If being vectored to the FAF I wouldn’t worry about coupling. But when you have to fly the complete approach including a course reversal the having the autopilot fly the whole approach coupled vertically and laterally would seem pretty useful
Fortunately, all G3X/G3X Touch systems
will fly a complete coupled approach including a course reversal with little or no pilot action after activating the approach.
Since you are from Salem, let's look at the RNAV 31 approach at McNary Field (KSLE) as an example.
Since you want to fly a procedure turn in this example, we will approach the field from the NW and use the ARTTY transition. We will enter the approach at ARTTY at 3,000' MSL and not need to manually make any additional altitude or other changes before reaching the runway.
At this point in the approach we are in altitude hold at 3,000' inbound before ARTTY. The approach is loaded and activated, the APR button has been pushed on the GMC to arm for approach (GP) capture, and the baro minimum for the LPV approach has been selected. Even though the full procedure turn and approach/descent are ahead of us, we are done making ANY changes until we hear the "Minimums, Minimums" aural annunciation at the bottom of the glidepath and either land or go missed (by pressing a single TO/GA button).
In this example we have passed the ARTTY transition, and are 17 nm outside of the NECIP IAF where we start the procedure turn. Again, nothing to do but monitor the flight.
Here we have passed NECIP outbound and are completing the procedure turn.
As we approach the NECIP IAF inbound, you can see that the vertical deviation bar is not yet present on the PFD.
After crossing the IAF, the vertical deviation bar is present on the PFD and we are well below the glidepath as the glidepath crosses NECIP at 4,000' MSL.
Finally, we capture the glidepath several nm ahead of the FAF at our present altitude and begin the descent. No descent is ever needed at the waypoint before the FAF (AFAIK). You just maintain the published altitude for the FAF-1 waypoint, and fly straight into the glidepath.
At the bottom of the glidepath, you can see the baro min indicator rising in the altitude tape.
A tip for flying the missed approach. At ANY time during the above procedure, once you are established in ALT hold at 3,000', you can change the selected altitude to 3,700' in preparation for flying the missed approach. If you go missed, just add power and press the TO/GA button which transitions both the G3X system and the Garmin navigator to fly the missed to the ARTTY hold at 3,700'. The autopilot will automatically couple to the missed approach procedure, climb to 3,700', and enter the hold at ARTTY. It will stay in this hold until you give it directions to do otherwise.
While it seems that many, if not most, RNAV approaches do not have intermediate fixes that require step down(s) between the IAF and the waypoint before the FAF, there are some that do. In those cases these step downs can be handled by either using GTN VNAV, or simply using the altitude select and VS mode when instructed by ATC. As Bill mentions above, in the real world of flying IFR with ATC instructions, it is often the case that it is simpler to just manually manage the altitude changes when cleared to do so.
BTW, if it were up to me, I would show the profile for this approach in this manner to make it clear that when arriving at NECIP at 3,000', you can fly level from this point to intercept the glidepath.
Steve