Another VOR Believer
I read Larry Anglisano’s commentary on GPS outages in the November 2024 Aviation Consumer and can weigh in. I have had GPS just go away on me while flying several times and even while flying IFR. Sometimes it is the military jamming GPS for testing. Other times there was no obvious explanation. I even had one GPS outage while IFR over the CONUS when the GPS signal went away (military jamming)—and the next VOR was out of service. At that point all you can do is say, “Hey center, I need a vector to my next fix.”
Regardless, the answer is that any aircraft that will be flying IFR in the system needs VOR and ILS. Best to make sure that the VOR/ILS receiver has ARINC 429 output to make it easy to integrate with modern EFIS displays. That narrows things down considerably when it comes to equipment.