Seung Man Lee

Investigating Effects of Well Clear Definitions on UAS Sense-And-Avoid Operations in Enroute and Transition Airspace

Unmanned aircraft systems (UAS) will be required to equip with sense-and-avoid (SAA) systems in order to fulfill the regulatory requirement to remain “well clear” of other air traffic. This study investigates the effects that different well-clear metrics have on the rate of well-clear violations and evaluates the distribution of distances between aircraft at a wellclear violation in high-altitude enroute airspace. The first analysis determines the predicted rate at which violations of well clear would occur between UAS and manned aircraft operating under instrument flight rules, indicating the frequency with which a sense-andavoid system would create a nuisance alert. This analysis is done both with and without an algorithmic model of air traffic control (ATC) separation provision services. The second analysis determines the relationship between time-based well-clear metrics and the range at which the violation would occur, a relationship that may inform the required SAA surveillance range and the frequency with which violations would occur despite ATC separation standards still being maintained. The analyses are carried out using a fast-time simulation capability of the entire US air traffic system over a single day, including 3000 UAS and more than 50,000 manned aircraft. Results indicate that, without any separation provision, a UAS would encounter a manned aircraft with a range tau (defined as the ratio of the relative range to range rate) of 60 seconds only every six hours. Approximately 75% of such encounters would occur outside the ATC separation standard of 5 nmi.

UAS Well Clear Recovery Against Non-Cooperative Intruders Using Vertical Maneuvers

This paper documents a study that drove the development of a mathematical expression in the detect-and-avoid (DAA) minimum operational performance standards (MOPS) for unmanned aircraft systems (UAS). This equation describes the conditions under which vertical maneuver guidance should be provided during recovery of DAA well clear separation with a non-cooperative VFR aircraft. Although the original hypothesis was that vertical maneuvers for DAA well clear recovery should only be offered when sensor vertical rate errors are small, this paper suggests that UAS climb and descent performance should be considered—in addition to sensor errors for vertical position and vertical rate—when determining whether to offer vertical guidance. A fast-time simulation study involving 108,000 encounters between a UAS and a non-cooperative visual-flight-rules aircraft was conducted. Results are presented showing that, when vertical maneuver guidance for DAA well clear recovery was suppressed, the minimum vertical separation increased by roughly 50 feet (or horizontal separation by 500 to 800 feet). However, the percentage of encounters that had a risk of collision when performing vertical well clear recovery maneuvers was reduced as UAS vertical rate performance increased and sensor vertical rate errors decreased. A class of encounter is identified for which vertical-rate error had a large effect on the efficacy of horizontal maneuvers due to the difficulty of making the correct left/right turn decision: crossing conflict with intruder changing altitude. Overall, these results support logic that would allow vertical maneuvers when UAS vertical performance is sufficient to avoid the intruder, based on the intruder’s estimated vertical position and vertical rate, as well as the vertical rate error of the UAS’ sensor.

A Systems-Based Approach to Functional Decomposition and Allocation for Developing UAS Operational Concepts

In integrating Unmanned Aircraft Systems (UAS) into the National Airspace System, separation assurance is one of the important air traffic services for ensuring safe operations of air traffic. This paper describes an approach to develop a range of operational concepts by describing what functions and technologies are required to maintain safe separation of unmanned aircraft and how those functions are allocated and distributed across primary system elements, such as air traffic controllers, automation systems, aircraft onboard systems, and UAS ground control stations including UAS pilots. A framework proposed in this study identifies key functions and capabilities by decomposing high-level system goals into smaller functions to achieve them hierarchically and also identifies primary system elements to perform the identified functions by decomposing the whole system into smaller systems hierarchically. The framework represents hierarchical functional/physical structure and allocation of functions across system elements at different levels to generate a range of potential separation assurance concepts systematically. The detailed representation of functional decomposition and allocation enables an application of the framework for recommending levels of automation (LOA) developed based on human factors engineering principles. The detailed functional decomposition and allocation framework to develop a concept of operations provides additional analysis capabilities: stability, workflow, and taskload analysis to examine the completeness, correctness, and balance of functional decomposition and allocation schemes for concept development without requiring complex simulations. This paper demonstrates the framework through a case study of providing separation assurance functions for UAS operating in en-route and transition airspace in the Next Generation Air Transportation System (NextGen) timeframe.