sources that include: pilot reports; sensors whose data are provided by the FAA, the National Weather Service, and commercial vendors; aircraft sensors whose data are reported through the aircraft communication addressing and reporting system (ACARS); surface sensors, including wind shear sensors, operated by the FAA in the vicinity of airports; and primary radar, which is used to detect phenomena such as wind shear and thunderstorms. Surface weather observations are also generated by the automated weather observing system (AWOS) and the automated surface observing system (ASOS).

Weather data are processed and presented to controllers, traffic management specialists, and flight service specialists through a variety of systems. Controllers and flight service specialists, in turn, communicate with pilots to exchange weather information. The current system of weather information distribution for air traffic control is fragmented and does not adequately tailor information for controllers, specialists, and pilots. Therefore, the FAA is developing or planning automated features that would integrate weather data and distribute it to controllers, specialists, and pilots. Future systems would also include improved predictive capabilities and would support responses to weather conditions (Federal Aviation Administration, 1996a). Figure 3.1 summarizes current and contemplated systems for processing, displaying, and communicating weather data pertinent to air traffic control. The figure summarizes, for key data processing systems, the sources of data, the types of data processed, media by which controllers and specialists receive the data, and mechanisms by which the data are transmitted to pilots. These elements are discussed below from the perspectives of controllers and specialists within the terminal (tower and TRACON) and en route (including oceanic) environments, and then from the perspective of the pilots.

Controllers and traffic managers in the terminal environment, which includes tower and TRACON facilities, receive weather reports from pilots (through pilot reports), from the National Weather Service, and from commercial vendors. They also receive automated support through three systems: the automated weather observing system and automated surface observing system (AWOS/ASOS), the low-level wind shear alert system (LLWAS), and the terminal Doppler weather radar (TDWR).

The AWOS/ASOS collects data from ground sensors and provides surface weather observations to tower controllers and TRACON specialists via an automated surface observing system display. The low-level wind shear alert system processes real-time data from pole-mounted sensors in the airport vicinity to determine wind shear and microburst conditions. The alert system presents these data, along with applicable alerts, to both tower and TRACON controllers via