The Role of ITWS in the National Airspace System (NAS) Modernization

Weather systems will play an important role in the FAA modernization, as weather information services are critical to improving safety and enhancing the capacity of the NAS. The 1999 Aviation Capacity Enhancement Plan reveals that delays due to adverse weather, a major factor affecting NAS capacity, increased significantly from 1997 to 1998 accounting for 72 percent of system delays greater than 15 minutes.

The deployment of the Integrated Terminal Weather System (ITWS) vastly improves the FAA's ability to monitor and predict aviation-impacting weather. Its accurate forecasts of wind shifts associated with frontal passage across airport runways will enable terminal controllers and traffic managers to more efficiently sequence aircraft in and out of terminal airspace, thereby mitigating weather-induced reductions on NAS capacity. Furthermore, the wind shear and microburst predictive capability of ITWS will improve NAS safety. ITWS will provide significant and timely information on severe storms that assist controllers/traffic managers in routing aircraft around hazardous weather. In addition to displaying enhanced weather products to terminal personnel, ITWS will provide enhanced terminal weather forecast data to terminal automation systems. This will improve the performance of the automation systems (or tools) used by terminal personnel. ITWS situation displays located in the Air Traffic Control System Command Center and Air Route Traffic Control Centers will enhance traffic flow management across the NAS.

ITWS will function as a "weather server" at 45 major airports. It will ingest NWS Rapid Update Cycle (RUC II) gridded forecast data, Meteorological Data Collection and Reporting System (MDCRS) aircraft observations, and lightning data. ITWS will also acquire and process data from sensors such as the WSR-88D (or NEXRAD), Terminal Doppler Weather Radar (TDWR), Low Level Wind Shear Alert System (LLWAS), and Airport Surveillance Radar (ASR-9). ITWS then generates products for NAS non-meteorologist users and the Center TRACON Automation System (CTAS). It will also process ASR-9 data to remove anomalous propagation and ground clutter. The Terminal Weather Information for Pilots (TWIP) functionally will be enhanced through the addition of ITWS products. TWIP is a prototype system that currently provides airline pilots with a coarse graphical depiction of hazardous weather at TDWR sites.

The FAA is validating emerging user requirements for ITWS data. In addition, it is evaluating communications alternatives to meet currently validated requirements. Sufficient flexibility will be built into the system to meet the needs of new users while accommodating changing requirements of current users. However, users must be aware that developing algorithms are being tested in the current ITWS prototypes, and that some of these capabilities will not be available in the initial productions units, but will be added later as preplanned product improvements. Some of these include the incorporation of satellite data and the implementation of algorithms for vertical wind shear, storm growth and decay, icing aloft in the terminal area, in-flight icing, and visibility & ceiling predictions. Also, the FAA plans to expand the ITWS predictive capability from 30 minutes out to six hours, which will significantly enhance cross-country traffic flow. Decisions will also be made on the best way to incorporate the anticipated 10-km Eta and 20-km RUC models.