In the spirit of harmonisation across the EUROCONTROL membership, radar and surveillance information is shared across the continent. Jenny Beechener investigates.

A key component of Europe's move to harmonise and integrate its air traffic control system is the sharing of surveillance data between states. By using the radar data collected across the region more efficiently, the system as a whole benefits from more cost-effective operations.

Sharing radar data also keeps to a minimum the electromagnetic pollution arising from surveillance units on the ground. It ensures that the minimum number of radars are installed to achieve coverage throughout the region and keeps down frequency congestion. With these objectives in mind, transport ministers in the core area of Europe embarked on a programme to share surveillance data among the four states of Belgium, the Netherlands, Luxembourg and Germany in the mid-1980s.

The integration project set out to achieve complete homogeneity of service from the air traffic control centres in these states. In practice, this meant they had to create a network by which to distribute the data across borders as well as within national boundaries. Euro-control developed the plan to
implement a Radar Data Network (RADNET) to convey sensor data, processed radar data and monitoring and control data between centres participating in the programme. The network is designed with capacity to handle the data streams from surveillance sources (such as radar) and well as
processors (such as radar data processors) and perform flow control in case of overload.

By 1993 the network included 23 nodes and allowed all four states to share radar data. Steady expansion of the programme has seen installation of 52 nodes, which distribute surveillance data for most of the 38 member states of the European Civil Aviation Conference (ECAC).

The network continues to expand, albeit at a slower rate, as more states - including those bordering the ECAC region - join the programme. In addition to distributing radar data, the programme is being developed to handle new types of surveillance data such as Mode S and Automatic Dependent Surveillance (ADS). Dimitris Doukas is responsible for the programme in the EUROCONTROL surveillance unit. "There is a gradual evolution of the system. There are more applications apart from radar data. We are now making the software capable of accommodating the new requirements that are coming. For example, we need more capacity, and more efficient software structure. By the middle of 2001 we expect to be able to accept ADS and support airport surveillance activities," he says.

The surveillance unit is already working with ADS groups to define what is needed and study the necessary developments to achieve this. Mr Doukas anticipates the software and hardware will be in place to accommodate data from services such as ADS and surface movement guidance and control systems. In the longer term, the network is expected to support communications between ground service operations once the future aeronautical telecommunications network (ATN) is implemented.

In detail, the communication transport medium for the network is a common backbone X.25 packet switching network called Regional ATS Packet Switched Network (RAPNET). In addition to surveillance data, this is also used for the exchange of flight plan data, AFTN/CIDIN messages, and coordination messages such as online data interchange. In order to save backbone line capacity, data is collected in nodes and distributed from these to users. This process relies on the Radar Message Con-version and Distribution Equipment (RMCDE), which allows data to be converted to, and from, different formats.

The development and application of a common format is central to the success of the programme. One of the early challenges for EUROCONTROL was to develop the programme when the standard was still subject to validation and certification. By the early 1990s, there was a fixed, stable common format that was able to support the first applications, but it was not until the end of 1997 that the standard was officially approved. The European standard known as All-purpose Structured EUROCONTROL Radar Information Exchange (ASTERIX) is now accepted internationally, and is included in proposals for common data exchange programmes overseas including the US Federal Aviation Administration (FAA).

EUROCONTROL released an international call for tender in 1988 and a contract to provide a prototype RMCDE was awarded to Comsoft of Germany in 1989. The prototype was accepted in 1990 and EUROCONTROL has an open contract with Comsoft that can be used by member states for the procurement of hardware and software necessary to exchange radar data. Comsoft is responsible for software development, for example the company is adapting the system to accommodate Mode S, and is contracted to provide system support. A team from EUROCONTROL is responsible for installation, integration and maintenance. "We try to keep the same version in every system so that all users have the same software," says Mr Doukas. The software is available free of charge for use on RMCDE systems installed in member states. A central repair facility has been set up at Maastricht for the repair, free of charge, of RMCDE boards.

The common standard has allowed steady expansion of the system by ECAC states. In the UK, a similar network (called CAPSIN) is interconnected With RAPNET to allow data exchange. The French network RENAR is also interconnected with RAPNET to support the exchange of radar data, OLDI and AFTN/CIDIN messages. There are additional RMCDEs now in place in Portugal, Denmark, the Czech Republic, Austria and Slovenia. Further distribution equipment is planned in Switzerland, Slovak Republic and the Hellenic Republic.

Widening the application to include the central European states, a concept similar to RAPNET/RADNET, is planned by states in this region. States participating in the Central European Air Traffic Services (CEATS) project have started to implement a regional data exchange network to distribute radar, OLDI and AFTN/CIDIN messages. This will in turn be connected with RAPNET At the start, the programme set out to provide a more costeffective system of distributing radar data in Europe. By establishing a common standard and working across national boundaries, it has become a cornerstone of the European harmonisation and integration programme. A name change from radar data exchange to surveillance data distribution reflects how the programme has widened its scope to include new types of data such as Mode S and ADS. By establishing a common approach to the exchange of data, you facilitate harmonisation and integration between the different air traffic control systems," explains Mr Doukas. The programme started before the harmonisation programme, and has become one of the key building blocks for the ECAC states."

Jenny Beechener is editor of Jane's Airport Review and a former editor of Air Traffic Management.