Modelling of EGNOS Navigation System Errors for Cat I Autoland

C. Milner, C. Macabiau, A. Gantelet, S. Prakasen, N. Tairo C. Manase, L. Azoulai, F. Tranchet

Peer Reviewed

Abstract:	Implementations of the Satellite Based Augmentation System (SBAS) concept are providing the capability to perform Localizer Performance with Vertical (LPV) operations in continental U.S (CONUS) and European airspace down to 200ft minima, equivalent to Cat I minima. Enabling autoland with LPV operations is a solution to enhance safety by reducing flight crew workload and fatigue, especially in adverse conditions. Airbus and ENAC provide in this paper a SBAS Navigation System Error model to be used for demonstration of autoland capability with LPV-200 operations under Cat I conditions. Similarly to the GBAS Autoland certification, autoland demonstration must be statistical so as to demonstrate through simulation that aircraft is landing safely within the touchdown box. To support this demonstration, a SBAS NSE model is required. This paper presents the end-to-end developments of the SBAS NSE model as well as the methodology that has been applied to develop it, relying on EGNOS data from 2014 and 2020. The NSE model is developed in three phases. In the first phase, the residual ranging errors following SBAS (EGNOS in the case studied) corrections are modelled. This relates to the corrected Signal-In-Space errors (orbit, clock, nominal signal and antenna biases) as well as the corrected ionospheric errors. The tropospheric and airborne (multipath and noise) residual errors are modelled using [DO-229, 2020] models The second phase uses the residual range error models obtained, with knowledge of the satellite geometry (almanac), in order to determine the position domain performance. In the final phase, Gaussian error generation is used to obtain a single model for each user averaging over time the outputs from phase two. The output of phase three is then a distribution of navigation system errors (NSE) both horizontally and vertically, to be used in Airbus Autoland simulations. It is observed for the 2014 processing, 2014 being the solar maximum of the current solar cycle, that in the central ECAC region the Autoland nominal case requirements are met whilst performance is limit at the corners of ECAC. Processing for 2020 data, which benefits of EGNOS performance improvements as well as a lower solar activity compared to 2014, enable to define a SBAS NSE model that is expected to meet the autoland average risk and limit risk. In the future, SBAS coverage extension enabled by systems such as EGNOS v3 will further extend the benefit of having autoland capability with LPV-200 operations.
Published in:	Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022) September 19 - 23, 2022 Hyatt Regency Denver Denver, Colorado
Pages:	1496 - 1513
Cite this article:	Milner, C., Macabiau, C., Gantelet, A., Prakasen, S., Manase, N. Tairo C., Azoulai, L., Tranchet, F., "Modelling of EGNOS Navigation System Errors for Cat I Autoland," Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), Denver, Colorado, September 2022, pp. 1496-1513. https://doi.org/10.33012/2022.18422
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