Probabilistic Operational Volumes to Enable Risk-Based Strategic Deconfliction in Upper Class E

Abstract

The FAA, NASA, and industry partners envision a new concept of operations for very high altitude traffic: Upper Class E Traffic Management (ETM). Consistent with the ideas industry offered earlier as Collaborative Traffic Management in the Stratosphere (CTMS), Version 1.0 of the FAA's ETM Concept of Operations [1] includes collaborative strategic deconfliction wherein operators share operational intent with a service supplier who monitors risk and alerts operators when mitigation is needed. The MITRE Corporation’s (MITRE) Center for Advanced Aviation System Development (CAASD) is motivated to consider how operational intent may be expressed given the nature of uncertainty for very high altitude operations: some aircraft are very susceptible to wind, some flight planning is autonomous, and some have missions whose flight paths follow surface activity. Here, we use the operational volume construct central to strategic deconfliction in UAS Traffic Management (UTM), from which the ETM vision was derived. However, rather than relying on a single operational volume, we propose that an operator provide multiple volumes for different levels of confidence about where the aircraft could be at future moments in the planning horizon. These operational volumes may differ significantly from variation around a nominal path. Furthermore, we offer methods by which a service supplier could interpret these probabilistic expressions of intent to estimate the risk of undesirable proximity between vehicles, a proxy for undesirable events such as a mid-air collision or a hazardous wake encounter. We apply these methods to simulated flights of an autonomous unmanned free balloon (UFB) and solar-powered fixed wing aircraft. We show that the accuracy of risk estimates is sufficient to enable deconfliction via risk mitigation. Service supplier alerts would be triggered when risk thresholds are exceeded; those thresholds would vary with target levels of safety for the operations involved, time to the proximity event, and mitigation protocols. We expect this approach to be as safe as, but less intrusive than avoiding all overlap of operational volumes. Continuing research will compare the frequency and magnitude of intervention necessary with other strategic deconfliction methods to achieve the same levels of safety, determine the parameters of the operational volumes, and explore applying this methodology to other new entrant traffic management.