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control. As discussed in the introduction, currently flight planning is made globally by its CFMU unit a long time in advance but without achieving optimal flow and under data estimates that are almost certainly incorrect, whereas flight control is made locally by its ATCC units when more precise data is available but without a global view, so that na¨ıve re-planning takes place.

A manifestation of this lack of integration of planning and control is that the delays reported in Table 2 and Figure 2 would seem quite unacceptable (for instance, about 20% of the flights incur at least 30 minutes of delay). This is due to the poor cell demand distribution of the input flight plans (see Table 1) and is thus an argument for the proposed tighter integration of planning and control. Related Work. Our previous project [6] with EuroControl headquarters in Brussels (Belgium) is here extended from five airspace sectors (covering a bit more than the three BeNeLux countries) to the entire ECAC airspace, divided into box-shaped cells rather than the current sectorisation, and (initially) using capacity as a metric rather than some form of air-traffic complexity. Since this is a very large jump in the size of the input data, and since the technique to be developed even has to cope in real time with traffic volumes of the year 2030 (about 50000 flights per day, as opposed to the 20000 flights nowadays), our first idea was to use CBLS instead of the traditional constraint programming (by heuristic-guided global tree search with propagation at every node explored) that we deployed in the previous project. Since the chosen CBLS modelling language, namely *Comet*, also has constraint programming (by global search)
and integer programming back-ends, we plan to keep the model and evaluate the actual necessity of this choice.

The works closest to ours were tested on actual flight data of the year 1995 for all of France [4] and the year 1999 for one French ATCC [2]. In further contrast to our present work (which was tested on projected flight data of the year 2030 for the entire ECAC airspace, divided into uniform cells rather than sectors), traditional constraint programming (rather than CBLS) was used toward satisfying the capacity constraints of all sectors, and the objective of the latter work was to minimise the maximum of all the imposed ground holdings (rather than their sum).

Another important related work concerns the airspace of the USA [8]. The main differences with our