MAINTAINING RUNWAY USE IN REDUCED VISIBILITY

Although traffic in congested airspace typically operates under instrument flight rules (IFR), adverse weather and actual instrument meteorological conditions (IMC) can drastically reduce system capacity. Many parallel runways cannot be used simultaneously in IMC because of the time delay and limited accuracy of terminal area radar, and the runways are spaced closer than the minimum allowable distance for wake vortex separation.

LAAS AND WAAS IMPLEMENTATION

The wide area augmentation system (WAAS) became available at most locations in 2003. Additional ground reference stations are expected to become operational in Canada, Mexico, and Alaska by 2008, providing more complete WAAS coverage for the continental United States. The local area augmentation system (LAAS) provides even greater accuracy and may be certified for use in precision approaches at some locations beginning in 2007.

Another benefit of LAAS and WAAS is that better position information can be sent to controllers and other aircraft. Automatic dependant surveillancebroadcast (ADS-B) uses GPS to provide much more accurate location information than radar and transponder systems. This position information is broadcast to other ADS-equipped aircraft (as well as ground facilities), providing pilots and controllers with a more accurate real-time picture of traffic.

For full safety and effectiveness, every aircraft under the control of ATC will need ADS-B. Until that occurs, controllers must deal with a mix of ADS-B and transponder-equipped aircraft. Equipment is already available that can fuse the information from both sources and show it on the same display. Traffic information service-broadcast (TIS-B) does just that. Although TIS-B is primarily intended for use on the ground by controllers, the information can be transmitted to suitably equipped aircraft and displayed to pilots in the cockpit. The cockpit display of traffic information (CDTI) provides information for both ADS-B and non-ADS-B aircraft on a single cockpit display. [Figure 6-7] Since this information is shown even while the aircraft is on the ground, it also improves situational awareness during surface movement, and can help prevent or resolve taxiing conflicts.