Creating Smarter Skies

A composite picture that shows flight patterns over a three-hour period across the UK. The image is compiled from real radar data taken on 21 June 2013 © NATS

Demand from airlines and advances in technology mean major changes are now being planned to the air traffic control systems used for communications, navigation, surveillance and coordination. Iain Harris, Engineering Director, Services, and David Hawken, Engineering Director, Operations, both of NATS (formerly the National Air Traffic Services), describe some developments that will further improve the safety, resilience and efficiency of air traffic control systems.

TASKS IN HAND

Air traffic control focuses on getting as many aircraft through designated airspace as efficiently and safely as possible. Effective use of technology has an important part to play in making this a success. As air traffic continues to grow, new technologies are being exploited to improve surveillance, navigation and communications functions. The challenge for NATS is to move away from today’s legacy technology, some of which is 30 years old, to new systems without any interruption to service while maintaining or improving the high levels of safety, service and resilience that have been achieved over the last few years.

NATS is working towards a future where all air traffic management providers are fully networked and connected with a single picture of global air traffic. With this capability, it will be possible to plot an aircraft’s entire route from the moment it leaves the airport. This will make flights more direct and efficient while ensuring safe separation and minimising the controllers’ and pilots’ workloads.

The UK’s existing ATC system relies on a network of radar stations and navigation beacons whose locations date back to the Second World War when pilots usually flew in straight lines from beacon to beacon. Two types of radar are used to track aircraft. Primary radar uses the return from a pulse of energy bounced off the aircraft to detect its location. This is used to ensure that controllers are always aware of planes, even if the other type of radar, secondary surveillance radar, loses contact with an onboard transponder. This will also provide information on an aircraft’s identify, height, and, more recently, other data on the aircraft’s intended actions.

NATS has recently deployed new technology in the North Sea which offers a replacement for radars and does not need the expensive turning gear that is needed to rotate traditional radar. Automatic Dependent Surveillance Broadcast (ADS-B), locates an aircraft’s position using a cluster of sensors that detect an aircraft’s transponder. ADS-B receivers can also be based on satellites which will provide big improvements for the North Atlantic and other remote areas where there is limited radar coverage.

While NATS plans to make increasing use of technologies, including satellites, to monitor the location and movement of aircraft, there will always be a need for some form of primary radar. It is particularly important for detecting any aircraft that do not carry transponders and to detect aircraft that might infringe the UK’s controlled airspace. NATS and other providers must also be prepared for rare but high-impact events, for example, if solar storms temporarily knock out satellite systems.

A more strategic approach to ATC will depend on greater collaboration and sharing of flight information. The strategic approach is in contrast to the traditional tactical approach. Rather than deal with conflicts as they arise, the strategic approach is about planning the whole route in advance to avoid conflicts, making longer-term plans for flights, and factoring in all available information. This involves bringing together information from many sources that manage or can affect each flight, including the airlines, airports and weather forecasting agencies.

Accurate weather and wind speed information is essential as it impacts on how aircraft perform and the amount of fuel they use. More cooperation and exchange of data will also be required between the air traffic control organisations involved with each flight, which includes those at the departing and arriving airport as well as the en route air traffic service providers for each country that the aircraft flies through.

The European Commission’s Single European Sky (SES) programme, in which NATS is taking a lead, intends to coordinate the design, management and regulation of airspace across Europe. SES aims to harmonise en route air traffic management (ATM) across Europe so that it becomes a seamless operation and delivers improvement in safety, capacity and cost.

National Air Traffic Services Terminal Control at Swanwick, Hampshire is staffed by 1,300 people. This centre started operating in 2002, when it began handling aircraft flying over England and Wales. The operations room in Swanwick contains the London Area Control Centre, which manages en route traffic in the London Flight Information Region. This includes airspace over England and Wales up to the Scottish border. It also hosts the London Terminal Control Centre, which handles traffic below 24,500 feet flying to or from London’s airports as well as the Military Air Traffic Control which manages services to civil and military aircraft operating outside controlled airspace

Through its Single European Sky ATM Research (SESAR) programme, work is being carried out by NATS and other European air traffic service providers to develop the information systems that will underpin this collaboration. The estimated cost of the development phase of the SESAR Joint Undertaking is over £1.5 billion, shared equally between the European Union, Eurocontrol (the European organisation for the safety of air navigation) and industry. NATS is an associate partner in SESAR along with other ATC operators and systems developers.

JOINED-UP APPROACH

The ultimate vision is of a future in which all ATC providers are fully networked with a single picture of global air traffic. The joined-up approach to ATC depends on the ability to collect and manipulate growing amounts of data on each aircraft’s plans, performance, position and identity. Handling this information inevitably requires complex IT systems. NATS already deploys software tools that use the increasing volumes of information from radar and other sources to improve the service provided by Air Traffic Controllers.

An example is NATS’ Interim Future Area Control Tools Support (iFACTS) system which provides controllers with predicted positions, heights and headings for all aircraft in their sectors for the next 18 minutes. Previously, controllers manually assessed the future paths of the aircraft in their sector. The iFACTS system also provides an electronic replacement for the paper flight strips that controllers traditionally use – see COMMUNICATIONS

Another step forward in the evolution of air traffic communications will be to add a full two-way data link between aircraft and ground. At the moment, most communication between pilots and controllers is by voice. Different sectors use different frequencies, but the airwaves are becoming congested as traffic levels increase. Increasing the data communication between controllers and pilots can reduce some of the pressure on voice communication and provide other benefits. For example, it will allow controllers to see data from the onboard flight computer about where the plane plans to go next as well as where it is now. In turn, pilots will have access to better information from controllers. NATS has deployed technology to allow the automatic clearance of aircraft from the stands at the major London airports, which has resulted in a significant reduction in voice communications for both pilots and controllers.

Before airlines can benefit from the greater use of data communications between aircraft and ATC, they have to invest in expensive onboard technology. While Swanwick and Prestwick have been fully equipped for datalink services since August 2013, there has not yet been a huge take-up by airlines. But with a European deadline approaching for the installation of datalink equipment in planes and with more ground-based infrastructure becoming available, Eurocontrol predicts that by the end of 2015, 75% of planes will be equipped to handle datalink services.

Improving data links between aircraft and ATC will be important in the next stage in strategic flight control. This would extend to planning entire flights in advance, from gate to gate. It would also lessen the chances of a misunderstanding while at the same time freeing up the pilot and controller for other tasks – a two-fold safety advantage. This will require collaboration and communication between airports, flight operators and national ATC providers to agree on a ‘four-dimensional trajectory’ that sets out exactly where the plane will be and when. Flight planning and control must also include up-to-the-minute weather forecasting so that pilots can adhere to their pre-cleared flight paths with minimal adjustments.

iFACTS EXPLAINED

An international team of engineers from NATS and major suppliers including Lockheed Martin and Altran-Praxis developed iFACTS and worked on the validation and training needed to integrate it while continuing to deliver a normal service. The validation process used real-time simulation facilities available at NATS and an analysis of the precision of the weather models provided by the UK Met Office to understand the impact of any inaccuracies.

An air traffic controller in the London Area Control operations room using an iFACTS-enabled radar workstation

The system comprises a number of tools to assist controllers in their decision-making:

- Trajectory prediction calculates where an aircraft will be up to 18 minutes in the future, based on its current level, speed and heading. This is updated if controllers make a tactical change, and instruct a pilot to change course. Flights are monitored by iFACTS to ensure they conform to the clearances issued.

- Medium-term conflict detection (MTCD) uses the output of trajectory prediction to determine the likely future separation of each pair of aircraft in a sector. Using a ‘traffic light’ system of colours for the closeness of separation, the system categorises predicted interactions as head-on, crossing or catching-up.

- Separation monitor displays the output of MTCD visually, plotting the predicted minimum separation distance for each pair of aircraft and the time until it will occur.

- Level assessment display helps the controller issue clearances for changes in aircraft levels. The display shows predicted climb and descent profiles for a selected flight and potential interactions with other aircraft along the route.

- Flight path monitor checks the conformance of an aircraft to its predicted trajectory and issues an alert if there is a significant deviation. iFACTS then generates a new prediction and updates the predicted interactions. Traditionally, controllers had to manually scan their radar displays to spot aircraft that were not following their clearances. Automating this process means the controller can safely manage more flights because some of their workload has shifted to the system.

4D COMING

Airlines already use a limited form of 4D trajectories for routes across the North Atlantic, where there are few radar locations and communications and surveillance are more basic. As a result, planes are required to maintain a greater separation for safety.

Managing and processing the huge amount of information from airports, airlines and air traffic control that will be needed to make 4D trajectories a reality will require new flight- data processing systems. Two European consortia are developing alternative systems. NATS is working with the German and Spanish providers of air traffic control on the iTEC system, designed by Indra, while the ATC providers for Ireland, Sweden, Denmark and Austria are part of the COOPANS consortium with Thales Aerospace.

Large consortia are needed to share the cost of these expensive systems and to develop common concepts for their operation. For example, these iTEC and COOPANS systems, and any others, must be able to talk to each other. To achieve this, common standards are set through the European standards body, the European Organisation for Civil Aviation Equipment (EUROCAE) and the US equivalent, the Radio Technical Commission for Aeronautics (RTCA). Almost every air traffic service provider, regulator and aircraft manufacturer which aviation equipment provider is a member of these organisations which develop the standards needed on a consensus basis and so are by the industry, for the industry.

Ultimately, the 4D trajectory concept will be expanded further than just the time an aircraft is flying through all the time it is in service, factoring in movements of luggage and passengers, refuelling, de-icing and resupplying when on the ground. This will require greater collaboration between airports, ground agents, airlines and ATC providers. This new approach to ATC could offer huge benefits to passengers as well as to airlines. For example, you could receive advance notification of any delays to your flight well ahead of time, rather than having to travel to the airport and wait.

While it can be confidently claimed that new approaches to ATC will reduce fuel use in air transport, it is not easy to quantify these savings and other environmental benefits such as noise reduction. However, NATS needs to make these calculations so that it can report against air navigation flight efficiency targets set by UK CAA to deliver fuel and carbon savings and justify the costs it passes on to airlines.

Recently, as a part of its initiative to improve the fuel efficiency of air travel, engineers and scientists at NATS developed the 3Di airspace efficiency tool. NATS can use 3Di to measure the environmental efficiency of every aircraft under its control and can compare each flight’s trajectory to a ‘perfect’ flight. NATS estimates that more efficient ATC procedures and better use of airspace have saved 800,000 tonnes of carbon dioxide in the UK since 2008. Data from 3Di will also be used by NATS to recommend changes to the way airspace is used to realise further fuel and carbon savings.

Other pressures are also influencing the way in which airlines operate, and their demands on air traffic control. For example, as the EU moves to hold ATC providers such as NATS responsible for weather delays, it becomes even more important for NATS operations to be resilient against poor weather. One way in which NATS can respond is to adjust flight paths to accommodate weather variations. Traditionally, on their descent to an airport, aircraft must be a fixed distance apart, typically three miles. But just as the safe stopping distance for a car reduces at slower speeds, if planes are coming into land more slowly because of headwinds they should be able to operate safely with a smaller separation.

TIME-BASED SEPARATION

In the spring of 2015, London Heathrow will become the world’s first airport to bring in a new system that manages incoming flights by time separation instead of distance. Usually, flights are separated by set distances decided by the type of aircraft and the size of the wake vortex they create as they fly.

At Heathrow a plane takes off or lands every 45 seconds. In strong headwinds, aircraft fly more slowly over the ground, so maintaining a set separation distance reduces the landing rate and can have a significant knock-on effect on airport capacity.

The introduction of a time-based separation at Heathrow will save 80,000 minutes of delay every year – halving the current figure for delays due to headwinds. NATS undertook three years of testing and studied 10,000 flights to measure the behaviour of aircraft wake vortices in strong headwinds. The results showed that they dissipate more quickly in windy conditions, thus allowing aircraft to be closer together on final approach.

FUTURE INITIATIVES

Engineers at NATS have developed tools to separate approaching aircraft by a fixed time rather than a fixed distance. High headwinds are the single greatest cause of delay at UK airports, so both airports and airlines have been keen to see the introduction of this new technology – see RADAR REPLACEMENTS

Over the past decade, NATS has replaced radar equipment that is nearing the end of its life. It is upgrading 23 main stations with more accurate and reliable technology, at a cost of £164 million. Before this upgrade, all radar sites had to be manned to ensure resilience. Now, thanks to newer equipment that is easier to maintain, there are staff at only two sites on remote Scottish islands. Maintenance crews routinely visit other sites just once a year.

The radars had to be brought into service without major impact on air traffic control. The exercise won the Project of the Year at the 2013 Association of Project Management Awards with the comment, "It has been akin to resurfacing the M1 during rush hour without closing any lanes or affecting the traffic!"

NATS radar systems face another engineering challenge in the spread of wind turbines throughout the UK. Turbines interfere with the communication, navigation aids and radar networks. Rotating blades can create a 'sparkle' or clutter on radar displays with false radar images that mimic a plane's wing. They can also mask the location of aircraft in the area, which is why NATS has to be consulted on all wind turbine planning applications.

As a part of its work to accommodate wind turbines, NATS is upgrading two of its radars and their associated infrastructure at a cost of around £12 million. In February, NATS signed a deal with SSE and Vattenfall to modify two Raytheon-manufactured radar sites and to provide a mitigation service in northern England and southern Scotland to the interference caused by wind turbines.

BIOGRAPHIES

Iain Harris is Engineering Director at NATS Services, responsible for the delivery of the engineering services at 20 airports in the UK and providing technology-based solutions to customers in the UK and internationally. He started as an engineering apprentice with NATS 27 years ago and has undertaken senior managerial roles at Stansted and Southampton Airports.

David Hawken is Operations Director, Engineering, at NATS, responsible for leading the team of 800 engineers who design, procure, operate and maintain the engineering systems used to provide en route ATC in the UK. He is a Chartered Engineer, Fellow of the IET and has a degree in Electrical and Electronic Engineering.

The authors would like to thank Martin Griffiths and Michael Kenward for their help writing this article.