GNSS Performance Limitations over Airports at High Latitude and in the Geo Signals Overlapping Zones

D. Belloni, C. Carnebianca, F. Costa, G. Nobile, A. Parente and R. Rauber

Abstract:	As well known, the Initial Operational Capability (IOC) of the Global Navigation Satellite System GNSS, consisting of satellite and ground based augmentation systems (SBAS/GBAS), shall rely on a reduced set of geo-stationary satellites with respect to that required by a full operational system. The SBASs under implementation, such as WAAS, EGNOS and MSAS, constitute Regional Augmentation Systems (RASs). According to ICAO recommendations, the geo-overlay signals among the RASs shall be interoperable to support the seamless GNSS concept. However, this feature is under assessment and a seamless solution is not ready yet. In this perspective, aeronautical users in terminal phases of flight during high bank turning manoeuvres may experience service performance limitations, due to the following conditions: a) complete loss of the geo-overlay signals, especially at high latitude airports b) need to switch to a geo-signal pertaining to another regional area The major objective of this paper is the attempt to: - Analyse and characterize the potential operational limitations - Verify to what extent conventional flight procedures in the above scenario can be considered compatible for operations with a GNSS as “primary” or “back-up” means - Find criteria to ease full compatibility achievement. The study cases over selected airports have been carried out with SAPET (SAtnav Performance Evaluation Tool), a resource of AIRNAS (Air Navigation and Airport System) designed for operational instrument flight procedure design, validation and maintenance. The results show that for high latitude airports, loss of geo-signals (depending on the antenna mask angle gain pattern) may be experienced during high bank manoeuvres (typically at altitudes above 3000 ft.) and it can be translated into aircraft heading-bank angles restrictions with consequent operational limitations. For the overlapping zones, the need to switch to interoperable geo-overlay signals, in case of lack of full geo-overlay signals interoperability, may be considered as complete loss of the geo-overlay signals leading to aircraft headingbank angles restriction as well. Such restrictions could be, to a certain extent, mitigated if the optical mask of the aircraft (instead of the local horizon) would be considered, but they still persist. Further improvement could be attained by redesigning the turning manoeuvres (when practicable) to overcome or mitigate the identified limitation. However, from operational viewpoint, it should be investigated the impact of few seconds of high bank turning manoeuvres ( that may lead to a few seconds of service outage) on the flight safety.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	567 - 574
Cite this article:	Belloni, D., Carnebianca, C., Costa, F., Nobile, G., Parente, A., Rauber, R., "GNSS Performance Limitations over Airports at High Latitude and in the Geo Signals Overlapping Zones," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 567-574.
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