Effective collaboration between planning controller, tactical controller and pilots in handling various uncertainties and hazards is the result of decades of evolutionary development. The forthcoming paradigm shift to Trajectory Based Operations (TBO) requires a similarly effective collaboration between the TBO layer and a tactical layer. Through agent-based modelling and simulation the authors have recently shown that in a pure airborne self-separation environment these two layers together can yield remarkably positive emergent behaviour in managing uncertainties and hazards, as a result of which very high en-route traffic demands can safely be accommodated. The current paper addresses the question if similarly good emergent behaviour is feasible with a ground based TBO design. The key findings are twofold. A negative finding is that ground-based TBO is not providing the remarkably positive emergent behaviours of pure airborne TBO. Though a positive finding is that ground-based TBO has the potential to safely accommodate high en route traffic demands.

For higher density operation in terminal manoeuvring area, Airborne Surveillance
Application System (ASAS) is seen as a promising option in the future air traffic management
(ATM). One idea of recent interest in ASAS application is Interval Management (IM), which is
expected to support energy-saving arrivals, commonly referred as Continuous Descent Approach
(CDA). The questions are how the IM application achieves safety and capacity in the CDA environment,
and how to identify any potential emergent behaviour that should be taken into
account in the operation design. The motivation for this study is the need to properly understand
the nominal and non-nominal behaviour of many aircraft when the ASAS application is applied to
the CDA environment.
For this purpose, this study has conducted a preliminary safety assessment of the ASAS speed
control for multiple trailing aircraft in CDA operation. This article focuses on ASAS surveillance
failure as one of the critical events during flight. Using Stochastically and Dynamically Coloured
Petri Net (SDCPN), ASAS core components and their interactions are modelled. Through Monte
Carlo simulation via the SDCPN models, the impact of the ASAS surveillance failure on the
airborne-based CDA operation is assessed.