New Europe-wide air traffic control system

Late last year, when the Maastricht Upper Area Control Centre in the Netherlands switched over to a new flight data processing system, it marked the start of a revolution in air traffic control. The first in a pan-European network of air traffic control (ATC) systems designed to cut flying times and boost air traffic capacity, and cut airliners' fuel emissions and costs, it heralds a fundamental and long-overdue change in the way European air traffic is managed.

At the moment, division of airspace follows national boundaries controlled by national governments and their own air-navigation service provider (ANSP). Crossing from one airspace to another therefore entails being handed over to successive ATC systems, forcing aircraft to make repeated changes to communications channels and sometimes to heading and altitude.

This, together with the need to follow air lanes marked out by ground-based radar beacons, creates zigzag flight paths, leading to longer flight times and frequent bottlenecks, and hence higher emissions and costs. National airspace also has large areas reserved for military use - areas that may not always be needed - making the use of airspace inefficient.

The current ten million flights a year over Europe stretches the whole system to bursting point and, with air traffic predicted to double by 2030, there's a clear need for a major boost in capacity and efficiency. So the new Maastricht flight data processing system has been designed to meet this need, in accordance with the EU's emerging Single European Sky (SES) regulations.

The SES is doing away with the concept of national airspace and replacing it with Functional Airspace Blocks (FABs), which are based more closely on desired flight patterns regardless of state borders, allowing routes to be more direct. Maastricht has been controlling traffic over Belgium, the Netherlands, Luxembourg and north west Germany for more than 35 years; with its partners in the Benelux states and Germany, it is now joining the French and Swiss in what is to become the FAB Europe Central. Other FABs include the Baltic, UK-Ireland and Portugal-Spain.

SESAR and SJU in control

The specification and development of the future air-traffic management (ATM) technology infrastructure - of which Maastricht will eventually be a part - comes under the auspices of the €30bn SES ATM Research (SESAR) programme. This is managed by the SESAR Joint Undertaking (SJU), a public-private partnership between the European Commission, European air safety organisation Eurocontrol, ANSPs such as the UK's NATS and Germany's DFS, and aerospace companies including Airbus and Thales.

When everything is up and running, by about 2020, Europe will have an integrated ATM system comparable to a company's enterprise network. Airports, ATC centres and so on will act as nodes in the network, and data about flights, traffic density and weather will be shared by everyone using the network.

Key to the new Maastricht system is the move away from the route-based concept to one of trajectory-based control. Here, every flight is uniquely and accurately defined in four dimensions - latitude, longitude, altitude and time - and this definition is used throughout the ATM network. And, instead of placing a flight into an air lane, an air traffic controller - in coordination with the airline operator - can select the most efficient path to fly on a particular day.

This 4D path is called the Reference Business Trajectory (RBT). It's the optimum path for a flight and is calculated automatically in real time using position information from sources such as radar, information from the traffic controller such as heading and flight level, and the aircraft's flight plan. The trajectory is 'requested' by each flight, then cleared and transmitted back to the aircraft by the ATM system. This cleared RBT can be sent back with modifications if necessary, and en-route speed varied to avoid traffic conflicts and to coordinate required times of arrival at key points such as the destination runway.

So the RBT is not necessarily set in stone; rather, it is progressively authorised, either as a clearance by the ANSP or as a function of the aircrew or on-board systems. The crew can also make some changes to the trajectory during flight if, for example, there is a blocked runway or capacity shortfall, through an iterative process called Collaborative Decision Making. This is already used at some European airports but SESAR will spread it across the whole network.

Continuous descent approaches

During flight, new methods of airborne spacing will also come into play to supplement existing methods. These will be applied either by the relevant ATC centre, using the 4D trajectory data, or by delegating it to the pilot.

Another common - although not that new - feature that will be possible with 4D trajectory management will be Continuous Descent Approaches. Here, instead of a flight descending to an airport by stepping down through different flight levels then flying level until it picks up the airport's Instrument Landing System, it stays higher for longer, and then descends smoothly on minimal power until it picks up the landing signal. This cuts noise at ground level and, according to SJU estimates, will on average save each flight 500kg - and as much as 1,500kg - of CO₂.

Getting the different parts of the system to work together to achieve its aims will take technology in three main areas: precision navigation and tracking; automation support; and, network operations. Much of it is either available now or on the horizon, and the latest Airbus and Boeing airliners already have the necessary avionics.

Existing GPS and radar systems will continue to play their part in navigation and tracking, but they will be augmented by a technique called Automatic Dependent Surveillance-Broadcast (ADS-B). This allows aircraft to determine their position using the European Space Agency's Galileo, and later Iris, satellite systems and broadcast it to other suitable equipped aircraft and ground stations.

It is a lot more accurate - by a factor of about ten - than radar, and updates most of its data every second or so, meaning aircraft can safely fly closer together, making better use of airspace. It will also do away with the need for air lanes marked out by ground-based radar beacons, allowing the new, more direct routes. Other data link technologies, such as 1090 ES, Universal Access Transceiver 978MHz UAT and VDL Mode 2 provide comms links to enable aircraft parameters to be transmitted to ATC units and hence increase the accuracy of ground systems.

Human controllers

According to Eurocontrol, however, one of the main constraints on airspace capacity is controller/pilot workload, so many routing control functions will be automated but still keeping human operators as final decision-makers.

The safety body says these routine tasks - such as handling repetitive frequency changes between ATC systems and providing flight-level clearances - typically take up about half of a controller's time. These instructions are currently exchanged with flight crews using voice-based systems but under Eurocontrol's Link2000+ programme they are being migrated to a data-link message exchange system similar to email. Called Controller-Pilot Data Link Communications (CDPLC), it's currently a supplemental method of comms but in the 2020 timeframe is expected to become the primary means.

So far, only the new Maastricht centre is using this technology, and has done so since 2002, connecting to networks from airline IT companies SITA and ARINC that exchange CDPLC instructions over a VDL Mode 2 infrastructure. The SES initiative mandates that all EU ANSPs are CDPLC-equipped by early 2013 and that all new aircraft should be equipped by 2011; older aircraft should have it retrofitted by 2015. So far, about 400 aircraft have adopted the SITA system and more than 2,300 aircraft are using the ARINC system.

On the ground, the Maastricht system will cut controller workload by automating their routine monitoring and conflict detection tasks using a tool called Medium-Term Conflict Detection (MTCD). Although it won't be in operation at Maastricht until the end of this year, MTCD determines whether two aircraft are on conflicting paths from their trajectories, which it calculates first from their flight plans and performance parameters, then refines by continuously monitoring their progress.

It's actually an integrated system of predictive tools provided at Maastricht by Spanish company Indra, that gives potential conflict information up to 20 minutes ahead, allowing controllers to move from a reactive stance to the more proactive role of planning the overall flow of traffic.

In terms of networking, the ATM infrastructure will be connected using what SESAR calls the System-Wide Information Management (SWIM) system, an 'ATM intranet' that will enable everyone from flights crews to airports to share information and allow the Collaborative Decision Making mentioned above. Much of the final detail regarding the technology, procedures and protocols for this, however, is still some way off.

Also still on the horizon are decisions on issues such as what to use as a back-up for GPS and navigation satellites in the event of system failures caused by, for example, solar flares, and addressing Europe's chronic shortage of airport space.

For GPS back-up, the Long-Range Aid to Navigation (LORAN) system of low-frequency radio transmitters has been touted as one possible solution, but its use has been in steep decline for some years - ironically because of the take-up of GPS - and in the US, President Obama is looking to cut its funding entirely. There are moves now to rejuvenate the technology but it will take time and a new political will.

And, while the EU's new ATM network promises to triple en-route capacity, it will mean nothing without a corresponding increase in airport capacity. Eurocontrol itself has said that some capacity targets can only be met through "supplemental actions such as additional runways", but news reports have shown how badly that goes down with nearby residents.

The US and nextgen

It's clear though that a wholesale revamp of Europe's ATM network is essential, and is well under way. This is in stark contrast to the parallel effort in the US, NextGen, which is being set up by the Federal Aviation Administration (FAA).

NextGen is intended to interoperate with the EU's network and share much of the same technology, such as ADS-B and SWIM. In fact, SESAR's work is being developed in liaison with NextGen.

But despite this, and the fact that the current US system now handles about 18 million flights a year - of which 25 per cent were delayed or cancelled in 2008, costing businesses and passengers some $40bn - and is expected to have to deal with nearly 30 million flights a year by 2025, NextGen has been plagued by delays.

The problem, as ever, has been one of funding - the new system is expected to cost $20bn. It hasn't helped that the way the Air Traffic Organization - which will be in charge of NextGen's implementation - is itself organised has been called into question, or that Congress can't even agree on how to fund the FAA. Nor did it win any votes in the US airline industry earlier this year when the Obama administration announced federal stimulus packages to improve infrastructure and help economic recovery, and completely ignored NextGen.

Admittedly the FAA had no one at the helm at the time, but that changed in May when Obama appointed a new administrator, and funding for NextGen is at last set to grow appreciably - up from about $200m for 2008 to about $680m for 2009, with the FAA asking for $800m for 2010.

Yet the American 'can-do' attitude has prevailed, and the momentum behind NextGen has been gathering. In March the FAA announced it was starting to phase in the use of ADS-B, deploying it first in the Gulf of Mexico, where it has never had radar coverage. And on the ground, and unlike Europe, it has started building new runways at several large airports - the new runway at Washington's Dulles International, for example, can handle an extra 100,000 flights a year.

NextGen's development and deployment is on a similar timeline to the EU's ATM network, but these should only be the start. Eventually, this is the way air traffic control will be done the world over.