Air travel in Europe continues to grow at a rapid rate. For example, a real annual growth of 7.1 per cent was recorded in the period 1985-1990, greatly exceeding a prediction of 2.4 per cent annual growth (EUROCONTROL, 1987). In 2005, the growth of controlled air traffic over Europe was 3.9 per cent and further examination reveals that growth in Eastern and Central Europe exceeded this figure (EUROCONTROL, 2006a). Unfortunately, this growth has not been matched by availability of capacity. Europe suffers from both runway and en-route airspace capacity limitations (Arthur D. Little Limited, 2000). The latter is heavily dependent on controller workload, i.e. the physical and mental work that controllers must undertake to safely conduct air traffic under their jurisdiction through en-route airspace (Majumdar and Ochieng, 2002). In 2006, EUROCONTROL’s long-term forecast (EUROCONTROL, 2006b) gives an indication of the forecast traffic to be expected over Europe by 2025. The forecast considers four main scenarios, as shown in Table 3.1.