report of the action team on global navigation satellite systems (gnss)

safety <strong>of</strong> life service and has been publishing <strong>the</strong> appropriate procedures for use by its aviationcustomers.177. WAAS uses a system <strong>of</strong> master stations and ground reference stations to provide <strong>the</strong>necessary augmentations to <strong>the</strong> GPS SPS navigation signal and broadcast those signals viacommunication satellites to <strong>the</strong> receivers onboard <strong>the</strong> aircraft. The initial system consists <strong>of</strong> anetwork <strong>of</strong> 2 master stations and 25 precisely surveyed ground reference stations that arestrategically positioned across <strong>the</strong> United States including Alaska, Hawaii and Puerto Rico tocollect <strong>the</strong> GPS data and transmit <strong>the</strong> information to <strong>the</strong> master stations for correction. The endstate WAAS will add communication satellites to provide dual coverage for <strong>the</strong> entire UnitedStates and additional 12 ground reference stations located in Alaska and along <strong>the</strong> nor<strong>the</strong>rn andsou<strong>the</strong>rn borders, with possible locations in Canada and Mexico.178. WAAS is designed to provide <strong>the</strong> additional accuracy, availability, continuity andintegrity necessary to enable users to rely on GPS for en-route through precision approach withvertical guidance for all qualified airports within <strong>the</strong> WAAS coverage area. This providescapability for <strong>the</strong> development <strong>of</strong> more standardised precision approaches, missed approaches,and departure guidance for approximately 4,100 runway ends and hundreds <strong>of</strong> heliports andhelipads in <strong>the</strong> United States National Airspace System (NAS).179. WAAS provides <strong>the</strong> capability for increased accuracy in position <strong>report</strong>ing, allowing formore uniform and high-quality worldwide Air Traffic Management (ATM). In addition, WAASprovides benefits beyond aviation to all modes <strong>of</strong> transportation, including maritime, highwaysand railroads. While WAAS may not provide any direct benefit to Air Traffic Control (ATC)communications, it may be an enabling technology for <strong>the</strong> future aviation data link architecture.It provides an alternative satellite-based system to maintain required levels <strong>of</strong> service in <strong>the</strong> NAS.Upon completion <strong>of</strong> <strong>the</strong> end state, WAAS will allow for <strong>the</strong> replacement <strong>of</strong> VORs, DMEs, NDBsand possibly Cat I ILS receivers with a single WAAS receiver.180. WAAS provides improved safety when operating in reduced wea<strong>the</strong>r conditions due toprecision vertical guidance on approach with 3-dimensional position guidance for all phases <strong>of</strong>flight. WAAS provides an inexpensive, instrument flight rules (IFR) area navigation system withglobal coverage, leading to: greater runway availability, reduced separation, more direct flightpaths, new precision approach services and reduced disruptions (delays, diversions orcancellations).181. There are also significant benefits to be realised by <strong>the</strong> FAA due to <strong>the</strong> reduction inmaintenance and replacement costs associated with some older, expensive ground-basednavigation aids to include NDBs, VORs and DMEs. FAA has commissioned WAAS on 10 July2003.4. GAGAN182. The Indian Space Based Augmentation System (SBAS), called GAGAN (GPS And GeoAugmented Navigation), is being implemented by <strong>the</strong> Indian Space Research Organisation(ISRO) in collaboration with <strong>the</strong> Airports Authority <strong>of</strong> India (AAI) over <strong>the</strong> Indian airspace, forcivilian aircraft navigation. The GAGAN system is expected to bridge <strong>the</strong> gap between <strong>the</strong>evolving European EGNOS system and <strong>the</strong> Japanese MSAS system. The GAGAN system willfollow <strong>the</strong> recommendations <strong>of</strong> <strong>the</strong> Asia Pacific Air Navigation Plan for ICAO Regional Group(APANPIRG) as per <strong>the</strong> ICAO SARPs.34