An Overview of a Trajectory-Based Solution for En Route and Terminal Area Self-Spacing to Include Parallel Runway Operations

Abstract This paper presents an overview of an algorithm specifically designed to support NASA's Airborne Precision Spacing concept. This airborne self-spacing concept is trajectory-based, allowing for spacing operations prior to the aircraft being on a common path. This implementation provides the ability to manage spacing against two traffic aircraft, with one of these aircraft operating to a parallel dependent runway. Because this algorithm is trajectory-based, it also has the inherent ability to support required-time-of-arrival (RTA) operations. Introduction Concepts for self-spacing of aircraft operating in an airport terminal area have been under development by the National Aeronautics and Space Administration (NASA) since the 1970's (ref. 1). Interest in these concepts have recently been renewed due to a combination of emerging, enabling technology (Automatic Dependent Surveillance Broadcast data link, ADS-B) and the continued growth in air traffic with the everincreasing demand on airport and runway throughput. Terminal area self-spacing has the potential to provide an increase in runway capacity through an increase in the accuracy of over-the-threshold runway crossing times (ref. 2).A follow-on to the terminal area in-trail spacing development (refs. 3 and 4) and the initial development of a concept and implementation for a trajectory-based merging capability (ref. 5) was instantiated in an application called the Airborne Spacing for Terminal Arrival Routes, ASTAR. This concept extended the self-spacing capability beyond the terminal area to a point prior to the top of the en route descent. This implementation was a totally trajectory based concept for the entire arrival spacing operation.A specific implementation of this algorithm to support dependent runway operations, referred to as ASTAR10, provides the ability to manage spacing against two traffic aircraft, with one of these aircraft operating to a parallel runway. This support for parallel dependent runway operations also includes the computation of offset threshold crossing times based on the longitudinal distance offset between the two parallel runways and the ability to use diagonal distance spacing once the aircraft are on parallel approaches (ref. 6). This latest implementation of ASTAR also has a rewritten control law relative to the previous versions that were based on the original Advanced Terminal Area Approach Spacing (ATAAS)algorithm (ref. 3).The overall concept for a trajectory-based solution for en route and terminal area self-spacing is fairly straightforward. If the 4D trajectory of an aircraft and its position are known, then the aircraft's position on its trajectory can be determined. By knowing the aircraft's position on its trajectory, the aircraft’s estimated time-to-go (TTG) to a point, where in the case of ASTAR10 is the runway threshold, is known. To apply this to a self-spacing concept, a TTG is calculated for the traffic to follow aircraft (TTF) and for the ownship, noting that the trajectories do not need to be the same. The nominal spacing time, t