Air traffic demand and distribution fluctuates in long-, medium-, and shortterm perspective. In order to ensure safe and efficient flight operations, air navigation service providers need to ensure that enough capacity is available for airspace users. For this purpose, reliable traffic forecasts are necessary to avoid capacity shortages or excesses and subsequently costs. However, the provision of air navigation services is hampered by several effects, i.e., unpredictable traffic patterns and trends. Despite awareness of such problem, there is not a common definition or metric yet to measure the so-called 'volatility.' The aim of this paper is twofold: to set out an approach addressing volatility measures for different spatial and periodical scopes, and to show the effects of demand fluctuations on the ATM system from a holistic point of view. Keywords ATM • ANSP • Performance • Volatility • Fuzzy cognitive mapping 1 Motivation Due to the growing number of flights and the high cost pressure on airlines, the provision of air navigation services (ANS) has recently drawn increasing attention from both the academic and the policy decision-makers perspectives. A major challenge regarding ANS provision is 'planning under uncertainties' as a result, for example, of a volatile traffic demand in terms of movement numbers and flow patterns, which significantly influence resource planning and allocation. Several factors could cause
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