Wide Area Augmentation System (WAAS)
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The Wide Area Augmentation System (WAAS) is a critical component of the
FAA’s strategic objective of a seamless satellite navigation system
for civil aviation. The system was commissioned on July 10, 2003. This
system improves the accuracy, availability, and integrity of GPS thereby
improving the capacity and safety formerly provided by the National Airspace
System. Ultimately, WAAS will allow GPS to be used as a primary means
of navigation from takeoff through Category I precision approach.
Unlike traditional ground-based navigation aids, WAAS covers a more extensive
service area. Wide area ground reference stations (WRS) have been linked
to form a U.S. WAAS network. Signals from GPS satellites are received
by these precisely surveyed ground reference stations and any errors in
the signals are identified. Each station in the network relays the data
to one of two wide area master stations (WMS) where correction information
for specific geographical areas is computed. A correction message is prepared
and uplinked to a geostationary communications satellite (GEO) via a ground
uplink station (GUS). This message is broadcast on the same frequency
as GPS (L1, 1575.42 MHz) to GPS/WAAS receivers on board aircraft flying
within the broadcast coverage area of WAAS. Other modes of transportation
also benefit from the increased accuracy, availability, and integrity
that WAAS delivers. The WAAS broadcast message improves GPS signal accuracy
from 100 meters to approximately 3 meters (95%).
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Planned expansion of the U.S. network will include Canada, Iceland, Mexico,
and Panama, and has the potential to expand to other countries as well.
Additionally, Japan and Europe are building similar systems which are
planned to be interoperable with the U.S. WAAS. The merging of these systems
will create a worldwide seamless navigation capability similar to GPS,
but with greater accuracy, availability and integrity.
Additionally, the FAA is involved in the International Civil Aviation
Organization’s (ICAO) Global Navigation Satellite System Panel (GNSS-P)
which supports the development of standards and procedures for satellite
navigation for civil aviation applications worldwide.
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Since June 4,1998, the WAAS site installation of 25 WRSs, 2 WMSs, 4 GUSs,
and the required terrestrial communications to support the WAAS network
have been complete. Prior to the commissioning of the WAAS for aviation
for Instrument Flight Rule (IFR), the FAA conducted a series of activities
including developmental testing and evaluation, and operational testing
and evaluation of the system. WAAS now provides pilots with enroute navigation
over the United States and vertical guidance for approaches to a limited
number of runways. The FAA plans to publish approximately 300 new approaches
every year with WAAS-based vertical guidance.
For further information regarding WAAS, please contact:
WAAS Product Team, AND-730
800 Independence Avenue, SW
Washington, DC 20591
Fax: 202-493-5031