writes:

And if you are really serious about the subject, the run of the mill flare
will cause a temporary signal loss, which aviation GPS will detect, and
there is no particular reason to suspect that the current sunspot cycle
will prove to be anything other than run of the mill.

If your GPS becomes unreliable, and you have no other means of navigation,
what do you do? Just knowing that GPS has failed doesn't help you much if you
have no back-up.