In 2000, an unprecedented number of delays and cancellations in commercial airline flights occurred. At 31 of the nation’s busiest airports, 28 percent of the domestic flights arrived late. Certain flights were almost always late; for example, in December 2000, 146 regularly scheduled flights were late 80 percent or more of the time. The percentage of delayed flights declined to 24 percent in the first 6 months of 2001. According to FAA and others, the decline likely reflected various factors, such as better weather, fewer flying passengers because of the economic slowdown, a strike that idled one carrier’s aircraft for several months, a reduced demand on the system, and actions taken to better manage the nation’s airways. The September 11 terrorist hijacking of four commercial airliners has further contributed to a drop in air passengers and scheduled flights, with major airlines cutting the number of flights by 20 percent or more and one carrier, Midway Airlines, ceasing operations entirely. 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’s La Guardia, Chicago O’Hare, Newark, and Atlanta Hartsfield. Delays at such airports, particularly those with large numbers of flights, can quickly create a “ripple” effect of delays that affect many airports across the country. For example, flights scheduled to take off for such airports may find themselves being held at the departing airport because there is no airspace to accommodate the flight. 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. The September 11 attacks may also have added a new dimension to delays because the more thorough screening of airline passengers at ticket counters and security check points now takes additional time. So far, FAA and airlines have addressed this issue by telling passengers to arrive earlier for their flights and to be prepared for longer processing times. Whether additional security will affect the timeliness of aircraft flights has yet to be determined. 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 air transport system to handle the amount of traffic seeking to use it. Capacity can be measured in a variety of ways. At individual airports, one measure is the maximum number of safe takeoffs and landings that can be conducted in a given period, such as 15 minutes or 1 hour. FAA has established such a capacity benchmark at each of 31 of the nation’s busiest airports. FAA’s data on capacity and demand at these airports show that even in optimum weather conditions, 16 airports have at least three 15-minute periods each day when demand exceeds 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 show that in bad weather, 22 of the 31 airports have at least three 15-minute periods when demand exceeds capacity. Another measure of capacity, apart from the capacity of individual airports, is the number of aircraft that can be in a given portion of commercial 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. FAA’s most recent long-term growth projections, which date from before the September 11 terrorist hijackings, anticipated considerable growth in demand for air travel. FAA projected that the number of passengers served by U.S. airlines would rise by more than 40 percent, to more than 1 billion annually by 2010. What effect, if any, the terrorist hijackings will have on long-term growth still remains to be seen. To accommodate the increased number of passengers it was projecting, FAA expected airlines to increase the size of the total fleet by about 2,600 jets—an increase of about 50 percent. The fastest-growing segment of the fleet is expected to be smaller aircraft called regional jets—that is, jets with 32 to 70 seats but generally with ranges of 1,000 miles or more. As we have pointed out in previous work, the growing use of regional jets in addition to turbojet aircraft currently flying has already added to congestion and delays, according to published studies and experts, but the precise amount has not been determined and likely varies from airport to airport. Besides airlines, other parts of the aviation community are also likely to place increasing demands on the air traffic system. FAA expected increases of about 50 percent in the number of cargo aircraft and the number of smaller general aviation jets, such as corporate jets and jets operated by air taxi or charter services. Some industry analysts have suggested that in the wake of the terrorist hijackings, corporations may make increasing use of such jets, which often use the same airports as those used by airlines. All three groups that are most heavily involved in addressing delay-related problems—federal agencies, airlines, and airports—have important roles. As the agency in charge of the air traffic control system, FAA has the lead role in developing technological and other solutions to airspace issues. FAA and DOT are also an important source of funding. Through the Airport Improvement Program, FAA provided $1.95 billion in grants to airports in fiscal year 2000, and through its Facilities and Equipment appropriation, it pays for such things as improvements to the air traffic control system. FAA and the Office of the Secretary of Transportation (OST) monitor access rights to airports as well as the landing fees that airports can charge. FAA also grants authority for airports to levy passenger facility charges (PFC), which were a source of more than $1.5 billion in revenue for airports in calendar year 2000. Airlines and airports are also important decisionmakers and funding sources. For example, changes in air traffic control technology may require airlines to make substantial investments in new technology for their aircraft. However, the recently enacted $15 billion federal assistance package for the airline industry illustrates the airlines’ dire financial conditions, particularly after the events of September 11. Accordingly, airlines may have a difficult time making investments in air traffic control technology for their aircraft. Similarly, while infrastructure improvements such as new runways often receive federal support, much of the funding is raised at the local level. Government, airlines, and airports have undertaken a wide range of initiatives to address flight delays and increase the capacity of the air transport system. The stakeholders we contacted—DOT and FAA, 8 airlines, and 18 of the most delay-prone airports—identified 158 separate initiatives under way. Earlier this year, FAA issued the Operational Evolution Plan (OEP), which is designed to give more focus to some of the diverse initiatives under way. FAA’s role, in addition to continuing to spearhead the initiatives for which it is directly responsible, is to act as overall coordinator for implementing the OEP. FAA believes that the OEP actions already implemented have contributed to the reduction in flight delays experienced in the first 6 months of 2001. Challenges still lie ahead in other areas, such as introducing new technology, adding new runways, funding billions of dollars of investment, and developing ways to help measure what the efforts are accomplishing. The initiatives cited by DOT and FAA, airlines, and airports include steps for addressing both weather-related and capacity-related delays. Considerable efforts were under way to address weather-related problems, which is the major cause of delays. For example, to deal with the problems arising from thunderstorms and other severe weather in the spring and summer, FAA launched a program called Spring/Summer. Among other things, this program led to daily telephone conference calls between FAA and airline officials to discuss weather and other conditions that might affect the smooth flow of air traffic. The program also led to a new effort to predict severe weather affecting aircraft. Examples of initiatives directly related to capacity included an individual airport’s plans to build new runways, taxiways, or gates; airlines’ efforts to adjust schedules to relieve congestion at some hubs; and FAA’s efforts to seek greater use of Canadian and military airspace. Some initiatives dealt with both weather and capacity. For example, FAA is testing a system that would allow the use of satellite navigation for landing approaches in all types of weather conditions. This system, if successful, will allow airports to operate at higher capacity in bad weather. To an extent, the initiatives begun by each of the three stakeholder groups have different emphases. FAA and DOT initiatives emphasize improving the ability to handle more aircraft in the air, airline initiatives emphasize making adjustments to airline operations, and airport initiatives emphasize increasing the capacity for more takeoffs and landings through more runways and other infrastructure. The initiatives that stakeholders cited are summarized briefly below; appendix II contains a detailed list of the initiatives and their status. DOT and FAA officials identified 29 initiatives under way at their agencies. These initiatives can be grouped into three categories—adding capacity to the system, identifying specific problems contributing to delays, and identifying ways to better manage and coordinate responses to delays. Table 1 provides examples of each category. Some of these initiatives were completed, such as a benchmarking study to provide a better indication of the number of takeoffs and landings that can be supported at 31 of the busiest airports in the national airport system. However, most of the initiatives were ongoing or long-term projects.