Europe's new Central Flow Management Unit promises to make life easier for its embattled air traffic controllers.

Julian Moxon/PARIS

European air traffic increased by 4.8% in 1994, which is around the annual level of growth predicted until at least the end of the century.

Unfortunately for passengers, and for those struggling to make the air-traffic-control (ATC) system more efficient, the number of delays increased by 7.8% during the year. While this is a considerable improvement on earlier years, it shows that the battle to solve the annual nightmare faced by every summer traveler is far from over.

The effort to reduce ATC delays is being led principally by Brussels-based Eurocontrol, which was charged by its member governments in the late 1980s with integrating, and eventually harmonising, the many uncoordinated elements of the European system. The European ATC Harmonisation and Integration Programme continues unabated, and is gradually having its effect - delays in 1994 would have been far worse but for the quiet improvements which have taken place in the last three years.

While ATC is crucial to the safe handling of the thousands of aircraft which occupy European airspace every day, it works only in real time and therefore lacks the predictive qualities needed to avoid the unforeseen peaks in traffic which lead to severe delays.

Recognising this, the USA and Europe have embarked on air-traffic flow-management schemes to ease the flow of aircraft into and out of congested airspace regions. The aim is to combine long-term strategic forecasting with medium-term ("pre-tactical") and short-term ("tactical") planning to understand - and therefore predict - traffic flows throughout the congested, European airspace. When this is used to support the daily ATC effort, the efficiency of the system should be significantly improved.

On 28 April, Eurocontrol hopes to begin the final stage of conversion to its new Central Flow Management Unit (CFMU) based in a new building at Haren, Brussels (which is now also Eurocontrol's headquarters).

While it will not directly increase the capacity of the over-stretched European ATC system, the CFMU (elements of which have been in operation for several years) should drastically ease the pressure on the system during peak times. CFMU chief Dirk Duytschaever is reluctant to go further and claim that there will be significant cuts in delays, but he admits that recent simulations of the system's ability have shown the potential for reductions of "at least" 10% and possibly more.

Last year "...really strained the [ATC] system to such a degree that any small disturbances caused a disproportionate effect", says Duytschaever. While its impact was reduced by the coordinating efforts undertaken by Eurocontrol, the strike by French air traffic controllers achieved just such a result.

"Our task is to manage inequality," says Duytschaever. If the amount of traffic is more than the capacity of the system to handle it, the CFMU should manage it in such a way that the actual flow approaches the capacity designed by the authority concerned.

To date, a declared capacity has often not been met because the authority is reluctant to risk taking more aircraft than it can manage during a particular period. The maximum inequality between airspace demand and supply occurs during the peak morning and afternoon times,

"It's very dynamic," says Duytschaever, "not only because of daily peaks, but because of seasonal variations, human factors and local disturbances such as strikes."


The first two elements of the CFMU - strategic and pre-tactical planning - are already working, and have been proving their worth. The strategic element looks at air-traffic flows as far ahead as six months, on the basis of the route planning being made by airlines, holiday operators and so on. This information, essentially on air-traffic trends, is passed to national authorities to help with ATC predictions for the coming season.

Next to be introduced was the pre-tactical system, which looks at traffic flows up to 48h before the actual flight. This takes account of late changes of schedule by airlines, and of differences which have come about in the local environment, such as the introduction of new ATC radar, or the arrival of new carriers on a route. Repetitive airline-flight-plans may also be introduced. "We expect to achieve a predictive accuracy of well over 90%," says Duytschaever. The system draws on information gathered on previous "similar occasions", such as the day of the week and time of year, bringing in other, more random, factors, such as current and predicted weather, to allow development of an operational flow-management plan.

The pre-tactical system has been in operation since October 1991. At noon every day, the CFMU publishes its daily Air Traffic Flow Management Notification Message (ANM), which is transmitted automatically to airlines, ATC centres, and any other parties equipped with a CFMU terminal. Seventy-four such terminals have already been installed throughout Europe "...and I'm sure there will be a demand for more, once we start full tactical operations", says Duytschaever.

The hoped-for introduction of the final, tactical, flow-management element of the CFMU on 28 April will see the gradual end of the five regional flow-management centres in Frankfurt, London, Madrid, Paris and Rome. It will, for the first time, bring under one roof the entire European flow-management picture, taking into account all of the restrictions, re-routeings, and other problems which can occur on the actual day of the flight.

Tactical flow-management planning is achieved largely by building up a picture from aircraft flight plans of what will happen on any particular day. In the CFMU, the way in which flight plans are distributed throughout the system has been revolutionised. Previously, a flight plan filed by a pilot flying, for example, from London to Budapest, would have to be processed in Brussels, Frankfurt and Vienna.

"They were being processed an average of 2.7 times," says Duytschaever, "which was not only inefficient, but meant that mistakes were sometimes introduced along the way."

The new Integrated Flight Planning System (IFPS) at Haren, and its back-up system at Eurocontrol's Paris centre, will change all that. Now, without fail, every flight plan will pass through the IFPS, be checked for correct syntax, and presentation, be validated, and then distributed automatically to every CFMU terminal in the system. "It will help reduce delays," says Duytschaever, "because air-traffic control and air-traffic management will always be working on the same flight plan."

The demand being placed on the system will thus be known immediately, allowing users to see at a glance where the problems are. "The procedure is that a pilot will file his flight plan 3h in advance of any published restriction," says Duytschaever. "We then guarantee that he will get a slot 2h before departure. If there is a restriction, he gets a slot, with the possibility of a delay. If there is not, he can depart without a slot having to be allocated".

Airlines equipped with a CFMU terminal will be able to plug into the system themselves and see where the bottlenecks are occurring. While it will never on its own solve the problem of under-capacity of the system, it should, once the airlines begin to use the CFMU fully, help redistribute the load to reduce peaks, so that there are fewer bottlenecks. ATC centres will be fed traffic in a more measured way, smoothing what Duytschaever calls the "dynamic inequality" inherent in an overloaded airspace system such as that of Europe. "When it is necessary to introduce penalties," says Duytschaever, "it will be ensured that these are shared as equally as possible by all aircraft operators."

The CFMU, says Duytschaever, "is a recognition of the fact that you cannot do flow management efficiently on a national scale. It is now becoming a global it is common sense that the next phase must be to find an interface with North American flow-management systems."


The operational evaluation for the tactical flow-management system has been running for about a year, with numerous revisions being made to the 700,000 lines of software it contains. A series of rehearsals of a "live" system has been run, which exposed initial problems with the level of acceptance of flight plans in the IFPS. "Improvements in data capture by operators, in the robustness of the CFMU systems, and in their operation, must continue," says Duytschaever.

Introduction of the IFPS is due on 28 April, when the tactical flow-management system is to be switched on. "That's our slot," says Duytschaever, "because, if we miss it, we'll have to delay the switch-on for six months, to avoid upsetting the summer schedules." He says, however, that he is "very optimistic" that operations will begin smoothly in April.

Close-down of the existing five Flight Management Units will begin with Paris in April, followed by Frankfurt in October, then London and Rome and, in summer 1996, Madrid. This time-scale is slightly delayed from the original, which foresaw the retention of IFPS centres in several countries. "We realised this was not necessary," says Duytschaever, "because we could carry the load in the two CFMU centres in Brussels and Paris."

The summer of 1994 provided the first major demonstration of the CFMU's capabilities (albeit lacking the tactical element). Abnormal delays at Majorca's Palma, strikes in Greece and Marseilles and re-routing of traffic around the former Yugoslavia have all been handled without fuss. As the value of the system becomes apparent and, as more airlines obtain their own CFMU terminals, there is little doubt that the extreme burden suffered every summer by Europe's air traffic controllers will be lightened.

Source: Flight International