# A Performance-Based Airspace Model for Unmanned Aircraft Systems Traffic Management
###### Abstract  
Recent evolutions of the Unmanned Aircraft Systems (UAS) Traffic Management (UTM) concept are driving the introduction of new airspace structures and classifications, which must be suitable for low-altitude airspace and provide the required level of safety and flexibility, particularly in dense urban and suburban areas. Therefore, airspace classifications and structures need to evolve based on appropriate performance metrics, while new models and tools are needed to address UTM operational requirements, with an increasing focus on the coexistence of manned and unmanned Urban Air Mobility (UAM) vehicles and associated Communication, Navigation and Surveillance (CNS) infrastructure. This paper presents a novel airspace model for UTM adopting Performance-Based Operation (PBO) criteria, and specifically addressing urban airspace requirements. In particular, a novel airspace discretisation methodology is introduced, which allows dynamic management of airspace resources based on navigation and surveillance performance. Additionally, an airspace sectorisation methodology is developed balancing the trade-off between communication overhead and computational complexity of trajectory planning and re-planning. Two simulation case studies are conducted: over the skyline and below the skyline in Melbourne central business district, utilising Global Navigation Satellite Systems (GNSS) and Automatic Dependent Surveillance-Broadcast (ADS-B). The results confirm that the proposed airspace sectorisation methodology promotes operational safety and efficiency and enhances the UTM operators' situational awareness under dense traffic conditions introducing a new effective 3D airspace visualisation scheme, which is suitable both for mission planning and pre-tactical UTM operations. Additionally, the proposed performance-based methodology can accommodate the diversity of infrastructure and vehicle performance requirements currently envisaged in the UTM context. This facilitates the adoption of this methodology for low-level airspace integration of UAS (which may differ significantly in terms of their avionics CNS capabilities) and set foundations for future work on tactical online UTM operations. U  
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grown significantly [3]. This initiative was pertinent to urban operations [4; 5; 6] and set foundations for successive research efforts in this field. In 2016, the FAA released Part 107, an addition to Title 14 of the Code of Federal Regulations (14 CFR), allowing routine sUAS operations in the National Airspace System (NAS) [7]. To date, UAS operations have largely been segregated from manned aircraft. In instances where operations spanned controlled airspace, separation from other aircraft has been ensured procedurally through an approval-seeking process with aviation authorities, and visually by the remote pilot in charge. Current regulations allow Visual Line of Sight (VLOS) operations within both segregated and unsegregated airspace (subject to a lengthy risk assessment process). However, large scale VLOS and autonomous Beyond VLOS (BVLOS) operations are not allowed within low altitude airspace. To prevent interference with manned aircraft, sUAS operations are limited to the open space below 400 ft (122 m) above ground level. However, with the rapid growth of civilian UAS use-cases and operations, it is evident that a dedicated infrastructural framework is required as traffic volumes scale up. The UAS Traffic Management (UTM) concept proposed and spearheaded by NASA aims to provide a framework for safely and efficiently managing the demand and complexity of future operations [8]. The UTM framework proposed and demonstrated through various trials intends to support and enhance UAS operations in both VLOS and BVLOS modalities [9; 10]. The UTM project is structured into four distinct phases or Technical Capability Levels (TCL).