In my experience where there is an ILS approach there is also an RNAV approach for the same runway.
Flying an ILS with the GPS175
Doesn't mean they are identical, that is for sure.
My understanding is that the OP @TBalch was asking about coupling the GPS 175 with their KAP 140 autopilot for an ILS approach. The answer is that it's allowed for the approach legs before the FAF and for the missed approach leg, but you can't have it coupled to a GPS at and inside the FAF; you need either to couple it to a nav radio, or to hand fly the section from the FAF to DH.I’m re-reading my post to see where I wrote that the approaches are identical. They are not, but the RNAV approach will get you into the same runway. If you have ILS equipment, get out the ILS plate. If you have a panel navigator, get out the RNAV plate.