Challenging EGNOS on the LPV 200 Vertical Accuracy Tail Requirements

F. Bauer, E. Tapias, C. López de Echazarreta

Abstract:	The European Geostationary Navigation Overlay Service (EGNOS) is the first pan-European SBAS satellite navigation system. It augments the US Global Positioning System (GPS) and makes it suitable for safety critical applications such as flying aircrafts or navigating ships. Consisting of two geostationary satellites and a network of ground stations, EGNOS achieves its aim by transmitting GPS-like navigation signals containing integrity and differential correction information applicable to the navigation signals of the GPS satellites. EGNOS correction data improves the accuracy of the current GPS services from about 10 m to about 2 m for users in Europe and beyond. The EGNOS Safety of Live service has been officially declared available for aviation the 2nd March 2011. Space-based navigation signals have become usable for the safety-critical task of guiding aircraft - vertically as well as horizontally - during landing approaches. EGNOS currently offers the following services for aeronautical users: • En Route / Non Precision Approach (LNAV), • APV-1 approach conditions (LPV) Localizer Performance with Vertical guidance (LPV) are the highest precision GPS (EGNOS enabled) aviation instrument approach procedures currently available without specialized aircrew training requirements, such as Required Navigation Performance (RNP). Landing minima are usually similar to those in an Instrument Landing System (ILS), that is, a Decision Height of 200 feet (61 m) and visibility of 1/2 mile. LPV 200 service (Instrument Landing approach with Decision Height of 200 feet, CAT-I like approach capability) was not part of the original EGNOS capabilities. It has been recently introduced as part of an evolution of the EGNOS mission on a new EGNOS System release currently under qualification. LPV 200 service induces new constraints: • More stringent Vertical Alarm Limit: 35m • More stringent Vertical Accuracy requirement: o 4 meters at 95%. o 10 meters at 1E-7 per approach in Fault-Free conditions o 15 meters at 1E-5 per approach in degraded conditions (so-called Effective Monitoring Threshold (EMT) according to ICAO SARPS). For the first time, EGNOS faces these stringent requirements on the accuracy distribution tail of the user vertical position error (VNSE) which are usually reserved to integrity and continuity performances. This paper describes the methodology that has been carried out to understand, endorse and qualify EGNOS in front of the new LPV 200 requirements on the accuracy distribution tails for the fault-free and degraded conditions. It also presents preliminary performance results of the User Vertical Accuracy within the European Civil Aviation Conference (ECAC) service area that have been derived through simulations of synthetic scenarios with different ionosphere dynamics, and also using a real data collection campaign from a given network of receivers spread out along the service area.
Published in:	Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014) September 8 - 12, 2014 Tampa Convention Center Tampa, Florida
Pages:	3277 - 3288
Cite this article:	Bauer, F., Tapias, E., de Echazarreta, C. López, "Challenging EGNOS on the LPV 200 Vertical Accuracy Tail Requirements," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 3277-3288.
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