SASless
RAIM outages may occur due to an insufficient number of satellites or due to unsuitable satellite geometry which causes the error in the position solution to become too large. Loss of satellite reception and RAIM warnings may occur due to aircraft dynamics (changes in pitch or bank angle). Antenna location on the aircraft, satellite position relative to the horizon, and aircraft attitude may affect reception of one or more satellites. Since the relative positions of the satellites are constantly changing, prior experience with the airport does not guarantee reception at all times, and RAIM availability should always be checked. If RAIM is not available, another type of navigation and approach system must be used, another destination selected, or the trip delayed until RAIM is predicted to be available on arrival.
Not my quote but as in my last post I said I would have reservations about relying on GPS alone coming into an airfield with crap Wx and no alternative let down, as in the original posting of this thread
Hope this helps to show why I have my scaredy cat reservations
PS I have seen a GPS lose its signal on a flight test for an internally equipped GPS EGPWS....only once though.