Concerns over the accuracy, availability, integrity and
continuity of Global Navigation Satellite Systems (GNSS)
have limited the integration of GPS and GLONASS for
safety-critical applications. More recent augmentation
systems, such as the European Geostationary Navigation
Overlay Service (EGNOS) and the North American Wide
Area Augmentation System (WAAS) have begun to address
these concerns. Augmentation architectures build on the
existing GPS/GLONASS infrastructures to support locationbased services in Safety of Life (SoL) applications. Much of the technical development has been directed by air traffic management requirements, in anticipation of the more extensive support to be offered by GPS III and Galileo. WAAS has already been approved to provide vertical guidance against ICAO safety performance criteria for aviation applications. During the next twelve months, we will see the full certification of EGNOS for SoL applications.
This paper identifies strong similarities between the safety
assessment techniques used in Europe and North America.
Both have relied on hazard analysis techniques to derive
estimates of the Probability of Hazardously Misleading
Information (PHMI). Later sections identify significant
differences between the approaches adopted in application
development. Integrated fault trees have been developed by
regulatory and commercial organisations to consider both
infrastructure hazards and their impact on non-precision
RNAV/VNAV approaches using WAAS. In contrast,
EUROCONTROL and the European Space Agency have
developed a more modular approach to safety-case
development for EGNOS. It remains to be seen whether the
European or North American strategy offers the greatest
support as satellite based augmentation systems are used
within a growing range of SoL applications from railway
signalling through to Unmanned Airborne Systems. The key
contribution of this paper is to focus attention on the safety
arguments that might support this wider class of location
based services
