The Wide Area Augmentation System (WAAS) is a satellite technology that has become essential in making air travel safer and more efficient for both private and commercial travelers. WAAS represents an enormous leap forward in air navigation. When it was first activated on July 10, 2003, WAAS allowed pilots for the first time to rely on the Global Positioning System (GPS) as a primary means of navigation. That means that pilots can use WAAS alone to navigate and land, in most instances. It is important that pilots have as accurate information as possible when landing; WAAS collects, processes, and corrects the GPS information to ensure that the data the pilot receives can be trusted.
Pilots fly into airports with the guidance of either ground-based navigational aids such as Instrument Landing Systems (ILS) or or satellite-based navigation, i.e. GPS. The FAA must develop new approach procedures for an airport before an aircraft can use WAAS. These approach procedures are called Localizer Performance with Vertical guidance (LPV). For the past 60 years, the Category-1 Instrument Landing System (ILS) has been used at airports throughout the National Airspace System to guide aircraft to as low as 200 feet above the runway surface. WAAS now provides similar capability, but at many more runway ends, without airport infrastructure requirements.
The FAA has now published more than 3,100 LPVs based on WAAS at more than 1,500 airports. This is significant because the number of approach procedures based on WAAS has now exceeded twice the number of approach procedures based on its ground-based predecessor, the Category-1 ILS.
The number of WAAS procedures will continue to grow. WAAS has enabled a new Localizer Performance (LP) approach which provides the same lateral accuracy as LPV but without the vertical guidance. The FAA expects to develop 400-500 new LPVs and LPs per year until every qualified runway in the national airspace system has one.
The WAAS signal is provided from space so there is no need for the FAA to install and maintain navigation equipment at an airport, such as that needed for an ILS. Additionally, safety is improved as more aircraft are provided with vertically-guided approaches to more runway ends. This also improves flight planning options.
The way pilots navigate and aviation in general has definitely been transformed.
By virtue of its extensive coverage area, WAAS can provide vertically-guided approach capability at thousands of airports and airstrips where this capability had previously not been available. It is also a core element in transitioning to the satellite-based air traffic control system of the future.
WAAS is designed to improve the accuracy and ensure the integrity of positioning and timing information from GPS satellites.
- GPS alone does not meet FAA’s navigation requirements for accuracy, integrity, and availability for all operations; nor does GPS provide the necessary guarantees that its signal will be accurate, available, and safe to use at all times.
- WAAS corrects for the GPS satellite position errors, ionosphere delays, and other disturbances in the GPS signals, improving the accuracy and reliability of the users’ position solution.
- More importantly, WAAS warns the pilot when the satellites are not functioning correctly and should not be used for navigation.
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 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.
WAAS was developed for the FAA by Raytheon Corporation.
How WAAS Works
WAAS uses a network of precisely located ground reference stations that monitor GPS satellite signals. These stations are located throughout the continental U.S., Hawaii, Puerto Rico, Alaska, Canada and Mexico. The stations collect and process GPS information and send the information to WAAS master stations. The WAAS master stations develop a WAAS correction message that is sent to user receivers via a ‘GPS-like’ signal from navigation transponders onboard geostationary satellites. The WAAS message improves the accuracy, availability and integrity 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. WAAS hardware consists of: 38 ground reference stations, 3 master stations, 3 geostationary satellites with navigation transponders onboard, 6 uplink stations, 2 operational control centers, and the WAAS terrestrial communications network.
Two of the FAA’s top goals are increased aircraft safety and greater air traffic capacity in a defined airspace. WAAS provides for both, along with additional significant benefits:
- More vertically-guided approach procedures, which are proven to be safer than those without vertical-guidance.
- More flexible approach and departure routings, which will cut arrival times as well as enhance safety and noise abatement.
- More direct, fuel efficient and timely routings through the air traffic control system.
- Augmented navigation source for Automatic Dependent Surveillance-Broadcast (ADS-B). Using WAAS, ADS-B can report a more accurate position to controllers and other aircraft flying in the area than can be provided by GPS alone.
- Navigation source for Terrain Avoidance Warning Systems, which warn pilots and controllers of proximity to the ground.
- Significant government cost savings due to the elimination of maintenance costs associated with older, more expensive ground-based navigation aids.
- Does not require any additional runway infrastructure.
WAAS is a pioneering technology. Currently, no other navigation technologies exist to meet FAA requirements and user needs for the expansion of vertically-guided landing capabilities at thousands of additional airports.
- July 2003 — WAAS is commissioned by the FAA for instrument flight use supporting minimums as low as 250’.
- September 2003 — The first WAAS LPVs are published.
- October 2004 — FAA Administrator Marion C. Blakey announces that U.S. avionics manufacturers are building new WAAS receivers or upgrading existing GPS receivers to WAAS capability and urges aviation users to equip.
- December 2004 – The FAA installs four additional WAAS reference stations in Barrow, Bethel, Fairbanks, and Kotzebue, AK as initial steps in a planned WAAS expansion.
- March 2005 — The FAA finalizes a Geostationary Satellite Communications Control Segment contract with Lockheed Martin for WAAS geostationary satellite leased services through 2016.
- June 2005 — The first international WAAS reference station is installed in Canada.
- March 2006–Due to outstanding system performance, WAAS is approved to support lower minimums, as low as 200’.
- August 2006 — WAAS service is expanded to cover all of Alaska.
- November 2006 — A new WAAS GEO, the PanAmSat Galaxy XV, is integrated into WAAS, increasing WAAS availability throughout the U.S.
- July 2007 — A second new WAAS GEO, the Telesat ANIK-F1R, is integrated into WAAS, completing the implementation of enhanced WAAS GEO coverage. Later in the same year, the original WAAS Inmarsat GEOs are phased out.
- September 2007 — WAAS service is expanded to cover large portions of Canada and Mexico.
- August 2008– Final Full LPV release integrated into the WAAS, improving service availability to the WAAS and initiating LPV-200 service.
- September 2008– Awarded WAAS Follow-on Contract to the incumbent WAAS contractor to support WAAS technology refresh and to migrate maintenance capability to the FAA’s maintenance organization
- October 2011 – Third WAAS GEO, the Inmarsat I4F3, is integrated in WAAS providing a ‘3 for 2’ WAAS GEO Satellite constellation which improves computed WAAS availability and continuity of operation.
- October 2012– WAAS algorithmic and ionospheric modeling improvements fielded to improve WAAS robustness and availability ahead of the upcoming increase in Solar activity
- September 2012 – Contract is awarded for two new GEOs to replace two operational satellites nearing the end of their 10 year service leases.
- May 2013 — The number of runways served by WAAS LPVs exceeds twice the number of runways served by ILS.
- May 2013 — The number of WAAS LPV-capable avionics passes the 90,000 mark and continues to climb steadily each month.