Airborne Precision Spacing: A Trajectory-Based Aprroach to Improve Terminal Area Operations

Abstract

Airborne Precision Spacing has been developed by the National Aeronautics and Space Administration (NASA) over the past seven years as an attempt to benefit from the capabilities of the flight deck to precisely space their aircraft relative to another aircraft. This development has leveraged decades of work on improving terminal area operations, especially the arrival phase. With APS operations, the air traffic controller instructs the participating aircraft to achieve an assigned interarrival spacing interval at the runway threshold, relative to another aircraft. The flight crew then uses airborne automation to manage the aircraft's speed to achieve the goal. The spacing tool is designed to keep the speed within acceptable operational limits, promote system-wide stability, and meet the assigned goal. This reallocation of tasks with the controller issuing strategic goals and the flight crew managing the tactical achievement of those goals has been shown to be feasible through simulation and flight test. A precision of ±2-3 seconds is generally achievable. Simulations of long strings of arriving traffic show no signs of instabilities or compression waves. Subject pilots have rated the workload to be similar to current-day operations and eye-tracking data substantiate this result. This paper will present a high-level review of research results over the past seven years from a variety of tests and experiments. The results will focus on the precision and accuracy achievable, flow stability and some major sources of uncertainty. The paper also includes a summary of the flight crew's procedures and interface and a brief concept overview. Development of Airborne Spacing ApplicationsThe concept of Airborne Precision Spacing (APS) operations in terminal area arrival flows has evolved from several decades of research into aircraft-managed spacing [1], [2]-[6]. Early research indicated that, by precisely spacing aircraft across the runway threshold, variability in threshold crossing times could be reduced, thereby increasing runway throughput [5]. Further, even a small increase in runway throughput could lead to a significant decrease in landing delays for airports during high-demand conditions [1]. Simulator experiments at NASA established the feasibility of using traffic information displayed on the flight deck to enable airborne-managed spacing [3], [6] from crew workload and acceptability considerations. This phase of research also determined that time-based spacing was superior to distance-based spacing due to the successive speed reductions that are inherent in arrival flows.Recent improvements in airborne display and computing capabilities, the emergence of Automatic Dependant Surveillance -Broadcast (ADS-B) technology for the sharing of traffic data, and the growing need for capacity-increasing concepts of operation have sparked renewed interest in airborne precision spacing operations. Starting in 1999, NASA researchers developed a preliminary concept of operations for terminal-area precision spacing operations [7]...

Prototype flight management capabilities to explore temporal RNP concepts

“…It also enables aircraft to execute fuel-efficient descents while following a lead aircraft with different performance characteristics. The NASA Airborne Spacing for Terminal Arrivals (ASTAR) algorithm [16] has been incorporated within the 4D-FMS to provide relative spacing capability.…”

A Concept for Robust, High Density Terminal Air Traffic Operations

“…31,32 NASA Langley researchers have developed a system for managing spacing from the flight deck with speed advisories, and have tested this system operationally. 33,34 Erzberger has proposed a system known as Automated Airspace Concept to nearly fully automate en route air traffic operations by automating separation service and conflict avoidance, and has demonstrated this concept for en route operations as well as arrival operations with metering constraints. 35,36 Effective roles for the human controller, traffic manager, pilot, automation systems and decision support will be critical to the mitigation of inherent system uncertainties and the recovery from off-nominal events.…”

A comparative study of interval management control law capabilities

“…Also, since ASTAR inherently knows the expected speed along the trajectory, which is necessary to calculate the ETA, it is able to bound the output speed to keep the commanded speed relatively close to the expected speed. This has helped keep the commanded speeds operationally reasonable and consistent between different aircraft conducting the same operation and leads to stability in long strings of spacing aircraft [12], [16], [17].…”

“…This work has continued through today with the focus of the NASA research being on improving runway throughput resulting from more precise interaircraft spacing [7]- [10]. To support this work, a prototype spacing tool was developed that used expected route information for both the ownship, also called the IM Aircraft, and the leading aircraft, called the Target Aircraft, to predict each aircraft"s estimated time of arrival (ETA) to the runway threshold [11], [12]. Speed adjustments are calculated to make the difference in the ETAs match the controller-assigned goal, the Assigned Spacing Goal.…”