GNSS Library
GNSS Library - Fact Sheets This area of the Library contains downloadable fact sheets on various FAA satellite navigation initiatives. GPS The technology behind GPS is relatively simple. A constellation of 24 satellites orbiting 11,000 miles above the earth emits signals to receivers on earth. By measuring the travel time of a signal transmitted from each satellite, a receiver can calculate its distance from that satellite. Satellite positions are used by a receiver as precise reference points to determine the location of the receiver. When receiving the signals from at least four satellites, a GPS receiver can determine latitude, longitude, altitude, and time. In 1989 the Department of Defense (DoD) launched the first production series of GPS satellites. This effort was the initial step in revolutionizing the way we find our location on earth. The 24 satellite system was declared operational by the DoD on December 8, 1993. A similar declaration was made by the Federal Aviation Administration (FAA) in February 1994 regarding the civil operational status of GPS. The overall objective of the FAA is to support the operational use of satellite navigation for all civil aviation needs including departure operations, terminal, oceanic, en route, non-precision and precision approaches, auto-landing, and surface navigation. Some of the incremental steps to achieve this goal have already occurred, many are currently underway, and more are planned for the near future. The international community can expect many benefits from satellite navigation (GPS and its augmentations) including:
Additionally, the FAA is striving to enhance existing relations with other civil aviation authorities and appropriate organizations to create a seamless, worldwide satellite-based navigation system. Such a system will permit the use of a single piece of equipment to support aviation navigation on a global basis. Furthermore, it will provide the foundation for future communications, navigation, and surveillance systems and increase safety for carriers and passengers internationally. In furtherance of international acceptance of GPS, on March 29, 1996, the President of the United States officially reiterated the U.S. commitment to continue the broadcast of GPS signals on a worldwide basis free of charges for the foreseeable future. The President also made a promise to discontinue the use of selective availability (SA) by the year 2006. In January 1999, as a direct result of the benefits brought about by GPS, Vice President Gore announced that the U.S. would begin a GPS modernization to further extend the systems capability. This modernization would include two additional GPS signals to enhance the civilian and commercial service. On May 1, 2000 the President announced that effective immediately, the use of SA would be discontinued. This will result in accuracies up to ten times more accurate than previously possible. All users worldwide will benefit from these commitments. Although GPS and its augmentations can provide major benefits for navigation, especially for the civil aviation community, there are many steps that must be taken to implement this technology. Standards and procedures development, facility preparation, training, international cooperation, and many other activities play a critical role in bringing these systems into operational use. Based on the capability of GPS, the FAA has charted a course for the future and is working to build a new navigation capability--one that will guide our Nation's Airspace System into the 21st century. For futher information regarding GPS, please contact: WAAS WAAS is an extremely accurate navigation system developed for civil aviation. Before WAAS, the U.S. National Airspace System (NAS) did not have the potential to provide horizontal and vertical navigation for approach operations for all users at all locations. With WAAS, this capability is a reality. WAAS provides service for all classes of aircraft in all phases of flight - including en route navigation, airport departures, and airport arrivals. This includes vertically-guided landing approaches in instrument meteorological conditions at all qualified locations throughout the NAS. WAAS uses a network of precisely-located ground reference stations that monitor Global Positioning System (GPS) satellite signals. These stations are located throughout the continental United States , Hawaii , Puerto Rico and Alaska ; with additional stations being installed in Alaska , Canada and Mexico . These stations collect and process GPS information and send this 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 (GEO) satellites. The WAAS message improves the accuracy, availability, and integrity (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. Availability is increased through the addition of the WAAS satellites providing additional course correction. WAAS also eliminates the requirement to conduct receiver autonomous integrity monitoring (RAIM) predictions. In terms of safety, WAAS provides pilot alerting within 6 to 8 seconds (depending on the airborne equipment) anytime the input signal for positioning becomes unusable. WAAS reached initial operational capability for aviation use in the NAS on July 10, 2003 , providing navigation throughout the entire NAS and vertically-guided approach service known as localizer performance with vertical guidance (LPV) to the 48 contiguous states. Initially, LPV capability enabled pilots using WAAS to descend with stabilized vertical guidance to decision altitudes as low as 250 feet above the runway and visibility minimums as low as ½ mile at qualified runways. In March 2006, the FAA announced the extension of this initial capability to decision altitudes as low as 200 feet above the runway. Since our first service delivery in 2003, our focus has shifted to expand LPV performance to all areas of the continental United States , most of Alaska , and most of Canada and Mexico . This expansion will be complete in 2008. The implementation of WAAS into the NAS will result in safety and capacity improvements. WAAS-enabled procedures can open more usable airspace to pilots and provide more direct routing. WAAS will also eventually reduce operations costs for the FAA by enabling the removal of a portion of existing ground-based navigation infrastructure. WAAS is an enabler of Required Navigation Performance (RNP); a critical component of the movement toward performance-based navigation in the NAS. RNP is a concept of area navigation (RNAV) operations in which the aircraft navigation system provides containment, monitoring, and alerting for flight within a given airspace. WAAS navigation services meet or exceed the most stringent RNP performance values. As air traffic management becomes more global, the WAAS concept is being applied to civil aviation infrastructure worldwide, enabling global safety improvements. WAAS is the first of several space-based augmentation systems being developed throughout the world and is compatible with all other international satellite-based augmentation systems. Moreover, with more stringent RNP standards, inefficiencies in airspace utilization could be reduced, thus increasing traffic flows and reducing delays. 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 24, 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. The next phase of WAAS is referred to as the Global Navigation Satellite System Landing System (GLS) segment. The GLS phase of WAAS is scheduled to coincide with the operational capability of GPS modernization and is scheduled to be completed in 2013. GLS will utilize, and depend upon, improvements that the Department of Defense (DoD) will make as part of its GPS modernization program. GPS modernization will enable WAAS to provide the GLS capability during periods of severe solar storm activity and provide additional security against interference to the GPS. WAAS is the first of many augmentation systems being developed throughout the world. In the future, WAAS will be compatible with international satellite-based augmentation systems, enabling WAAS-type augmentations worldwide. Download WAAS Fact Sheet in PDF format. LAAS - The FAA’s Future GPS Approach and Landing System The Local Area Augmentation System (LAAS) will augment the Global Positioning System (GPS) to provide an all-weather approach and landing navigation capability. LAAS will provide precision approach service within a nominal 23-mile coverage volume around the airport where the ground system is installed and broadcasts differential GPS corrections and integrity messages via a very high frequency (VHF) radio data link. LAAS will meet high accuracy and availability performance requirements necessary for Category I, II, and III precision approach operations. LAAS is expected to provide improved service over the Instrument Landing System (ILS) and reduced operating costs. LAAS Benefits - Precision approach capabilities to all runways at an airport from a single LAAS ground facility, reducing the need for costly redundant infrastructure - Reduced taxi time by elimination of ILS critical areas - Precise positioning information of aircraft that can be used by surface surveillance systems to prevent runway incursions during low visibility conditions - Curved and segmented approach paths, not possible using current instrument landing systems, for Category I, II, and III precision approaches Next Steps for LAAS LAAS remains a research & development project focusing on the resolution of outstanding integrity and safety issues to reduce risk for future development. The FAA Ground Based Augmentation System (GBAS) Office is implementing a provably safe design at a prototype LAAS facility in Memphis , TN. This task is being performed under contract with Honeywell. By September 2006, the integrity analysis and integrated prototype system will be completed. Validation testing will follow. The FAA is also working with other service providers to facilitate development of an International Civil Aviation Organization (ICAO) Standards and Recommended Practices (SARPs) compliant Category I LAAS, based on the Memphis prototype by 2008. International Standards for LAAS The FAA shares the international goal of a worldwide, seamless, interoperable Global Navigation Satellite System (GNSS) - RTCA has published the LAAS Minimum Aviation System Performance Standards (MASPS). This document allocated overall LAAS requirements between the ground equipment and the avionics (September 28, 1998) - The development efforts of the avionics have been captured in
the LAAS Minimum - ICAO’s Navigation System Panel (NSP), formerly the Global Navigation Satellite System Panel (GNSS-P), has developed the SARPs for the GBAS for Category I (November 1, 2001) |
