For some years, the European Commission and Eurocontrol have been developing a major initiative to prevent the severe congestion of European airspace that could occur in the near future. Issues include:

• how to handle the growth in air traffic within the next 20 years;
• what concepts to implement;
• what operational changes to choose, and what consequences that would have on existing systems.

The various changes which could be imagined today do not all have the same level of performance in terms of their impact on airspace capacity, flight efficiency, safety, etc. Each change must be evaluated in terms of its benefits, costs and social impacts.