In addition, it was mentioned that GPS cannot be used as primary navigation. Actually, it very definately CAN, at least with US registered aircraft.
411A
You may be right but I thought I had read a recent American (NASA or FAA or something) study that concluded GPS could not be used as a primary navigation aid in the forseeable future. Or perhaps what I'm trying to say is it can't be used exclusively. The main reason is that the accuracy varies according to where you are, and when you are there, versus the current satellite constellation. This means in some situations there is insufficient accuracy available to you. Also interference is still a risk.
I can't see how
practically you can have a primary navigation system that means you can't take off for 4 hours while you wait for the right satellite configuration for all route sectors.