再Air-traffic control, September 6th 2014 TQP19 (航空管制)
Flight safety：As more aircraft take to the sky, new technology will allow pilots to pick their own direct routes but still avoid one another In a windowless industrial building on the outskirts of Madrid a group of people are watching a series of coloured symbols move steadily across a bank of computer screens. Each icon represents an aircraft flying over southern Europe. In an adjacent room another group are monitoring flights over part of Asia, and next door all eyes on South America. These flights are not “live” but are simulated by Indra, a Spanish technology company, to train controllers in the operation of a new generation of airtraffic-management systems that promises to make flying more efficient by shortening flight times and reducing delays. What is different about these virtual flights is that some are “free-routing”, which means pilots have the freedom to set their own courses instead of following one another along established flight corridors, as they presently do. Free-routing allows an aircraft to fly more directly to its destination, which for European journeys alone would knock ten minutes off average flight times, thus saving fuel and reducing carbon-dioxide emissions. On the face of it, free-routing seems like a disaster in the making. If fast-moving jets can fly where they want the risk of collision would appear to rise. Yet the controllers in Madrid are relaxed and, apart from issuing a few course corrections to avoid a spot of bad weather, leave the aircraft to get on with it. This is made possible because the trajectory of each plane has been worked out by computers some 25 minutes in advance and the pilots have already been informed of any adjustments needed to prevent a potential conflict. Provided each aircraft sticks its flight plan, there is no need for the controllers to intervene. Traditionally, air-traffic controllers have played a more proactive role in keeping aircraft apart. The corridors which jets fly along function much like lanes on a motorway. They pass through sectors and each sector is monitored by air-traffic controllers with the assistance of radar. When an aircraft is about to enter a new sector, the pilot and controller communicate by radio. The controller then gives the pilot instructions to maintain a safe separation, both vertically and horizontally, from other aircraft. It is a tried and trusted method, but one that will struggle to cope with future demand for air travel. This will be huge. In the past 40 years the number of airline passengers worldwide has grown tenfold to some 3.1 billion in 2013. By 2030 it is expected to reach 6.4 billion. Flight corridors frequently follow historic routes are zigzag around. Many of the routes which cross America are based on where hilltop beacons were lit to guide Charles Lindbergh's mail flights in the 1920s. Plenty of radar systems still resemble 1940s technology and provide only a limited “view” of what is in the air. And in Europe, flights have to negotiate a labyrinth of 64 air-traffic-control areas operated by different national authorities. All this adds to journey times and puts constrains on the system because of the need to maintain the safe separation of planes. A much-needed revamp is underway. Although suffering from delays and budget constraints, America's NextGen air-traffic-modernisation programme is slowly taking shape. European Sky initiative, which is supposed to increase co-operation between a reduced number of control centers. Japan also has a project in hand to renovate its air-traffic-control systems. One element of this moderisation involves fitting new kit to aircraft. This is a system called Automatic Dependent Surveillance-Broadcast (ADS-B). It will be compulsory for jets in Europe by 2017 and in America by 2020. ADS-B uses satellite navigation for pilots to determine their position and is generally more accurate than radar and radio-navigtaion aids. This allows aircraft to be safely spaced closer together, which permits more planes to be in the air at the same time. Crucially, though, it also establishes a data link to control centers and to other planes by regularly broadcasting an aircraft's identification sign, its position and other information. These data, when combined with the known trajectory of the aircraft, mean flight-management can now be “based on where we know the aircraft will be at any particular time,”says Gonzalo Gavin, the director of a programme at Indra to install such a system at a control center in Prestwick, Scotland, run by NATS, a British company. The Prestwick center provides enroute service across northern Britain and for flights crossing part of the busy North Atlantic. Known as iTEC (for interoperability Through European Collaboration), the trajectory-based system was developed by Indra with air-traffic providers in Spain, Germany, Britain and the Netherlands as part of the Single European Sky initiative. In a typical flight, a pilot may climb, descend, change course at various points and speed up or slow down numerous times. But with trajectly-based management, the flight should be smoother and shorter, says Mr Gavin. And it is more likely to arrive on time. The ability to predict the arrival time more accurately should mean less circling in holding patterns while plains wait to land, says Alastair Muir, operations director at Prestwick. That would allow more aircraft to use what is called a “continuous decent approach” when coming in to land. This is a procedure which involves a longer decent, more like a steady glide towards the runway. It requires less engine thrust than having to level out at various stages of the approach, so it saves fuel and is also quieter. A wholesale switch to free-routing will not take place overnight - the aviation industry is notoriously cautious in introducing new technologies and procedures. At first pilots are likely to pick from a number of available routes before free-routing completely takes off. It should enhance safety with an early alarm should something go wrong. Although no one knows what happened to Malaysian Airlines flight MH370, which disappeared in March. The new systems would have alerted controllers that the aircraft was not keeping to its trajectory soon after it changed course.
