  The analysis of the dynamics of delays propagation is one of the major topics
inside Air Transport Management research. Delays are generated by the elements
of the system, but their propagation is a global process fostered by
relationships inside the network. If the topology of such propagation process
has been extensively studied in the literature, little attention has been
devoted to the fact that such topology may have a dynamical nature. Here we
differentiate between two phases of the system by applying two causality
metrics, respectively describing the standard phase (i.e. propagation of normal
delays) and a disrupted one (corresponding to abnormal and unexpected delays).
We identify the critical point triggering the change of the topology of the
system, in terms of delays magnitude, using a historical data set of flights
crossing Europe in 2011. We anticipate that the proposed results will open new
doors towards the understanding of the delay propagation dynamics and the
mitigation of extreme events.
