Wide Area Augmentation System

Accuracy A primary goal of WAAS was to allow aircraft to make a Category I approach without any equipment being installed at the airport. This would allow new GPS-based instrument landing approaches to be developed for any airport, even ones without any ground equipment. A Category I approach requires an accuracy of laterally and vertically. FAA fact sheets and guidance on WAAS note that it enables thousands of instrument approach procedures in the United States, including LPV and LP procedures, and is often used to provide vertically guided minima comparable in concept (though not identical in standards) to precision-approach operations at airports without an ILS. To meet this goal, the WAAS specification requires it to provide a position accuracy of or less (for both lateral and vertical measurements), at least 95% of the time. Actual performance measurements of the system at specific locations have shown it typically provides better than laterally and vertically throughout most of the contiguous United States and large parts of Canada and Alaska. Integrity Integrity of a navigation system includes the ability to provide timely warnings when its signal is providing misleading data that could potentially create hazards. The WAAS specification requires the system detect errors in the GPS or WAAS network and notify users within 6.2 seconds. Availability Availability is the probability that a navigation system meets the accuracy and integrity requirements. Before the advent of WAAS, GPS specifications allowed for system unavailability for as much as a total time of four days per year (99% availability). The WAAS specification mandates availability as 99.999% (five nines) throughout the service area, equivalent to a downtime of just over 5 minutes per year. ==Operation==

WAAS is composed of three main segments: the ground segment, space segment, and user segment. Ground segment The ground segment is composed of multiple wide-area reference stations (WRS). These precisely surveyed ground stations monitor and collect information on the GPS signals, then send their data to three wide-area master stations (WMS) using a terrestrial communications network. The reference stations also monitor signals from WAAS geostationary satellites, providing integrity information regarding them as well. As of October 2007 there were 38 WRSs: twenty in the contiguous United States (CONUS), seven in Alaska, one in Hawaii, one in Puerto Rico, five in Mexico, and four in Canada. Using the data from the WRS sites, the WMSs generate two different sets of corrections: fast and slow. The fast corrections are for errors which are changing rapidly and primarily concern the GPS satellites' instantaneous positions and clock errors. These corrections are considered user position-independent, which means they can be applied instantly by any receiver inside the WAAS broadcast footprint. The slow corrections include long-term ephemeric and clock error estimates, as well as ionospheric delay information. WAAS supplies delay corrections for a number of points (organized in a grid pattern) across the WAAS service area (see user segment below to understand how these corrections are used). Once these correction messages are generated, the WMSs send them to two pairs of ground uplink stations (GUS), which then transmit to satellites in the space segment for rebroadcast to the user segment. Reference stations Each FAA Air Route Traffic Control Center in the 50 states has a WAAS reference station, except for Indianapolis. There are also stations positioned in Canada, Mexico and Puerto Rico. Space segment The space segment consists of multiple communication satellites which broadcast the correction messages generated by the WAAS master stations for reception by the user segment. The satellites also broadcast the same type of range information as normal GPS satellites, effectively increasing the number of satellites available for a position fix. The space segment currently consists of three commercial satellites: Eutelsat 117 West B, SES-15, and Galaxy 30. Satellite history The original two WAAS satellites, named Pacific Ocean Region (POR) and Atlantic Ocean Region-West (AOR-W), were leased space on Inmarsat III satellites. These satellites ceased WAAS transmissions on July 31, 2007. With the end of the Inmarsat lease approaching, two new satellites (Galaxy 15 and Anik F1R) were launched in late 2005. Galaxy 15 is a PanAmSat and Anik F1R is a Telesat. As with the previous satellites, these are leased services under the FAA's Geostationary Satellite Communications Control Segment contract with Lockheed Martin for WAAS geostationary satellite leased services, who were contracted to provide up to three satellites through the year 2016. A third satellite was later added to the system. From March to November 2010, the FAA broadcast a WAAS test signal on a leased transponder on the Inmarsat-4 F3 satellite. The test signal was not usable for navigation, but could be received and was reported with the identification numbers PRN 133 (NMEA #46). In November 2010, the signal was certified as operational and made available for navigation. Following in orbit testing, Eutelsat 117 West B, broadcasting signal on PRN 131 (NMEA #44), was certified as operational and made available for navigation on March 27, 2018. The SES 15 satellite was launched on May 18, 2017, and following an in-orbit test of several months, was set operational on July 15, 2019. In 2018, a contract was awarded to place a WAAS L-band payload on the Galaxy 30 satellite. The satellite was successfully launched on August 15, 2020, and the WAAS transmissions were set operational on April 26, 2022, re-using PRN 135 (NMEA #48). After approximately three weeks with four active WAAS satellites, operational WAAS transmissions on Anik F1-R were ended on May 17, 2022. ==History and development==

The WAAS was jointly developed by the United States Department of Transportation (DOT) and the Federal Aviation Administration (FAA) as part of the Federal Radionavigation Program (DOT-VNTSC-RSPA-95-1/DOD-4650.5), beginning in 1994, to provide performance comparable to category 1 instrument landing system (ILS) for all aircraft possessing the appropriately certified equipment. This helicopter WAAS criteria offers as low as 250 foot minimums and decreased visibility requirements to enable missions previously not possible. On April 1, 2009, FAA AFS-400 approved the first three helicopter WAAS GPS approach procedures for Hickok & Associates' customer California Shock/Trauma Air Rescue (CALSTAR). Since then they have designed many approved WAAS helicopter approaches for various EMS hospitals and air providers, within the United States as well as in other countries and continents. On December 30, 2009, Seattle-based Horizon Air flew the first scheduled-passenger service flight using WAAS with LPV on flight 2014, a Portland to Seattle flight operated by a Bombardier Q400 with a WAAS FMS from Universal Avionics. The airline, in partnership with the FAA, will outfit seven Q400-aircraft with WAAS and share flight data to better determine the suitability of WAAS in scheduled air service applications. Timeline Wide-Area Augmentation System (WAAS) timeline ImageSize = width:700 height:1000 PlotArea = left:40 right:30 top:10 bottom:20 DateFormat = mm/dd/yyyy TimeAxis = orientation:vertical order:normal format:yyyy Period = from:1995 till:2022 AlignBars = early ScaleMajor = unit:year increment:1 start:1995 ScaleMinor = unit:month increment:6 start:06/01/1995 Colors = id:gray value:gray(0.7) • there is no automatic collision detection, • so shift texts up or down manually to avoid overlap Define $dx = 25 # shift text to right side of bar PlotData = bar:event width:20 color:blue shift:($dx,-4) from:start till:end color:blue mark:(line, white) at:08/01/1995 text:"August, 1995: Wilcox Electric contracted to deliver WAAS." at:02/01/1996 text:"February, 1996: WAAS Architecture Version 1.5 Released." at:04/01/1996 shift:($dx,1.5) text:"April, 1996: Wilcox contract terminated due to inadequate technical capability by Wilcox." at:10/01/1996 text:"October, 1996: Hughes Aircraft contracted to deliver Phase 1 WAAS by April 1, 1999." at:12/18/1996 shift:($dx,0.5) text:"December, 1996: Inmarsat's POR (NMEA #47) is launched." at:06/03/1997 text:"June, 1997: Inmarsat's AOR-W (NMEA #35) is launched." at:01/01/1998 text:"January, 1998: Raytheon Systems purchases Hughes Aircraft, assuming control of WAAS contract." at:12/01/1999 text:"December, 1999: WAAS signal being transmitted from satellites for testing purposes." at:03/31/2003 text:"March 31, 2003: Capstone conducts the first commercial flight with a TSO-145 GPS/WAAS receiver." at:07/10/2003 text:"July 10, 2003: The FAA commissions the Wide Area Augmentation System (WAAS) for aviation use." at:09/01/2004 shift:($dx,-15) text:"September, 2004: Site surveys for new WAAS reference stations (WRS) in Alaska and Canada are completed." at:10/01/2004 text:"October, 2004: The FAA approves the Garmin 480 as the first WAAS-equipped avionics for LPV approaches." at:03/01/2005 text:"March, 2005: The FAA selects Lockheed Martin as new Ground Control Contractor." at:06/01/2005 text:"June, 2005: First international Wide-area Reference Station Installed in Gander, Newfoundland & Labrador, Canada." at:09/09/2005 text:"September 9, 2005: Telesat's Anik F1R (NMEA #51) is launched." at:10/13/2005 shift:($dx,5) text:"October 13, 2005: PanAmSat's Galaxy XV (NMEA #48) is launched." at:02/01/2006 shift:($dx,2) text:"February, 2006: Inmarsat's AOR-W (NMEA #35) moved from 54°W to 142°W, interrupting service for the northeastern United States." at:03/01/2006 shift:($dx,10) text:"March, 2006: WAAS approved to provide guidance down to 200 feet above an airport’s surface for LPV instrument approaches." at:11/09/2006 text:"Galaxy XV (NMEA #48) begins broadcasting certified correction messages, restoring service for the northeastern United States." at:09/27/2007 text:"New Wide-area Reference Stations in Mexico and Canada come online, expanding WAAS service area." at:06/15/2016 text:"June 15, 2016: Eutelsat 117 West B (Satmex 9; NMEA #44) is launched by SpaceX." at:05/18/2017 text:"May 18, 2017: Boeing SES-15 is launched by Arianespace." at:11/09/2017 text:"November, 2017: Inmarsat 4-F3 (AMR; NMEA #46) removed from WAAS satellite mask." at:08/15/2020 text:"August 15, 2020: Galaxy 30 is launched by Arianespace." at:04/26/2022 text:"April 26, 2022: Galaxy 30 (NMEA #48) added to WAAS satellite mask." at:05/17/2022 shift:($dx, 4.0) text:"May 17, 2022: Anik F1R (NMEA #51) removed from WAAS satellite mask." ==Comparison of accuracy==

WAAS addresses all of the "navigation problem", providing highly accurate positioning that is extremely easy to use, for the cost of a single receiver installed on the aircraft. Ground- and space-based infrastructure is relatively limited, and no on-airport system is needed. WAAS allows a precision approach to be published for any airport, for the cost of developing the procedures and publishing the new approach plates. This means that almost any airport can have a precision approach and the cost of implementation is drastically reduced. Additionally WAAS works just as well between airports. This allows the aircraft to fly directly from one airport to another, as opposed to following routes based on ground-based signals. This can cut route distances considerably in some cases, saving both time and fuel. In addition, because of its ability to provide information on the accuracy of each GPS satellite's information, aircraft equipped with WAAS are permitted to fly at lower en-route altitudes than was possible with ground-based systems, which were often blocked by terrain of varying elevation. This enables pilots to safely fly at lower altitudes, not having to rely on ground-based systems. For unpressurized aircraft, this conserves oxygen and enhances safety. The above benefits create not only convenience, but also have the potential to generate significant cost savings. The cost to provide the WAAS signal, serving all 5,400 public use airports, is just under US$50 million per year. In comparison, the current ground based systems such as the Instrument Landing System (ILS), installed at only 600 airports, cost US$82 million in annual maintenance. Without ground navigation hardware to purchase, the total cost of publishing a runway's WAAS approach is approximately US$50,000; compared to the $1,000,000 to $1,500,000 cost to install an ILS radio system. ==Drawbacks and limitations==

For all its benefits, WAAS is not without drawbacks and critical limitations: • Space weather. All man-made satellite systems are subject to space weather and space debris threats. For example, a solar super-storm event composed of an extremely large and fast earthbound coronal mass ejection (CME) could disable the geosynchronous or GPS satellite elements of WAAS. • The broadcasting satellites are geostationary, which causes them to be less than 10° above the horizon for locations north of 71.4° latitude. This means aircraft in areas of Alaska or northern Canada may have difficulty maintaining a lock on the WAAS signal. • To calculate an ionospheric grid point's delay, that point must be located between a satellite and a reference station. The low number of satellites and ground stations limit the number of points which can be calculated. • Aircraft conducting WAAS approaches use certified GPS receivers, which are much more expensive than non-certified units. In 2024, Garmin's least expensive certified receiver, the GPS 175, had a suggested retail price of US$5,895. • WAAS is not capable of the accuracies required for Category II or III ILS approaches. Thus, WAAS is not a sole-solution and either existing ILS equipment must be maintained or it must be replaced by new systems, such as the local-area augmentation system (LAAS). • WAAS Localizer Performance with Vertical guidance (LPV) approaches with 200-foot minimums (LPV-200) will not be published for airports without medium intensity lighting, precision runway markings and a parallel taxiway. Smaller airports, which currently may not have these features, would have to upgrade their facilities or require pilots to use higher minimums. • As precision increases and error approaches zero, the navigation paradox states that there is an increased collision risk, as the likelihood of two craft occupying the same space on the shortest distance line between two navigational points has increased. ==Future of WAAS==

Improvement to aviation operations In 2007, WAAS vertical guidance was projected to be available nearly all the time (greater than 99%), and its coverage encompasses the full continental U.S., most of Alaska, northern Mexico, and southern Canada. At that time, the accuracy of WAAS would meet or exceed the requirements for Category 1 ILS approaches, namely, three-dimensional position information down to 200 feet (60 m) above touchdown zone elevation. == Applications in general and rotorcraft aviation ==

WAAS has been widely adopted in general aviation as a primary means of navigation and for flying localizer performance with vertical guidance (LPV) approaches at airports that do not have instrument landing system (ILS) equipment. The increased accuracy and integrity provided by WAAS enable approach procedures with decision altitudes as low as 200 feet at many smaller aerodromes. In addition, WAAS-supported procedures are increasingly used in rotorcraft operations to provide vertically guided approaches to heliports and hospital landing pads, improving access in poor weather and complex terrain. ==See also==