Satnav News, Fall 2017
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FAA Navigation Programs AJM-32 http://gps.faa.gov SatNav Past, Present, and Future The WAAS Prediction Tool Extends WAAS Analysis to Forecast Future Performance Since the FAA commissioned WAAS into GPS/RNAV approach charts. Even though service in July 2003, the WAAS Test Team at the procedures are published per runway, the the William J. Hughes Technical Center has prediction tool assumes that WAAS availability reported real time and historical performance is the same for an entire airport. of the system. The latest objective, however, is to demonstrate WAAS performance in the The predicted WAAS service is available to future. To meet this goal, the WAAS Test the public on the internet. The results shown Team developed a tool to predict future WAAS on the website are actually the combination of performance. two tools. The first is the baseline prediction tool. This tool relies on the daily repeatability The WAAS prediction tool forecasts WAAS of the GPS constellation. Since the GPS availability for each airport that has published constellation is repeatable day to day, WAAS Lateral Precision (LP) and Lateral Precision performance is also repeatable. This baseline with Vertical Guidance (LPV) procedures. prediction tool accounts for predicted WAAS The FAA has published over 4,500 LP and performance for the vast majority of the time. LPV instrument approach procedures in the The second tool is the geometric prediction United States. These published procedures tool. The geometric tool simulates the WAAS are shown on the LPV or LP line of minima on algorithms. The website shows the results News Figure 1. WAAS Predicted Airport Availability for November 29, 2017 SatNav News Volume 62 Fall 2017 Figure 2. San Francisco Airport (SFO) Predicted Outage on November 29, 2017 from the geometric tool when there is a change for Runway 28L beginning at 10:03:12 GMT in the configuration of WAAS. For example, and lasting for 870 seconds. a change in configuration could be a GPS satellite unavailable due to maintenance or a The WAAS Test Team continuously validates the WAAS reference station is taken out of service prediction tool. The validation is documented for an upgrade. For the end user, whether the in a monthly report. As a first step in the prediction came from the baseline tool or the early development of the tool, the WAAS Test geometric tool is transparent. Team determined the accuracy of the tool’s predictions after an event occurred. That is, if When visiting the website (http://www.nstb. there was a planned GPS satellite outage, the tc.faa.gov/AirportSchedules/) the user is tool would be run after that outage occurred shown a familiar, interactive Google Maps with the exact times that the GPS satellite was display. The user is presented with the not available. This approach provided a view predicted WAAS performance at airports for of how well the prediction tool matched actual a user specified date. The date is entered performance. by the user in the upper left corner of the display. A user can also view results for a The method to validate is different for the selected airport by using the search bar at baseline tool and the geometric tool. The the top of the display. For example, Figure baseline tool can only be validated during 1 shows the predicted WAAS availability on steady state conditions. A baseline day is November 29, 2017. The boxes in the figure established when the actual performance of depict airports with a GPS/RNAV LPV or LP WAAS is consistent over a time period or there published approach. The blue boxes mean are no changes in the WAAS configuration no outages are predicted and yellow boxes or GPS satellite maintenance actions. mean at least one outage is predicted for that The baseline day represents the WAAS airport. A user can click on one of these boxes performance most of the time. The geometric to get more information. Figure 2 illustrates tool, however, calculates WAAS performance the pop up window that appears when San when there is a change in the system. The Francisco Airport (SFO) is selected. The text in WAAS algorithms are modeled in this tool. the window shows there is a predicted outage The geometric tool, therefore, is most useful SatNav News Volume 62 Fall 2017 2 Figure 3. SFO Prediction Statistics for November 29, 2017 during these occurrences of disrupted WAAS tool’s performance. This type of validation is configuration. Both tools are checked against reported for each outage, either predicted or actual performance to determine the accuracy actual. of the prediction. Predicting WAAS performance is utilized In using the above example, the accuracy in several ways. FAA WAAS operations of the WAAS prediction for November 29 is uses the prediction results to assist in evaluated. Figure 3 shows how well the tool planning maintenance and upgrades to predicted actual WAAS performance at SFO. WAAS. Also, the WAAS Test Team uses to tool The top part of the figure shows the times for to better understand how changes in WAAS the predicted and the actual outage. Below configuration affects WAAS performance. In that are the prediction statistics for SFO on the future the WAAS prediction tool may be November 29. From the stats, the predicted used to generate Notices to Airmen (NOTAM) outage at SFO started 30 seconds after to alert users of reduced WAAS availability. the actual outage occurred. Also, the end of the predicted outage was 60 seconds The WAAS prediction tool continues to be after the actual outage. That 90 second refined. Regular examination of the accuracy discrepancy between the predicted and actual of the tool assists in keeping the tool robust. outages resulted in about 0.1% of time that Moving forward, the WAAS prediction tool will WAAS performance at SFO was incorrectly have many uses in support of WAAS service. predicted at SFO on this day. Prediction - Bill Wanner, FAA ANG/WJHTC accuracy of 99.9% or better is typical of the SatNav News Volume 62 Fall 2017 3 European airlines grow appetite for EGNOS Reprint from Airliner World, October 2017 European airlines are quickly upgrading their fleets to catch up with the rapid proliferation of the so called LPV approach procedures (Localizer Performance with Vertical guidance), which are now available at 214 airports across Europe as of August 2017. Since the EGNOS Safety of Life service declaration in 2011, an increasing number of procedures, which today account for a total of 371, has been relying on this technology to provide alternative means to ILS CAT-I approaches. Contrary to ILS, LPVs do not rely on any ground infrastructure at the aerodrome, which constitutes a significant advantage to medium size airports that cannot afford the installation or maintenance of these landing systems. LPVs Beside these voluntary ANSP initiatives, the represent also a great backup during ILS PBN Implementation in the European Air disruptions and a cost effective solution for Traffic Management Network regulation to secondary runway ends which are not served be released by EC in the coming months, by precision approaches. complementing the Pilot Common Project (PCP), will request the publication of LPV For these and other reasons, the implementation procedures to all instrument runway ends not plans announced by the different European served by a precision approach by (tentatively) national air navigation service providers 2020, and to those served by precision (ANSPs) estimate a total of nearly a thousand approaches by 2024. LPV procedures (APV-I and LPV200) by the 1 end of 2020 (see map ). By then, according to Given this steep trend in LPV publications, the a recent study by ESSP (the EGNOS Service upcoming regulation and the ILS rationalisation Provider), 78% of all IATA flights in Europe plans, like that already announced by France will land at destinations with EGNOS-based (30 ILSs removed to date), European operators procedures. SatNav News Volume 62 Fall 2017 4 are now taking into serious consideration this Amongst business operators, whose fleets technology that is finally becoming available show higher penetration of EGNOS-ready at their network of destinations. boxes than commercial airlines, the following are already benefiting from the use of these This interest is reflected in the way airlines are procedures: Air Alsie, AstonJet, CAT Aviation, increasingly ordering LPV (SBAS) functionality Flying Group, GlobeAir, International Jet options for their new deliveries (forward- Management, iXAir, Jet Aviation Business Jets, fits) - by means of Service Bulletins - or are NetJets Europe, Speedwings Executive Jets, upgrading their existing non-SBAS-capable TAG Aviation and VistaJet Ltd. aircraft by means of Supplemental Type Certificates (retrofits). The operators’ demand of LPV capabilities has urged aircraft manufacturers to offer Some of the pioneer European commercial solutions for both new and legacy aircraft. airlines making use of LPVs on their daily While some manufacturers are offering SBAS operations are AirBaltic, Air Transport by default on the flagship models as it is the International, Aurigny Air Services, case for Bombardier CSeries, others offer it Hebrideanair, International Jet Management through Service Bulletin options (forward-fit) and Swiss International Airlines. that can be activated prior to the delivery of the aircraft or while in service. This is the case, for Work is in progress for many other airlines, instance, of Airbus A350, ATR 42-600 and 72- such as AirNostrum, CityJet, Croatia Airlines, 600, Bombardier CRJ, Twin Otter and Dash-8 EasyJet, Eastern Airways, Finnair, HOP!, families or Embraer E-Jet and ERJ models. Loganair¸ Skybus, NextJet and Widerøe, who are either waiting for the delivery of their Additionally, operators have the chance to SBAS capable orders, or in the process of upgrade their fleets via Supplemental Type certification of their existing fleets, or training Certificates that can be installed by MROs.