The Back Course Localizer continues to offer opportunities for mistakes and nobody has come up with an idea better than the "BC" switch for reverser sensing of the localizer beam. Refer to Normal Procedures & Techniques / Back Course Localizer 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: MCDU arrival page (PHOG), from Eddie's aircraft.
Approach selection is made either through the MCDU (NAV > ARRIVAL) or the NAV display.
Photo: DU arrival page (PHOG), from Eddie's aircraft.
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: Back Course Mode Selection, from G450 Aircraft Operating Manual, §2B-08-00, Pg. 10.
[G450 Aircraft Operating Manual §2B-08-70 ¶;3.] The back course mode is selected by pushing the GP BC button. The flight director generates roll guidance commands for capture and tracking of the BC localizer indicated on the coupled PFD. Pushing the BC button on the guidance panel arms BC if the beam deviation is outside the capture range. After the BC mode has been armed, the flight director disarms the BC mode if the pilot pushes the BC button before the BC mode becomes active. The FD lateral mode transitions to BC CAP as a function of LOC DEV, course angle, distance-to-transmitter, and TAS.
Figure: Back Course Arm, from G450 Aircraft Operating Manual §2B-08-00, Figure 21.
[G450 OM 2B-08-120 ¶14.] The BC mode automatically intercepts, captures, and tracks a BC localizer beam, using the selected navigation source displayed on the coupled PFD. The LOC navigation source is selected using the display controller. In the BC armed mode, the aircraft flies the heading intercept and is armed for automatic BC beam capture.
Figure: Back Course Mode, from G450 Aircraft Flight Manual §2B-08-00, figure 20.
Be careful about the intercept angle. If you are in LRN mode the FMS should do a fine job of leading the turn if your speed is fairly constant. If you are in SRN mode with a large intercept angle, the FMS doesn't seem to grasp the distance to course until it is too late.
Figure: Back Course Tracking, from G450 Aircraft Operating Manual §2B-08-00, Figure 24.
[G450 OM 2B-08-120 ¶16.] The track submode is annunciated the same as BCc capture mode (i.e., no annunciator change occurs at the capture to track mode transition). The track mode follows the capture mode and occurs after the beam deviation is reduced to a minimal value. In the track mode, the flight guidance computer automatically compensates for crosswinds of up to 45° of course error.
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