In September 2008, the FAA passed a key milestone in its transition from a ground-based navigation infrastructure to an infrastructure based on satellites. The FAA has now published 1,333 Localizer Performance with Vertical guidance (LPV) approach procedures which are based on the Wide Area Augmentation System (WAAS), a space-based navigation system commissioned in 2003. This is significant as the number of approach procedures based on WAAS has now surpassed the number of approach procedures based on its ground-based predecessor, the Category-I Instrument Landing System (ILS). This is clearly a turning point for aviation and the way pilots navigate.
For the past 60 years, Category-I ILS has been used at airports throughout the National Airspace System (NAS) to guide aircraft to as low as 200 feet above the runway surface. WAAS, commissioned just five years ago, now provides this same capability, but at more runway ends. Today, WAAS LPVs can currently be found at 833 airports.
The number of WAAS LPVs will continue to grow. The FAA’s goal is to produce 500 new WAAS procedures each year until every qualified runway in the NAS has one. Additionally, WAAS has enabled a new approach capability which will be introduced in 2009.
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 and improved flight planning options enabled by WAAS.
Background
The Wide Area Augmentation System (WAAS) is a navigational system representing an enormous leap forward in air navigation. By virtue of its extensive coverage area, WAAS provides vertically-guided approach capability at thousands of airports and airstrips where this capability had previously not been affordable. It is 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 Global Positioning System (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 navigation transponders on geostationary satellites. The WAAS message improves the accuracy, availability, and safety 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, 2 master stations, 2 geosynchronous satellites, 4 uplink stations, 2 operational control centers, and the WAAS terrestrial communications network.
Benefits
Two of the FAA’s top goals are increased safety and greater capacity. 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.
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.
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.
Milestones
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.
June 2008 — The number of WAAS LPV-capable avionics passes the 35,000 mark and continues to climb steadily each month.
September 2008 — The number of runways served by WAAS LPVs surpasses the numbers of runways served by ILS.
Fonte: FAA 07/11/2008.
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