Why use other navaids when there is GPS?

[PT6A]

Root,

Maybe you should have a chat with WestJet, they fly in and out of the mountains everyday... not using any ground based navigational aids.

The same can be said for Alaskan Airlines, the company that pioneered RNP AR operations.. It's two Captains going on to set up Naverus (now part of GE Aviation)

I can think of at least one example where a non GPS aircraft flying a VOR approach very nearly ended up in the side of a mountain. Not because of a fault of the crew but a faulty ground based navigational aid.