Modeling ADS-B Position and Velocity Errors for Airborne Merging and Spacing in Interval Management Application

As a part of the Next Generation Air Transportation System (NextGen), the Federal Aviation Administration (FAA) is developing an advanced airborne Merging and Spacing (M&S) concept utilizing satellite-based surveillance information provided by Automatic Dependent SurveillanceBroadcast (ADS-B). The M&S concept is defined as Airborne SpacingFlight deck Interval Management (ASPA-FIM), which includes both a ground component and an airborne component including a speed control algorithm as a part of the Interval Management (IM) capability. The ground based function establishes a sequence for an IM aircraft conducting ASPA-FIM procedure to merge behind another designated target aircraft at a waypoint with a desired spacing interval, and then maintain the desired spacing interval. The aircraft achieve the spacing requirement through speed commands generated by Interval Management (IM) equipment in the aircraft. The IM speed control algorithm relies upon ADS-B position and velocity measurements broadcasted by the target aircraft, where the position accuracy depends upon the Global Positioning System (GPS) measurement errors including a bias and an instantaneous jitter. Since most mathematical models for GPS position errors do not take into consideration the correlation between the successive position measurement errors, this paper presents a model for time correlation between position measurement errors using a GaussMarkov process. In order to determine the minimum position and velocity accuracy required for successful implementation of ASPA-FIM procedure so that the number of speed commands to achieve the desired spacing is acceptable to flight crew and the errors in the achieved spacing is satisfactory, the paper presents results from a Monte Carlo simulation capability which includes ADS-B position/velocity error models, flight dynamics models, a wind model and an IM speed control algorithm. The paper also describes the determination of a desired spacing interval based on established aircraft separation minima during different phases of flight and estimation of the safety tolerance for operational uncertainties. The simulation results provide a preliminary assessment of minimum position and velocity accuracies required to support this ADS-B application. There is a tradeoff between the number of speed adjustments and the accuracy of achieved spacing interval. Using operational scenarios for en route and descent flight paths into Louisville International airport, example results are presented showing the number of IM-equipment-derived speed commands needed and corresponding spacing interval achieved during merge and maintain phases of flight. A qualitative discussion of expected benefits from the ASPA-FIM application is also included in the paper.