For most of aviation history, the NDB Approach was an exercise in faith that the electrons would behave and allow you to live and fly another day, a hope that was in vain for many. These days, we have a lot more electrons working in concert with satellites to keep us out of the dirt. Still, you are better off flying any other instrument approach. If you insist on flying the NDB approach, refer to NDB 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.
You can no longer fly an NDB as a GPS overlay in the United States. Why? See Procedures & Techniques / GPS. If flying an NDB approach in the United States without “GPS” in the title, you must have the ground-based navigation aid tuned, identified, displayed, and monitored. Internationally, if the approach is referenced to WGS-84, you might be able to depending on that State's rules.
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 (LDSP), from Eddie's aircraft.
Approach selection is made either through the MCDU (NAV > ARRIVAL) or the NAV display.
Photo: DU arrival page (LDSP), 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.
The FMS will not automatically preview an NDB approach.
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