Anthony
Quote"There's also too much willingness to trust GPS for approaches (in theory or in practice), as a substitute for ILS. But ordinary GPS cannot come close to ILS for accuracy, especially for precision approaches. Using GPS in place of ILS requires LAAS (which is not GPS at all, but merely a supplementary technology), and even that is delicate. And no, things like WAAS or RAIM do not make GPS anywhere close to foolproof."
Not totally true. In the USA there are now more LPV approaches than ILS approaches. LPV approaches use WAAS technology to give ILS like indications in the cockpit to help you fly down to CAT I limits. They currently go down to 200 feet and 1/2 mile RVR (Depending on the runway / approach lighting).
WAAS is a form of SBAS (Satelite Based Augmentation System). The Australians are leading the way with GBAS (Ground Based Augmentation System)at airports such as Sydney. GBAS is a much improved form of LAAS which never really got fully developed.