Enabling unrestricted UAS airspace access: Performance based navigation

The goal of the integration of Unmanned Aircraft Systems (UAS) in the National Airspace System (NAS) is to achieve “file-and-fly” access to all classes of airspace. This means the UAS will fly without limitations or waivers in airspace shared with other manned and unmanned aircraft. In the case of large UAS operating in a similar manner to transport category aircraft in terminal, en-route and oceanic/remote environments, this includes the ability to perform area navigation. This paper explores the unique challenges of applying the concepts and requirements of Performance Based Navigation (PBN) to UAS. Some challenges include GNSS only navigation, Flight Management System (FMS) capable of flying ARINC 424 path terminators, PBN procedures tailored to UAS performance characteristics, and the ability of the UAS to perform instrument procedures during loss of link. Among these challenges includes the assumption that most UAS will be using GNSS only navigation. This is limiting because if GPS is unavailable, the UAS may be able to coast on inertial navigation for some time but then will be incapable of performing PBN. Also, while ARINC 424 path terminators are not necessarily required to perform PBN, procedure designers create routes and RNAV/RNP approaches under the assumption that operators have a capable FMS. A minimum set of path terminators must be defined in order to perform these procedures in the airspace environment of intended flight. In the case of lost link, careful consideration must be taken as to which path terminators will be housed within the ground station and/or onboard the aircraft to ensure that safety and ability to perform PBN is maintained.