GNSS Library

A. WAAS implementation and WAAS equipage will allow the NAS routes to be restructured, resulting in shorter flight times, saving aircraft operating time and passenger time. In a study commissioned by the FAA's Air Traffic Organization and sponsored by the GPS Product Team titled, New England GPS Alternate Route Study, the average reduction in flight time for the routes analyzed was one (1) minute. Savings due to universal WAAS equipage were further analyzed through an Air Traffic study, The Southern Region Multi-Center Study. This one-minute value was used to calculate benefits attributed to WAAS as a result of restructuring NAS routes. For the lower bound of the benefits to cost ratio the assumption was made that only 30% of all flights would recognize this benefit. This figure was used because it is recognized that some aircraft already have direct route capability. The benefit calculations for savings from reduced flight times begin in 2006, when it is anticipated overall equipage is great enough to begin flying the new routes. The benefits for reduced flight times are only those that will be attributed to future restructured NAS routes.   

A. GPS is an essential element of the future navigation architecture. Existing ground-based navigation aids have limited coverage due to terrain, and the majority of instrument approaches do not have vertical guidance due to the cost of siting and operating an Instrument Landing System (ILS). A satellite-based navigation system is needed that can provide global coverage, regardless of user altitude, and support precision approach operations at every runway without the need for costly ground infrastructure. Note that providing vertical guidance on an approach reduces the risk of controlled flight into terrain (CFIT) significantly. This satellite-based navigation system must also be global, so that the level of safety can be raised not only within the U.S. but also in the rest of the world.

Without augmentation, GPS is already used as a supplemental means of navigation, in addition to conventional ground-based navigation. Augmented by the Wide Area Augmentation System (WAAS), satellite navigation will provide en route, terminal area, and approach services, down to GLS precision approach. Augmented by the Local Area Augmentation System (LAAS), satellite navigation will serve all categories of precision approach.

A second civil frequency is the next logical step in modernization of the navigation architecture and providing improved satellite navigation services. Within the U.S., it will improve the reliability of satellite navigation, particularly against the potential threats of interference and ionosphere. Outside of the U.S., it will make precision approaches possible with even less infrastructure than is achievable with WAAS alone. In addition, additional operational benefits will be defined as the service is defined and applications for that service are developed.   

A. When the final WAAS architecture is in place, users in the NAS will be able to use GPS/WAAS as a stand-alone navigation aid for en route through GLS precision approach operations. Like WAAS, LAAS relies on GPS for basic navigation signals. LAAS will operate independently from WAAS, while at the same time complementing WAAS by providing additional GPS augmentation to support airport requirements for CAT-II/III precision approach operations. LAAS will also provide a GLS capability at locations where WAAS cannot, as well as provide a signal, which could be used, for surface navigation in the terminal area.   

Most dealers provide a package price when they sell a receiver. This package includes installation and airworthiness inspection, as well as the actual equipment. These packages can range anywhere from approximately $3,000 (US) for a basic general aviation IFR GPS receiver installation/certification, to $10,000 (US) for a more sophisticated GPS receiver installation/certification on a commercial aircraft. When comparing prices of GPS avionics versus existing ground-based avionics, one must consider that one GPS receiver will eventually replace all avionics associated with these other ground navigation aids (VOR/DME, NDB, Category I ILS).   

A. The NAS currently provides several systems to support enroute and terminal area navigation, including non-precision approach. These include VOR with associated DME, TACAN, NDB, Loran-C, and GPS.

The operational benefits of GPS/WAAS, especially increased routing flexibility and many more precision approaches, will motivate most operators of aircraft used extensively for IFR operations to equip with GPS/WAAS in the five to six year period following the availability of services. At that point, the current ground based systems - VOR, DME, and ILS - will become back-up systems for these operators. Since most aircraft will be navigating using GPS/WAAS, substantial reductions can then be made in the number of VOR/DME and ILS ground facilities. Maintaining the current VOR/DME system is expensive, thus, there is a considerable financial incentive to reduce the number of VOR/DME. As soon as GPS/WAAS avionics are available, operators are anticipated to begin equipping with it to achieve the associated operational benefits and convenience.