Wide Area Augmentation System


Wide Area Augmentation System

Benefits

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 dramatically 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. Whereas the current ground based systems like the traditional Instrument Landing System (ILS), installed at only 600 airports, cost US$82 million in annual maintenance.Fact|date=January 2008 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.Aircraft Owners and Pilots Association, [http://www.aopa.org/whatsnew/newsitems/2006/060307waas.html AOPA welcomes improved WAAS minimums] . March 7, 2006. Accessed January 6, 2008.]

Further savings can come from the nighttime closure of airport towers with a low volume of traffic. The FAA is reviewing 48 towers for such a potential reduction of services, which it estimates will save around US$100,000 per year at each tower, for a total annual savings of nearly US$5 million. [http://www.house.gov/transportation/aviation/05-04-05/boyer.pdf Testimony to US House Aviation Subcommitte] by Phil Boyer, dated May 4, 2005]

Drawbacks and Limitations

For all its benefits, WAAS is not without drawbacks and critical limitations.
* 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. [Department of Aeronautics and Astronautics, Stanford University. [http://waas.stanford.edu/~wwu/papers/gps/PDF/LoPLANS02.pdf WAAS Performance in the 2001 Alaska Flight Trials of the High Speed Loran Data Channel] . Accessed June 12, 2006.]
* 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 must possess certified GPS receivers, which are much more expensive than commercial units. In 2006, Garmin's least expensive certified receiver, the GNS 430W, had a suggested retail price of US$10,750.Garmin International [http://www.garmin.com/pressroom/aviation/110906.html Press Release] dated November 9, 2006.]
* 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). [Federal Aviation Administration. [http://gps.faa.gov/FAQ/faq-waas.htm WAAS FAQ] . Accessed June 12, 2006.]
* WAAS Lateral Precision Performance with Vertical guidance (LPV) approaches with 200-foot minimums 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.
* The 2004 baseline estimates the final program cost to the US Federal government as over US$3.3 billion when delivered in 2013; more than 3.7 times the original budget and 12 years behind schedule. [ [http://www.house.gov/transportation/aviation/04-14-05/mead.pdf Testimony to US House Aviation Subcommittee] by US DOT Inspector General Kenneth Mead, pages 18 and 21, dated April 14, 2005.]

The 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. [Federal Aviation Administration. [http://gps.faa.gov/programs/waas/questionsanswers.htm WAAS 200ft Minimum Related Questions and Answers] . Accessed June 12, 2006.] 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 above touchdown zone elevation. With these projections, the FAA announced on March 24, 2006 that the first procedures that allow operations down to 200 feet would be published in 2007. [Federal Aviation Administration (FAA), Press Release [http://www.faa.gov/news/press_releases/news_story.cfm?contentKey=4006 FAA Announces Major Milestone for Wide Area Augmentation System (WAAS)] . March 24, 2006.]

Software Improvements

Software improvements, to be implemented by September 2008, significantly improve signal availability of vertical guidance throughout the CONUS and Alaska. Area covered by the 95% available LPV solution in Alaska improves from 62% to 86%. And in the CONUS, the 100% availability LPV-200 coverage rises from 48% to 84%, with 100% coverage of the LPV solution.

pace Segment Upgrades

Both Galaxy XV (PRN #135) and Anik F1R (PRN #138) contain an L1 & L5 GPS payload. This means they will potentially be usable with the L5 modernized GPS signals when the new signals and receivers become available. With L5, avionics will be able to use a combination of signals to provide the most accurate service possible, thereby increasing availability of the service. These avionics systems will use ionospheric corrections broadcast by WAAS, or self-generated onboard dual frequency corrections, depending on which one is more accurate.Federal Aviation Administration (FAA), [http://gps.faa.gov/gpsbasics/GPSmodernization-text.htm GPS Modernization] Page. Accessed 29 November, 2006.] Additionally, FAA status presentations indicate a third geostationary satellite could be acquired between 2009 and 2013.

ee also

* Satellite Based Augmentation System (SBAS)
* CDGPS Canadian Differential GPS
* Quasi-Zenith Satellite System (QZSS)
* Local Area Augmentation System (LAAS)
* Joint Precision Approach and Landing System (JPALS)
* Distance Measuring Equipment (DME)
* Instrument flight rules (IFR)
* Instrument Landing System (ILS)
* GPS and Geo Augmented Navigation (GAGAN)
* LORAN
* Microwave Landing System (MLS)
* Non-Directional Beacon (NDB)
* Tactical Air Navigation (TACAN)
* Transponder Landing System (TLS)
* VHF Omni-directional Range (VOR)

References

* U.S. Department Of Transportation & Federal Aviation Administration, [http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/library/documents/media/waas/2892bC2a.pdf Specification for the Wide Area Augmentation System (WAAS)]

External links

* FAA's [http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/ WAAS program]
* Garmin's [http://www.garmin.com/aboutGPS/waas.html What is WAAS?]
* US Government's [http://www.navcen.uscg.gov/pubs/frp2005/default.htm 2005 Federal Radionavigation Plan (FRP)]
* [http://members.shaw.ca/pdops/WAAS.html WAAS coverage in Canada]


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