Editing Wide Area Augmentation System (section)

==History and development==
{{More citations needed section|date=December 2006}}
The WAAS was jointly developed by the United States Department of Transportation (DOT) and the Federal Aviation Administration (FAA) as part of the [http://gauss.gge.unb.ca/us1996frp.pdf 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.<ref name="FAA_WAAS_FAQ" /> Without WAAS, ionospheric disturbances, [[clock drift]], and satellite orbit errors create too much error and uncertainty in the GPS signal to meet the requirements for a [[precision approach]] (see [[Gps#Accuracy and error sources|GPS sources of error]]). A precision approach includes altitude information and provides course guidance, distance from the runway, and elevation information at all points along the approach, usually down to lower altitudes and weather minimums than non-precision approaches.

Prior to the WAAS, the U.S. National Airspace System (NAS) did not have the ability to provide lateral and vertical navigation for precision approaches for all users at all locations. The traditional system for precision approaches is the [[instrument landing system]] (ILS), which used a series of radio transmitters each broadcasting a single signal to the aircraft. This complex series of radios needs to be installed at every runway end, some offsite, along a line extended from the runway centerline, making the implementation of a precision approach both difficult and very expensive. The ILS system is composed of 180 different transmitting antennas at each point built. 

For some time the FAA and [[NASA]] developed a much improved system, the [[microwave landing system]] (MLS). The entire MLS system for a particular approach was isolated in one or two boxes located beside the runway, dramatically reducing the cost of implementation. MLS also offered a number of practical advantages that eased traffic considerations, both for aircraft and radio channels. Unfortunately, MLS would also require every airport and aircraft to upgrade their equipment.

During the development of MLS, consumer GPS receivers of various quality started appearing. GPS offered a huge number of advantages to the pilot, combining all of an aircraft's long-distance navigation systems into a single easy-to-use system, often small enough to be hand held. Deploying an aircraft navigation system based on GPS was largely a problem of developing new techniques and standards, as opposed to new equipment. The FAA started planning to shut down their existing long-distance systems ([[VHF omnidirectional range|VOR]] and [[Non-directional beacon|NDB]]s) in favor of GPS. This left the problem of approaches, however. GPS is simply not accurate enough to replace ILS systems. Typical accuracy is about {{convert|15|m}}, whereas even a "CAT I" approach, the least demanding, requires a vertical accuracy of {{convert|4|m}}.

This inaccuracy in GPS is mostly due to large "billows" in the [[ionosphere]], which slow the radio signal from the satellites by a random amount. Since GPS relies on timing the signals to measure distances, this slowing of the signal makes the satellite appear farther away. The billows move slowly, and can be characterized using a variety of methods from the ground, or by examining the GPS signals themselves. By broadcasting this information to GPS receivers every minute or so, this source of error can be significantly reduced.
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This led to the concept of [[Differential GPS]], which used separate radio systems to broadcast the correction signal to receivers. Aircraft could then install a receiver which would be plugged into the GPS unit, the signal being broadcast on a variety of frequencies for different users (FM radio for cars, longwave for ships, etc.). Broadcasters of the required power generally cluster around larger cities, making such DGPS systems less useful for wide-area navigation. Additionally, most radio signals are either line-of-sight, or can be distorted by the ground, which made DGPS difficult to use as a precision approach system or when flying low for other reasons.

The FAA considered systems that could allow the same correction signals to be broadcast over a much wider area, such as from a satellite, leading directly to WAAS. Since a GPS unit already consists of a satellite receiver, it made much more sense to send out the correction signals on the same frequencies used by GPS units, than to use an entirely separate system and thereby double the probability of failure. In addition to lowering implementation costs by "piggybacking" on a planned satellite launch, this also allowed the signal to be broadcast from [[geostationary orbit]], which meant a small number of satellites could cover all of North America.

On July 10, 2003, the WAAS signal was activated for general aviation, covering 95% of the United States, and portions of Alaska offering {{convert|350|ft}} minimums.

On January 17, 2008, Alabama-based Hickok & Associates became the first designer of helicopter WAAS with Localizer Performance (LP) and [[Localizer Performance with Vertical guidance]] (LPV) approaches, and the only entity with FAA-approved criteria (which even FAA has yet to develop).<ref>{{Cite web |url=http://www.ainonline.com/news/single-news-page/article/waas-approaches-coming-to-heliports/?no_cache=1&cHash=a7ee70cd1a |title = WAAS approaches coming to heliports: AINonline |archive-url=https://archive.today/20110616214831/http://www.ainonline.com/news/single-news-page/article/waas-approaches-coming-to-heliports/?no_cache=1&cHash=a7ee70cd1a |archive-date=16 June 2011 |url-status=dead}}</ref><ref>{{cite web | url=http://www.flttechonline.com/Current/Hickok%20and%20Associates%20Developing%20WAAS%20Approaches%20for%20Helicopters.htm | title=Top of world Crypto Gambling | access-date=2010-02-02 | archive-date=2013-09-22 | archive-url=https://web.archive.org/web/20130922150758/http://www.flttechonline.com/Current/Hickok%20and%20Associates%20Developing%20WAAS%20Approaches%20for%20Helicopters.htm | url-status=dead }}</ref><ref>https://archive.today/20110707100623/http://www.ainonline.com/ain-and-ainalerts/aviation-international-news/single-publication-story/browse/0/article/owners-responsible-for-private-helo-approaches/?no_cache=1&tx_ttnews [mode]=1</ref> 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<ref>{{cite web|url=http://www.alaskasworld.com/newsroom/QXnews/QXstories/QX_20100108_104108.asp|title=Horizon Makes Aviation History with First WAAS Flight|access-date=2010-01-13|archive-date=2010-01-12|archive-url=https://web.archive.org/web/20100112113104/http://www.alaskasworld.com/newsroom/QXnews/QXstories/QX_20100108_104108.asp|url-status=dead}}</ref> 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.{{update inline|date=May 2024}}

===Timeline===
'''Wide-Area Augmentation System (WAAS) timeline'''
<timeline>
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DateFormat = mm/dd/yyyy
TimeAxis   = orientation:vertical order:normal format:yyyy
Period     = from:1995 till:2022
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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."
</timeline><ref>* [http://www.defensedaily.com/cgi/rw/show_mag.cgi?pub=av&mon=0303&file=0303capstone.htm Capstone program testing] {{Webarchive|url=https://web.archive.org/web/20120206011224/http://www.defensedaily.com/cgi/rw/show_mag.cgi?pub=av&mon=0303&file=0303capstone.htm |date=2012-02-06 }}
* Inmarsat moves AOR-W Satellite #35 east Federal Aviation Administration. [http://gps.faa.gov/programs/waas/for_pilots.htm Information for Pilots]. Accessed 12 June 2006.
* Contract with [[Hughes Aircraft]] finalized [http://www.hq.nasa.gov/office/pao/History/presrep96/Presrp96/ch6b.htm First reference] {{Webarchive|url=https://web.archive.org/web/20150922214905/http://www.hq.nasa.gov/office/pao/History/presrep96/Presrp96/ch6b.htm |date=2015-09-22 }},  [http://www.fas.org/spp/military/gao/rced98012.htm Second reference] {{Webarchive|url=https://web.archive.org/web/20160311202204/http://fas.org/spp/military/gao/rced98012.htm |date=2016-03-11 }} 
* [http://www.hq.nasa.gov/office/pao/History/presrep96/Presrp96/ch6b.htm Version 1.5 Released] 
* General source: Federal Aviation Administration. [http://gps.faa.gov/programs/waas/currentnews-text.htm WAAS Current news]. Accessed June 12, 2006.</ref>