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.