# A Performance-Based Airspace Model for Unmanned Aircraft Systems Traffic Management
## 2 UTM Airspace Design and Operational Concepts
### Urban UAM/UAS Operational Concept  
For On-demand Passenger Air Transportation (OPAT), [PERSON] et al. [32] present a CONOPS that is conceptually similar to current aviation practice, with the pilot taking on the responsibilities of pre-takeoff checks, communication with ATC and post-landing checks. This type of CONOPS is currently gaining traction and industry interest [33]. This forms the foundation on which more advanced concepts such as \"Revolutionary Vehicle Autonomy\" (RVA) and \"Evolutionary Vehicle Autonomy\" (EVA) are based [32]. Two representative operational cases are described in this section: flight over skyline (UAM air-taxi operations) and flight below skyline (UAS delivery operations). These two cases are also addressed in the verification studies presented in Section 4. For UAM traffic, it is recommended to adapt helicopter routes by bounded the trajectories as corridors [34]. However, simply adapting current helicopter routes will not respond to the current demands for Mobility-as-a-Service (MAAS). Hence, in the foreseeable future, it is expected that the user will be able to submit a request by only specifying the intended departure and arrival points. The system will then calculate the most suitable route to accomplish this service. Under these proposed concepts, the flight trajectory will be autonomously calculated and evaluated by its governing UTM system, allowing for minimal human intervention. This is conceptually illustrated in Figure 1. The operation starts when the passenger submits a request for a trip through a UTM service supplier interface. The UTM system with a UTM operator in the loop generates an intended route considering factors such as airspace capacity, traffic management, weather, time efficiency, etc. After the intended routes are confirmed, the passenger boards the UAM platform, and the mission is executed autonomously. The flight can span multiple regions with differing safety objectives and supporting infrastructure e.g., a flight can span the airspace over suburban, urban and airport regions. Emergency scenarios call for the provision of system features that allow human operators to initiate and execute contingency measures leading to a safe and rapid recovery [32].  
For UAS-based delivery operations, the envisaged CONOPs is as follows:  
* Phase 1--the remote pilot submits the intended mission profile to the UTM Service Supplier (USS) and requests clearance to access the intended operational airspace and execute the mission;
* Phase 2--The USS checks for conflict with other operations, and assesses whether the UAS and its corresponding support infrastructure meets the minimum required performance requirements for the intended operational airspace; Upon clearance of these checks, the submitted request is approved;  
Figure 1: Concept of Operations for a conventional “air taxi”.  
* Phase 3--The UAS takes-off and climbs to its cruise altitude;
* Phase 4--When the UAS is enroute to the delivery location, system performance is monitored and potential threats are assessed by both remote pilot and onboard/ground-based autonomous systems;
* Phase 5--Upon arrival at the delivery location, the remote pilot confirms a clearance to land through UTM service, which also triggers a notification to the customer;
* Phase 6--The UAS delivers the package. This can be accomplished in different ways. A cable and tether mechanism is typically employed;
* Phase 7--The customer retrieves the parcel;
* Phase 8--The remote pilot guides the unmanned aircraft back to base, again subject to a conflict check and clearance from the UTM service  
Human operators are required to be in the loop for assuring safety, especially during emergency procedures. However, during nominal conditions, the high level of automation allows the operator(s) to take on a strategic management role, with most low-level (and increasingly high-level) tasks being performed autonomously.