The aim is to introduce Unmanned Air Systems (UAS) into controlled airspace without special segregation arrangements. It is necessary that airlines and their passengers not be exposed to higher risks of mid-air collision. The analysis here sketches processes of policy decision-making and safety analyses that should lead to a reasoned conclusion. Air Traffic Control (ATC) Systems are High Reliability Organisations (HROs), whose characteristics include: focus on safety, effective use of technological improvements, learning from accidents/incidents, and an underpinning safety/learning culture. Accidents are now the product of rare and complex "messes" of multiple failures, and hence it is a continuing challenge to preserve the HRO status. The different ways of safety analysis for UAS introduction are Target Level of Safety (TLS) methods, modelling absolute risk synthetically and comparing with a target derived from current safety performance, and Relative methods, comparing a new system with an existing one. It is very difficult to use TLS for whole-system changes, as there are problems in actually estimating the currently achieved or projected level of safety with precision. Such estimates need many statistical assumptions about a model's failure structures, human factors and managerial failure conditions. The Relative method will work if the new system is sufficiently similar. A proposed specific "Equivalent Level of Safety" is: "An additional Unmanned Air Vehicle (UAV) operation must not increase collision risk to current civilian conventionally piloted aircraft (CCPA) more would than an additional CCPA operating on similar routeings." If ATC handles UAS exactly the same as CCPA, the fundamental need is for UAV to have Airborne Collision Avoidance System (ACAS) Xu equipment, at least as effective as CCPA Traffic Alert and Collision Avoidance Systems (TCAS). ACAS Xu Resolution Advisories (RAs) are linked to the Flight Management System, ie an automatic response. Hazard analysis has then to concentrate on potential CCPA/UAS differences. Two important components are contingency routeing when the UAV/Ground Control Component (GCC) datalink fails (causing eg marked increases in ATC workload), and safety/learning culture of GCC managers/staff. Knowledge of cultural performance is not available a priori: it requires empirical evidence of hazardous incidents and safety processes. Safety analysis must also include stress testing of system resilience by real-time simulation of novel events. If policy makers prefer not to opt for the strong decisions here - on UAV equipage, implementation of ACAS Xu, use of Equivalent Levels of Safety (ELOS), small datalink latencies, safety/learning cultures - then the process of safety analysis to justify UAS non-segregated use of airspace would be markedly more complex.
Introducing unmanned aircraft systems into a high reliability ATC system
The Journal of Navigation ; 66 , 5 ; 719-735
2013
17 Seiten, 5 Bilder, 3 Tabellen, 33 Quellen
Article (Journal)
English
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