The ILS approach remains the "go to" approach after all these years. (First tested in 1929 and installed operationally in 1941.) Refer to Procedures & Techniques / Instrument Landing System for background information about:
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
If you have ASC 007 you are a Category C airplane unless you have a maintenance logbook entry raising your maximum landing weight. If you do not have ASC 007, you are a Category D airplane, end of discussion. See G450 Procedures & Techniques / Approach Category for an explanation.
Photo: From Eddie's cockpit.
Figure: Arrival Page, from G450 Aircraft Operating Manual § 2B-27-00, figure 37.
Approach selection is made either through the MCDU (NAV > ARRIVAL) or the NAV display.
Photo: From Eddie's cockpit.
There is an advantage to making this selection on the NAV display: if the appropriate chart is selected in green from the CHARTS page, future changes to the approach on the NAV display will automatically change the selected chart.
[G450 Aircraft Operating Manual §2B-05-50 2.A. (2)]
Alternatively, you can preset the localizer frequency and the approach back course. (This would be advisable if you expect to be on a complicated STAR with short vectors to ILS final, precluding the auto-tune function.) You would enter the ILS identifier into appropriate LSK in the PROGRESS page and the ILS approach course in the Display Controller PREVIEW submenu.
Figure: LNAV Mode Selection, from G450 Aircraft Operating Manual, §2B-08-00, Pg. 7.
The book isn't very clear about this, but it is a basic function we've been doing for as long as we've had flight directors: use LNAV only for localizer only, APPR for an ILS.
Figure: APR (Approach) Button, from G450 Aircraft Operating Manual, §2B-08-00, Pg. 11.
Pressing APR on the localizer/glide slope approach arms the glide slope and allows capture, ignoring the altitude select window.
Figure: ILS Approach Mode, from G450 Aircraft Operating Manual, §2B-08-00, Figure 30.
[G450 Aircraft Operating Manual, §2B-08-120, 20] The ILS approach mode automatically intercepts, captures, and tracks a front course localizer and glideslope beam, using the selected navigation source displayed on the coupled PFD. The ILS navigation source is selected using the display controller. The GS mode does not capture until after LOC has been captured.
Figure: ILS Approach Mode, from G450 Aircraft Operating Manual, §2B-08-00, Figure 31.
In blue needles (Long Range Nav) you should see the ILS identifier in the bottom right of the PFD. Should, but for some reason not always. Once in green needles (Short Range Nav) should see the ILS identifier move to the NAV box on the right. Should, but again for some reason, not always.
Figure: ILS LOC Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 32.
[G450 Aircraft Operating Manual, §G450 OM 2B-08-120, 21] When the aircraft reaches the localizer beam sensor trip point, as shown below, the FGC automatically drops the heading select mode and switches to the LOC capture phase. The GS mode stays armed until the GS beam deviation is reduced to within the capture window.
Figure: ILS LOC Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 33.
Figure: ILS GS Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 34.
[G450 Aircraft Operating Manual, §2B-08-120, 22] When the aircraft reaches the vertical beam sensor trip point, the FGC automatically drops any other vertical mode that was in use and automatically generates a pitch command to track the glideslope beam. The FGC can capture GS from above or below the beam, as shown below.
Figure: ILS Glideslope Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 35.
Figure: ILS Dual Couple Approach Mode, from G450 Aircraft Operating Manual, §2B-08-00, Figure 36.
[G450 Aircraft Operating Manual, §2B-08-120, 23] During the tracking phase of an ILS approach, as shown below, the system uses landing aid flight path information from both the pilot and copilot PFD. This flight segment of the approach phase is automatically initiated and it occurs at 1200 ft radio altitude.
The dual couple mode PFD for the pilot and the copilot, shown below, requires that all of the following conditions are satisfied.
At dual couple transition the following events occur:
In the dual couple mode, shown below, the high priority FGC (i.e., the FGC selected on the display controller (sensor page)) averages the radio data from the pilot and copilot NAV sources. If one navigation receiver fails, or if there is an unflagged miscompare between the NAV receivers, the approach mode continues. The high priority FGC sends identical FD commands (based on the average radio deviations) to both pilot and copilot PFDs in the dual couple mode.
Navigation failures in the dual couple mode result in the following automatic reconfigurations.
Figure: ILS Dual Couple Approach, from G450 Aircraft Operating Manual, §2B-08-00, Figure 37.
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Aircraft Service Change 007C, Maximum Landing Gross Weight, 58,500 pounds, Category C, Provisions, October 26, 2011