Effects of scheduling and spacing tools on controllers' performance and perceptions of their workload

A human-in-the-loop simulation of an integrated set of time-based automation tools that provided precision scheduling, sequencing and ground-based merging and spacing functions was run in the fall of 2010. These functions were combined into the Terminal Area Precision Scheduling and Spacing (TAPSS) system. TAPSS consists of a scheduler and two suites of advisory tools, one for the Air Route Traffic Control Center (ARTCC, or Center) and one for Terminal Radar Approach Control (TRACON) operations. Both suites are designed to achieve maximum throughput and controllability of traffic. The subject airspace was the terminal area around Los Angeles airport (LAX) and the en route space immediately beyond. Scenario traffic was based on the demand from today's heavy arrival periods, and traffic levels were simulated that matched these or added five, ten or twenty percent to this amount. Eight retired, highly experienced controllers worked two final, three feeder and three en-route positions to deliver traffic to the two outboard arrival runways at LAX (24R and 25L). Although the main research question was whether controllers could safely control the traffic, their level of performance was also of interest and how the advanced tools facilitated or hindered their tasks. The results show that the TAPSS tools enabled higher airport throughput and a larger number of continuous descent operations from cruise to touchdown for the jet aircraft in the scenarios. This contrasts sharply with the “current day” operations in which the Center controllers utilize step-down descents to meter the aircraft. Reported workload levels were lower in the “TAPSS tools” condition than in the “current-day” condition and the TAPSS operations earned cautiously acceptable ratings, indicating the prototype tools have value. The goals of the next generation air transportation system in the United States (NextGen) [1] include maintaining a high level of throughput at airports and improving the efficiency of traffic management in dense terminal areas. The efficient scheduling and control of aircraft from cruise to touchdown during congested periods is a highly complex problem due to many factors including mixed equipage, constrained maneuvering space and inherent system uncertainties [2]. Ongoing research both in the USA (NextGen) [3, 4] and Europe (Single European Sky Air Traffic Management Research) [5, 6] aims to develop trajectory management tools enabling aircraft to execute efficient descents, while simultaneously maintaining throughput that will use (close to) current system capabilities. NASA is investigating a concept for high-density arrival operations [2]. Two of its key elements are i) precision scheduling along routes and ii) merging and spacing control functions. Currently, uncertainty in runway arrival estimation, and therefore also control, limits the utility of air traffic control (ATC) scheduling but the theoretical advantage of a precision scheduling and control system for managing these constrained resources is well understood [2, 7]. An extension to the Center/TRACON Automation System (CTAS) [8] technologies currently under development is the Terminal Area Precision Scheduling and Spacing (TAPSS) system [9], which leverages the increase in prediction accuracy of emerging trajectory management tools such as Area Navigation (RNAV) and trajectory-based operations (TBO). TAPSS is a trajectory-based strategic and tactical planning and control tool capable of trajectory prediction, constraint scheduling and runway balancing, controller advisories and flow visualization. TAPSS enables a simultaneous execution of efficient descent procedures along precision RNAV approach routes as a way to achieve high runway throughput. The sections following in this paper briefly describe the TAPSS, a human-in-the-loop (HITL) simulation to test the prototype system, and some selected results.