Pilot Pete,
GNSS = Global Navigation Satellite System such as the American
GPS and the Russian GLONASS. Latest news on the on/off European Galileo system is that it's finally on but we don't know when yet.
EGNOS = European Geostationary Navigation Overlay System. An overlay that improves the accuracy of any of the geostationary satellite systems, enabling their use for Precision Area Navigation (PRNAV) In trials completed at Nice airport in September last year, EGNOS consistently provided precision guidance (within 30m horizontal and 40m vertical) on two complex fixed radius turns over 20nm to establish on a 2nm straight in final approach.
The concern over traffic congestion will eventually force the use of area navigation and precision curved approaches beyond the capability of micro-wave systems. Radio beacons have served us well but the days of aircraft streaming in long straight lines between radio stations cannot continue. There simply isn't enough room any more.
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Through difficulties to the cinema