All under control

Citation

(1998), "All under control", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 1. https://doi.org/10.1108/aeat.1998.12770aab.001

All under control

All under control

Britain's Civil Aviation Authority (CAA) has monitored an overall spell of unprecedented growth in British aviation during its 25-year existence. Today, 25 years after Sir Ronald Edwards' far-reaching survey and report into the UK's aviation industry were implemented to initiate the CAA, the organisation is preparing itself to oversee an even more expansionist future.

CAA's workload across its various responsibilities, including the economic regulation of UK airlines and air travel aviation research and air traffic control, is increasing yearly. Of these, the boom area is in air travel with the 100 million passengers who today pass through UK airports expected to double in numbers by 2010.

CAA's responsibility for coping with ever-busier air movements required to keep this immense quantity of people safely on track is managed by the National Air Traffic Services, NATS. The skills of this 5,000-strong team of air traffic controllers, engineers, scientists and support staff are harnessed to provide safe passage for the 5,000 or more aircraft that fly through the airspace over the UK each day ­ most of them commercial airlines making scheduled or charter flights to and from hundreds of different cities around the world.

In the mid-1980s the rapidly increasing size and complexity of this task and the introduction of vastly more capable new communication technologies led NATS to identify the need for a new air traffic control centre for the late 1990s and beyond. This centre required a new site, new buildings and plant, new electronic systems, new air traffic control procedures and all the necessary logistics to support its effective operation.

Behind the decision to go ahead with this major modernisation was the basic requirement to provide for the "sectorisation" of UK airspace and for route restructuring, together with greatly increased computer assistance and improved capabilities for communications, training and simulation.

The Southampton area on the UK's south coast was identified as the site for NATS' ambitious new facility and in 1991 construction got under way, culminating in the handover of the new Swanwick Centre to the CAA in 1994.

In 1997 the UK government confirmed NATS' future strategy of concentrating its efforts on two air traffic control centres: Swanwick and its counterpart at Prestwick's new Scottish Centre. They will handle respectively the airspace over England up to 55 degrees north (designated the London Flight Information Region, or FIR) and airspace over Scotland, Northern Ireland and surrounding seas. In addition, the UK is responsible for managing traffic in the Oceanic Region covering the busy eastern part of the North Atlantic.

At Swanwick, the centre's airspace is divided into some 30 sectors. The number of aircraft on frequency within a sector is approximately 15 to 20 at any one time, although this figure varies throughout the day and is influenced by the time of year.

Each sector comprises three people ­ a planner and tactical controller with appropriate assistant support ­ and occupies three computerised workstations. Military teams at the centre will comprise three controllers with the planner sitting between the two tactical controllers, and will be able to communicate electronically with civil workstations around the the 2,000 square metre floor of the operations room.

Between them they handle every flight into and out of UK airspace. They receive information about proposed routes and timings from the flight plans that are filed by all aircraft.

When an aircraft arrives in a particular sector of airspace it is the job of the controller concerned to keep it safely separated from other aircraft ­ a task achieved by allocating different altitudes and by arranging minimum horizontal distances between aircraft.

Normally the essential communication between controllers and pilots is maintained by VHF and UHF radio-telephony (RT). A total of 26 transmitter/receiver stations are located around the UK, giving controllers at Swanwick access to more than 130 RT channels.

Transponders fitted to aircraft flying in controlled airspace are interrogated by a ground signal to check information such as the aircraft's altitude, call-sign and destination. This information appears as a label next to the aircraft's position indication on the controllers' screens.

At the Swanwick Centre radar displays are fitted in modern workstations that combine the technical features of high-resolution displays and computers. By linking with external data systems, information such as the prevailing weather at any given airport or the order in which aircraft will arrive and depart can be selected for display by using a menu in the computer's window.

Incoming radar signals are converted into digital form and passed from a chain of radar stations to the control centre along a network of landline links. Like the radio installations, many of these stations are in remote locations and not permanently staffed ­ but the technical performance of each is monitored constantly by System Control at the centre.

Swanwick's operations room, believed to be the largest in the world, is unusual because workstations are aligned in curves rather than the traditional straight lines. This layout allows both oral and electronic communication between members of the same or different sector teams where airspace sectors abut.

The 30 sectors in the chosen layout are grouped in five local areas, each of which has a supervisory position with a direct line of sight to all sectors in that area.

Each three-workstation sector suite is equipped with 70cm 2,000-line colour monitors that can display a wide range of data as well as the radar picture itself. Secondary information is displayed on smaller, adjacent screens. Between them they give controllers access to radar data, electronic flight progress strips, and the means to sort, filter, highlight and display all the data available.

This system combines leading-edge techology and techniques with commercial off-the-shelf products. The sector is served by 23 subsystems and two million lines of computer code.

At the sector, the controller controls aircraft in his area using radar and paper flight strips. Aircraft are transferred to the sector RT frequency by the previous sector. The tactical controller uses information on the paper flight strips, together with the entry and exit conditions specified by the planner, to issue instructions to the aircraft to ensure its safe passage through the sector.

The planner co-ordinates aircraft in and out of a sector using radar and electronic flight strips. An aircraft is offered automatically from the previous sector with a proposed entry level into the sector, at which stage the planner considers the proposed entry level against other aircraft approaching or already in the sector to confirm that the offer is acceptable.

Once accepted, the planner then sets the level at which the aircraft will leave the sector and the aircraft is automatically offered to the next sector in the chain.

The position of each aircraft appears on the Swanwick screens as a diamond-shaped symbol, attached to which is a flag containing the aircraft's call-sign, its UK airfield destination code, ground speed in knots, sector entry level, flight level and agreed sector exit level.

The entire centre is serviced by a system control unit, manned on a 24-hour basis to direct the operation, maintenance and deployment of all services and facilities to cover the needs of the air traffic centre.

Computer-based systems are used for processing flight plans and radar-derived aircraft position information. Besides distributing and displaying data to controllers they also predict potential conflicts between aircraft, alerting controllers to situations as they develop.

Computers also store and retrieve flight plan data and take information from the network of radar stations, choosing the best source for each part of the controlled airspace and matching them to the flight plan data already stored to establish track status for each aircraft in the system and to update the flight plan progress information to controllers.

Information is also exchanged automatically between adjacent control centres in the UK and overseas.

The sheer volume and complexity of Swanwick's computerised workload has, perhaps inevitably, delayed its progress towards full operational deployment. NATS, anxious to resolve software challenges in a way that brings long-term benefits rather than simple short-term fixes, intends Swanwick to become fully operational within the next 12 months.

In the further future, NATS and CAA anticipate the Swanwick centre will undergo at least three major upgrades during its 40-year lifespan to cope with the demands of the fast-developing world of air traffic control. A major change in its short- to medium-term will be the elimination of paper flight information strips to electronic ones.

Swanwick is set to underscore the UK's position as a world leader in air traffic control technology and safety ­ and to help maintain the country's air transport industry's high level of contributions to the UK economy well into the next century.