FAA is responsible for ensuring safe, orderly, and efficient air travel in and around the United States. NWS supports FAA by providing aviation-related forecasts and warnings at air traffic facilities across the country. Among other support and services, NWS provides four meteorologists at each of FAA’s 21 en route centers to provide on-site aviation weather services. This arrangement is defined and funded under an interagency agreement. In performing its primary mission to ensure safe air travel, FAA reported that air traffic in the national airspace system exceeded 43 million flights and 745 million passengers in 2008. In addition, at any one time, as many as 7,000 aircraft—both civilian and military—could be aloft over the United States. In 2004, FAA’s Air Traffic Organization was formed to, among other responsibilities, improve the provision of air traffic services. More than 34,000 employees within FAA’s Air Traffic Organization support the operations that help move aircraft through the national airspace system. The agency’s ability to fulfill its mission depends on the adequacy and reliability of its air traffic control systems, as well as weather forecasts made available by NWS and automated systems. These resources reside at, or are associated with, several types of facilities: air traffic control towers, terminal radar approach control facilities, air route traffic control centers (en route centers), and the Air Traffic Control System Command Center. The number and functions of these facilities are as follows: 510 air traffic control towers manage and control the airspace within about 5 miles of an airport. They control departures and landings, as well as ground operations on airport taxiways and runways. 163 terminal radar approach control facilities provide air traffic control services for airspace within approximately 40 miles of an airport and generally up to 10,000 feet above the airport, where en route centers’ control begins. Terminal controllers establish and maintain the sequence and separation of aircraft. 21 en route centers control planes over the United States—in transit and during approaches to some airports. Each center handles a different region of airspace. En route centers operate the computer suite that processes radar surveillance and flight planning data, reformats the data for presentation purposes, and sends it to display equipment used by controllers to track aircraft. The centers control the switching of voice communications between aircraft and the center, as well as between the center and other air traffic control facilities. Four of these en route centers also control air traffic over the oceans. The Air Traffic Control System Command Center manages the flow of air traffic within the United States. This facility regulates air traffic when weather, equipment, runway closures, or other conditions place stress on the national airspace system. In these instances, traffic management specialists at the command center take action to modify traffic demands in order to keep traffic within system capacity. See figure 1 for a visual summary of the facilities that control and manage air traffic over the United States. The mission of NWS—an agency within the Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA)—is to provide weather, water, and climate forecasts and warnings for the United States, its territories, and its adjacent waters and oceans to protect life and property and to enhance the national economy. In addition, NWS is the official source of aviation- and marine-related weather forecasts and warnings, as well as warnings about life-threatening weather situations. The coordinated activities of weather facilities throughout the United States allow NWS to deliver a broad spectrum of climate, weather, water, and space weather services in support of its mission. These facilities include 122 weather forecast offices located across the country that provide a wide variety of weather, water, and climate services for their local county warning areas, including advisories, warnings, and forecasts; 9 national prediction centers that provide nationwide computer modeling to all NWS field offices; and 21 center weather service units that are located at FAA en route centers across the nation and provide meteorological support to air traffic controllers. As an official source of aviation weather forecasts and warnings, several NWS facilities provide aviation weather products and services to FAA and the aviation sector. These facilities include the Aviation Weather Center, weather forecast offices located across the country, and 21 center weather service units located at FAA en route centers across the country. The Aviation Weather Center located in Kansas City, Missouri, issues warnings, forecasts, and analyses of hazardous weather for aviation. Staffed by 55 personnel, the center develops warnings of hazardous weather for aircraft in flight and forecasts of weather conditions for the next 2 days that could affect both domestic and international aviation. The center also produces a Collaborative Convective Forecast Product, a graphical representation of expected thunderstorms or related conditions at 2, 4, and 6 hours. This is used by FAA to manage aviation traffic flow across the country. The Aviation Weather Center’s key products are described in table 1. NWS’s 122 weather forecast offices issue terminal area forecasts for approximately 632 locations every 6 hours or when conditions change, consisting of the expected weather conditions significant to a given airport or terminal area, and are primarily used by commercial and general aviation pilots. The terminal area forecasts are updated every 3 hours for 35 key airports and every 2 hours for the airports in New York, Atlanta, and Chicago. NWS’s center weather service units are located at each of FAA’s 21 en route centers and operate 16 hours a day, 7 days a week (see fig. 2). Each center weather service unit usually consists of three meteorologists and a meteorologist-in-charge who provide strategic advice and aviation weather forecasts to FAA traffic management personnel. Governed by an interagency agreement, FAA currently reimburses NWS approximately $13 million annually for this support. The meteorologists at the center weather service units use a variety of systems to gather and analyze information compiled from NWS and FAA weather sensors. Key systems used to compile weather information include FAA’s Weather and Radar Processor, FAA’s Integrated Terminal Weather System, FAA’s Corridor Integrated Weather System, and a remote display of NWS’s Advanced Weather Interactive Processing System. Meteorologists at several center weather service units also use NWS’s National Centers—Advanced Weather Interactive Processing System. Table 2 provides a description of key systems. NWS meteorologists at the en route centers provide several products and services to the FAA staff, including meteorological impact statements, center weather advisories, periodic briefings, and on-demand consultations. These products and services are described in table 3. In addition, center weather service unit meteorologists receive and disseminate pilot reports, provide input every 2 hours to the Aviation Weather Center’s creation of the Collaborative Convective Forecast Product, train FAA personnel on how to interpret weather information, and provide weather briefings to nearby terminal radar approach control facilities and air traffic control towers. In recent years, FAA has undertaken multiple initiatives to assess and improve the performance of the center weather service units. Studies conducted in 2003 and 2006 highlighted concerns with the lack of standardization of products and services at NWS’s center weather service units. To address these concerns, the agency sponsored studies that determined that weather data could be provided remotely using current technologies, and that private sector vendors could provide these services. In 2005, the agency requested that NWS restructure its aviation weather services by consolidating its center weather service units to a smaller number of sites, reducing personnel costs, and providing products and services 24 hours a day, 7 days a week. NWS subsequently submitted a proposal for restructuring its services, but FAA declined the proposal citing the need to refine its requirements. In December 2007, FAA issued revised requirements and asked NWS to respond with proposals defining the technical and cost implications of three operational concepts. The three concepts involved (1) on-site services provided within the existing configuration of offices located at the 21 en route centers, (2) remote services provided by a reduced number of regional facilities, and (3) remote services provided by a single centralized facility. NWS responded with three proposals, but FAA rejected these proposals in September 2008, noting that while elements of each proposal had merit, the proposed costs were too high. FAA requested that NWS revise its proposal to bring costs down while stating a preference to move toward a single center weather service unit with a backup site. As a separate initiative, NWS began a series of improvements in order to address FAA’s key concerns. Specifically, in April 2008, the agency initiated a program to improve the consistency of the center weather service units’ products and services. This program involved standardizing the technology, collaboration, and training for all 21 center weather service units and conducting site visits to evaluate and provide feedback to each unit. NWS reported that it completed these efforts in 2009. A summary of FAA’s key concerns and NWS’s efforts to address them is included in appendix II. After two requests for deadline extensions on a new proposal, NWS provided FAA with an updated proposal in June 2009 based on the two-site approach FAA had requested in September 2008. FAA responded to NWS’s proposal by requesting more information and stated that the agencies would work together to resolve issues. From September through November 2009, the agencies completed a series of meetings to address issues from the proposal and agreed that NWS would resubmit its proposal in December 2009 to consolidate the service units. In December 2009, FAA revised its requirements to reflect the agencies’ efforts aimed at improving center weather service operations. However, NWS did not submit its proposal in December 2009 to consolidate the center weather service units. According to NWS officials, they decided not to submit the proposal because (1) the NWS labor union and others raised concerns about consolidating offices, (2) NWS could implement technical improvements more quickly under the current organizational structure, and (3) the agency wanted to focus its efforts and resources on future weather system development rather than restructuring existing operations. Table 4 provides a chronology of the agencies’ assessment and improvement efforts.