Wide Area Augmentation System
WAAS is an extremely accurate
navigation system developed for civil aviation. Before WAAS, the
U.S. National Airspace System (NAS) did not have the potential to
provide horizontal and vertical navigation for approach operations
for all users at all locations. With WAAS, this capability is a reality.
WAAS provides service for all classes of aircraft in all phases of
flight - including en route navigation, airport departures, and airport
arrivals. This includes vertically-guided landing approaches in instrument
meteorological conditions at all qualified locations throughout
WAAS uses a network of precisely-located ground
reference stations that monitor Global Positioning System (GPS) satellite
signals. These stations are located throughout the continental United
States , Hawaii , Puerto Rico and Alaska ; with additional stations
being installed in Alaska , Canada and Mexico . These stations collect
and process GPS information and send this information to WAAS master
stations. The WAAS master stations develop a WAAS correction message
that is sent to user receivers via navigation transponders on geostationary
The WAAS message improves the accuracy, availability,
and integrity (safety) of GPS-derived position information. Using
WAAS, GPS signal accuracy is improved from 20 meters to approximately
1.5 - 2 meters in both the horizontal and vertical dimensions. Availability
is increased through the addition of the WAAS satellites providing
additional course correction. WAAS also eliminates the requirement
to conduct receiver autonomous integrity monitoring (RAIM) predictions.
In terms of safety, WAAS provides pilot alerting within 6 to 8 seconds
(depending on the airborne equipment) anytime the input signal for
positioning becomes unusable.
WAAS reached initial operational capability for
aviation use in the NAS on July 10, 2003 , providing navigation throughout
the entire NAS and vertically-guided approach service known as localizer
performance with vertical guidance (LPV) to the 48 contiguous states.
Initially, LPV capability enabled pilots using WAAS to descend with
stabilized vertical guidance to decision altitudes as low as 250
feet above the runway and visibility minimums as low as ½ mile
at qualified runways. In March 2006, the FAA announced the extension
of this initial capability to decision altitudes as low as 200 feet
above the runway. Since our first service delivery in 2003, our focus
has shifted to expand LPV performance to all areas of the continental
United States , most of Alaska , and most of Canada and Mexico .
This expansion will be complete in 2008.
The implementation of WAAS into the NAS will result
in safety and capacity improvements. WAAS-enabled procedures can
open more usable airspace to pilots and provide more direct routing.
WAAS will also eventually reduce operations costs for the FAA by
enabling the removal of a portion of existing ground-based navigation
WAAS is an enabler of Required Navigation Performance
(RNP); a critical component of the movement toward performance-based
navigation in the NAS. RNP is a concept of area navigation (RNAV)
operations in which the aircraft navigation system provides containment,
monitoring, and alerting for flight within a given airspace. WAAS
navigation services meet or exceed the most stringent RNP performance
values. As air traffic management becomes more global, the WAAS concept
is being applied to civil aviation infrastructure worldwide, enabling
global safety improvements. WAAS is the first of several space-based
augmentation systems being developed throughout the world and is
compatible with all other international satellite-based augmentation
systems. Moreover, with more stringent RNP standards, inefficiencies
in airspace utilization could be reduced, thus increasing traffic
flows and reducing delays.
Although the WAAS was designed for aviation users,
it supports a wide variety of non-aviation uses including agriculture,
surveying, recreation, and surface transportation, just to name a
few. The WAAS signal has been available for non safety-of-life applications
since August 24, 2000 , and numerous manufacturers have developed
WAAS-enabled GPS receivers for the consumer market. Today, there
are millions of non-aviation WAAS-enabled GPS receivers in use.
The next phase of WAAS is referred to as the Global
Navigation Satellite System Landing System (GLS) segment. The GLS
phase of WAAS is scheduled to coincide with the operational capability
of GPS modernization and is scheduled to be completed in 2013. GLS
will utilize, and depend upon, improvements that the Department of
Defense (DoD) will make as part of its GPS modernization program.
GPS modernization will enable WAAS to provide the GLS capability
during periods of severe solar storm activity and provide additional
security against interference to the GPS.
WAAS is the first of many augmentation systems
being developed throughout the world. In the future, WAAS will
be compatible with international satellite-based augmentation systems,
enabling WAAS-type augmentations worldwide.
WAAS Fact Sheet in PDF format..