Time-based metering is an efficient air traffic management alternative to the more common practice of distance-based metering (or "miles-in-trail spacing"). The efficiency benefit is most pronounced where air traffic flows merge, such as in terminal airspace, at enroute choke points, overhead merge points, or where severe-weather avoidance routes converge-the primary bottlenecks in today's system. To date, the practice of time-based metering in the United States has been confined to arrival airspace, and only in lessconstrained regions, such as the West and South, in part due to limitations in the national airspace system infrastructure. Thus, time-based metering has not been available to redress the most critical bottlenecks in the national airspace system and, coincidently, those where time-based metering would be most advantageous. This paper discusses a prototype time-based metering system designed to overcome limitations of the national airspace system to produce a more versatile and scalable timebased metering capability. Results of a live, operational field test are presented which validate that the prototype-the Multi-center Traffic Management Advisor-can extend time-based metering operations beyond the terminal area to improve traffic flow at critical bottlenecks en route and on departure. In the field test, which focused specifically on Philadelphia-bound traffic in four Air Route Traffic Control Centers, airborne delay and airborne holding were significantly less when Multi-center Traffic Management Advisor was in use relative to control periods. The results demonstrate that the Multi-center Traffic Management Advisor is effective in coordinating time-based metering programs among adjacent air traffic control facilities, even in the complex Northeast corridor of the United States. This is a necessary step toward addressing the most critical air traffic bottlenecks in the national airspace system. Potential for nationwide time-based metering and its implications for the next-generation air transportation system also are discussed.

A recently developed decision support tool provides a common information space to share information directly across numerous air traffic control facilities. This tool is unusual in that its displays can be used as boundary objects, which are entities in which decontextualized information is presented in the same form to all participants in the collaboration. Through an analysis of the results of 2 years of field tests, this article discusses the benefits of this arrangement, particularly in comparison to alternative concepts for collaborative work displays, and identifies key aspects for the design of boundary object displays.

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The northeast U.S. is arguably the most congested airspace in the world. Four major New York airports have very high total operations counts and are concentrated geographically. Improvements are needed for flow managers' decision support systems, to support proactive intervention leading to smoother arrival flows. A CAASD team addressed this issue by investigating predictive "indicators", i.e., quantifications that foretell a future situation with respect to the balance of air traffic demand and capacity at airspace resources. Most flights in the northeast last less than 70 minutes, so predictions of airspace congestion at least one hour ahead would be most useful, since flow control could therefore extend to pre-departure. Predictions are needed especially during visual meteorological conditions, when congestion is not necessarily an expected outcome. Our approach was to examine historical data, in search of identifiable air traffic management problem situations. These situations were then played-back using an integrated real-time model, combining two previously built CAASD systems (the Self-Managed Arrival Resequencing Tool [SMART] and the Collaborative Routing Coordination Tool [CRCT]. The simulation clock was halted one hour prior to the known situation (congested or not), and predictive indicators were evaluated. This paper documents the successful discovery of a congestion prediction indicator.