Current international regulations and policies do not consider the effect of airborne safety nets in the analysis of safety risks. This widely accepted practice tends to create significant tension between the realization of the ambitious safety improvement targets of SESAR and NextGEN, and standing regulations. In order to close this gap, there is a need for systematic development of safety risk analyses of airborne safety nets within an Air Traffic Management context. The aim of the research described in this paper is to address the systematic validation of an unambiguous mathematical model of Airborne Collision Avoidance System (ACAS) operations, together with its interactions with own and other pilots and with air traffic controllers. The specific modelling formalism used for this is Stochastically and Dynamically Coloured Petri Nets (SDCPN); which supports both mathematical analysis as well as Monte Carlo simulation. In order to build confidence, the focus of this paper is on the performance of a systematic validation of the developed model. This validation includes both comparisons against " real data " and comparison with the results of Eurocontrol's ACAS simulation model. Initial application of this validation process to the novel model shows that it is at least as good as the existing ACAS simulation model. However, the added value is that the novel model defines both an unambiguous mathematical model as well as an unambiguous simulation model.