Although recent events may have moved airport congestion off center stage as a major national issue, delays remain a pervasive problem, in part because of the interdependence of the nation’s airports. The effect of delays can quickly spread beyond those airports where delays tend to occur most often, such as New York La Guardia, Chicago O’Hare, Newark International, and Atlanta Hartsfield. Delays at these airports can quickly create a “ripple” effect of delays that affects many airports across the country. For example, flights scheduled to take off from these airports may find themselves being held at the departing airport due to weather or limited airspace. Similarly, an aircraft late in leaving the airport where delays are occurring may be late in arriving at its destination, thus delaying the departure time for the aircraft’s next flight. Delays have many causes, but weather is the most prevalent. Figures compiled by FAA indicate that weather causes about 70 percent of the delays each year. Apart from weather, the next main cause is lack of capacity—that is, the inability of the national airspace system to handle the amount of traffic seeking to use it. Capacity can be measured in a variety of ways. For example, at individual airports, one measure is the maximum number of takeoffs and landings that can be conducted in a given period, such as 15 minutes or 1 hour. In our 2001 report, we noted that FAA had established such a capacity benchmark at each of the 31 of the nation’s busiest airports. FAA’s data on capacity and demand at these airports showed that even in optimum weather conditions, 16 airports had at least three 15-minute periods each day when demand exceeded capacity. Weather and capacity problems are often linked, because bad weather can further erode capacity. For example, some airports have parallel runways that are too close together for simultaneous operations in bad weather. When weather worsens, only one of the two runways can be used at any given time, thereby reducing the number of aircraft that can take off and land. FAA’s data in 2001 showed that in bad weather, 22 of the 31 airports had at least three 15-minute periods when demand exceeded capacity. Another measure of capacity, apart from the capacity of individual airports, is the number of aircraft that can be in a given sector of the airspace. For safe operations, aircraft must maintain certain distances from each other and remain within authorized airspace. If too many aircraft are trying to use the same airspace, some must wait, either on the ground or en route. Addressing flight delay problems also requires action by multiple aviation stakeholders because no single entity has the authority or ability to solve delay-related problems. The federal government, especially through the Federal Aviation Administration (FAA) and its parent agency, the Department of Transportation (DOT), plays a major role by operating the national airspace system, distributing federal funding for airports, and setting operating standards for all aircraft and airports. Airports and airlines are also important decision makers and funding sources. The nation’s airports are primarily owned and operated by local units of government, so that decisions about such steps as expanding airport capacity are primarily local in nature. Airlines’ business decisions have a strong effect on the volume and routing of flights, the type and size of aircraft used, and the degree to which aircraft are upgraded to take advantage of new technology. Several initiatives to reduce flight delays and enhance capacity are ongoing. These initiatives which FAA, the airlines, and the airports are implementing are incorporated into FAA’s major capacity-enhancing effort: the Operation Evolution Plan (OEP). The OEP is a rolling 10-year plan to increase capacity and efficiency of the national airspace system and focuses on airport surface infrastructure, and technological and procedural initiatives at 35 of the busiest airports in the United States. FAA acknowledges, however, that the OEP is not intended as the ultimate solution to congestion and delay problems. Responsibility for the various initiatives is still shared among the various segments of the aviation community. In February 2005, FAA published version 7 of the OEP and organized it into the following four quadrants: Airport Congestion. The Airport Congestion quadrant focuses on capacity enhancements for the airport surface. One of the most effective ways to increase capacity is to build runways; however, it takes an average of 10 years from the time planning begins for a runway until it is commissioned. To help expedite the process for building runways, Congress and FAA streamlined the environmental review phase of the runway process. In addition, according to FAA, over the last six years, seven new runways were opened at Phoenix, Detroit, Denver, Miami, Cleveland, Houston, and Orlando airports which provided those airports with the potential to accommodate about one million more annual operations (take-offs and landings). Seven more runways and one runway extension are included in the OEP and are scheduled to open by the end of 2008. These runways are expected to provide those airports with the potential to accommodate 889,000 more annual operations in the system, as shown in figure 2. In addition to the runways listed in the OEP, nine more projects are in the planning or environmental stages, including one new runway, three airfield reconfigurations, one runway extension, and three new airports in major metropolitan areas. FAA also has additional flight reduction activities that are not included in the OEP. To reduce flight delays at some of the delay- prone airports, such as New York La Guardia and Chicago O’Hare, FAA is exploring administrative and market based options. For example, FAA is considering auctioning off landing and take off rights at New York La Guardia and is currently limiting the number of scheduled arrivals during peak periods at New York La Guardia and Chicago O’Hare. Air Traffic Management Flow Efficiency. This quadrant focuses on new technology and procedures to optimize the flow of traffic and maximize system throughput which may allow better control and utilization of current airspace. Included is the Collaborative Convective Forecast Product which is a graphical forecast of potential convective activity areas (i.e. thunderstorms) for use in the strategic planning and management of air traffic. It is intended to provide advance planning for long haul flights and allows for schedule predictability based on 2-, 4-, and 6-hour forecasts. This tool is most useful during the severe weather avoidance procedures season, which is from March to October. Another program is Collaborative Decision Making, which is a joint government/industry initiative. Collaborative decision making focuses on electronic data exchange; optimized airspace utilization; shared planning and decision-making; and post-analysis reporting. In addition, the Traffic Management Advisor, which is in operation at eight air route traffic control centers, is an automated decision support tool, is intended to provide controllers and traffic management coordinators more information on airport arrival demand and available capacity for making decisions on aircraft spacing. En Route Congestion. Although the flying public is impacted by delays at the airports, many times this occurs in the en route areas as the airways become congested. The tools in this quadrant reduce delays and contribute to time and fuel savings for the vast majority of airspace users. One of the tools currently in use is reduced lateral (side-to-side) separation may provide space for additional routes between current city pairs or allow for new direct routes. Reduced longitudinal (nose-to-tail) separation may provide more opportunities to add flights without incurring delays. For domestic flights, Domestic Reduced Vertical Separation Minimum was implemented in fiscal year 2005 in the contiguous United States and Alaska and adds six additional flight levels between existing flight levels. The User Request Evaluation Tool which was installed at l7 air route traffic control centers and is operational at 13 air route traffic control centers, allows controllers to predict aircraft-to- aircraft and aircraft-to-airspace conflicts, which allows them to construct alternative flight paths. Airspace redesign projects also provide significant capacity improvements. For example, new routes added as part of the High Altitude Redesign increased en route throughput form the Pacific Northwest into the San Francisco Bay and the Los Angeles Basin areas. Terminal Area Congestion. Terminal airspace is a critical component in the efficient use of airport capacity. In instances where volume has increased and the current airspace structure is the limiting factor, redesigning arrival and departure procedures, including the addition of Area Navigation and Required Navigation Performance procedures, will allow more efficient use of constrained terminal airspace. Also, by applying existing technology with new procedures may provide instrument approaches to nearly all runways greater than 5,000 feet and under a wider range of meteorological conditions that are insensitive to airport surface traffic. Area navigation procedures provide flight path guidance from the runway to the en route airspace with minimal instructions given by air traffic controllers. As a result, routine controller/pilot communications are reduced, which frees time to handle other safety-critical flight activities. Other key benefits include more efficient use of airspace, with improved flight profiles, resulting in significant fuel efficiencies to the airlines. Additional solutions for increasing capacity in this arena are Time Based Metering which is used in conjunction with Traffic Management Advisor, became operational at seven air route traffic control centers. By optimizing the flow of aircraft from the en route to the terminal area, Time Based Metering with Traffic Management Advisor may help an airport to efficiently use the full capacity of its runways which increases acceptance rates as well as peak throughput. An air traffic management tool called Integrated Terminal Weather System which provides full color graphic displays of essential weather information to promote the safety, capacity, and efficiency of air traffic control operations was also implemented at Boston Logan, Denver International, and Minneapolis-St. Paul airports in 2004. According to FAA, the plan is to install the production version of Integrated Terminal Weather System at the New York terminal radar control facility in 2006. A number of challenges in reducing flight delays and enhancing capacity remain.