Since RAIM is presumably still required for a TSO146 GPS, is it sensible to file an alternate which is also GPS-only?
The above is for
US airspace only of course... in European airways an N-reg has to carry all the old kit anyway
plus whatever the FAA requires for "IFR".
Incidentally there are various nooks and crannies with IFR GPS receivers on
European-made planes which have been moved to N. These would not normally have an FAA approved GPS supplement in their flight manual; one has to get this organised through an FAA office and it is a right messy job. The Heathrow FAA office reportedly doesn't want to do it. The European manufacturers normally sort this out on their US sales via their US dealer who gets a custom supplement done out there. Very few European pilots of N-reg have bothered with this, relying instead on the unit being BRNAV approved on the original type certificate, which is good enough for Europe IFR enroute. But it would not be legal flying IFR in US airspace.
The above para is relevant if flying the new GPS approaches, of which there are a number around Europe (not UK yet). An N-reg may well need the custom supplement to fly these. A G-reg needs one too and in that case it is an EASA Major Mod which is something else ........... luckily there isn't (
AFAIK) a GPS approach in Europe yet without a conventional (usually an ILS) alternative (see LKPR for example). This is a very grey area.