhanced and ADS-B coverage within the boundaries of TMA Sofia and the Western part of the Flight Information Region (FIR) Sofia. The project is implemented through the extension of the existing Multilateration (MLAT) system MSS-A SOF, using 7 sensors from the MSS-A SOF system and adding to them 22 new sensors located at remote sites in the Western part of the Republic of Bulgaria, as well as surveillance data processors. Thus, WAM/ADS-B West – the system obtained through the implementation of the project, has minimal dependence on the MLAT system – MSS-A SOF, despite the use of common sensors. The WAM/ADS-B West system uses Wide Area Multilateration (WAM) technology, which enables wide area coverage.

With the implementation of a WAM/ADS-B West system based on 29 remote sensors, BULATSA improves its surveillance infrastructure as follows:

• All restrictions in the conditions for applying 3NM horizontal separation in TMA Sofia are abolished;

• All restrictions in the conditions for the application of 5NM horizontal separation in the Western part of FIR Sofia are abolished;

• The surveillance coverage in TMA Sofia and the Western part of FIR Sofia is redundant;

• ADS-B coverage is provided within the borders of FIR Sofia, thus complying to Implementing Regulation (EU) No. 1207/2011.

The need for the implementation of the project is caused by the complex characteristics of the terrain in the Western part of the Republic of Bulgaria, which creates limitations in providing surveillance coverage with the use of radars. The implementation of a WAM/ADS-B West system using WAM and ADS-B technologies overcomes these limitations and achieves redundant surveillance coverage with the following characteristics:

• Mode S Enhanced surveillance coverage from altitude 8500ft for ACC;

• Mode S Enhanced surveillance coverage 1000ft below Minimum Vectoring Altitude (MVA) for TMA Sofia;

• Providing Mode S Enhanced surveillance coverage 30NM beyond the Southern boundary of the controlled airspace. The system provides independent cooperative surveillance (Mode A/C and Mode S Elementary/Enhanced) as well as dependent cooperative surveillance (ADS-B).

The system installation, setup and testing is complete. Successful functional tests have been conducted. At the end of June 2023, the system will be commissioned.