Influences of communication structural complexity on operational safety in regional airspace design

As air traffic management systems have evolved and traffic flows have increased, communications protocols have become more complex. Extra frequencies have been introduced, resulting in different frequencies being assigned to adjacent airspace volumes around airports. Consequently, pilots in close spatial proximity might not be operating on a common frequency. This could fatally inhibit timely exchange of information critical to successful avoidance of a mid-air collision. This paper considers the physical feasibility of communication between aircraft when they operate near radio frequency boundaries. It uses a simple but revealing model of aircraft operation within a multiple radio frequency structure. The model allows comprehensive descriptions of operational and failure modes once parameters such as aircraft velocities, radio frequency structures and communication transmission lengths are specified. The paper uses a novel form of nested plot for high-dimensional data to show how the failure modes are influenced by the parameters. An important conclusion is that circumstances in which problems can arise are not easily predicted during flight. Thus operational experience is not necessarily a good basis for evaluating the safety of communication system design. The model is not intended to be complete or exhaustive; its role is to demonstrate design principles and processes.

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► When flight behaviour and radio operations interact a hybrid system is formed.
► As interaction occurs failure modes can be activated.
► Failure modes can arise without warning, i.e., the system has no design integrity.
► Nested plots for high-dimensional data show the behaviour of the failure modes.
► Operational experience alone is not a good basis of system safety evaluation.