Before revision:  UAS traffic management (UTM) system for low-altitude airspace is therefore immediately necessary for its safe and high-density use. In this paper, we propose the first formalization of FAA's Concept of Operations for UTM for building and analyzing traffic management protocols and systems.
After revision:  UAS traffic management (UTM) system for low-altitude airspace operations. FAA has conceptualized the requirements on UTM protocols and components in the FAA's Concept of Operations for UTM for building and analyzing traffic management protocols and systems.