writes:

The point MX misses is that there is no such thing as a Nav device certified
for VFR flight other than the Mark I eyeball and a chart; everything else
is backup for VFR flight.

I haven't missed it, but many pilots do, since they start relying on other
navigation methods as their primary methods regularly--especially GPS.

Most people (and not just pilots) have only a very vague notion of how GPS
works, and consequently have far more confidence in the system than they
should have. And it's easier to look at a GPS display (with a map) than out
the window. So people come to rely on GPS for primary navigation, with
occasionally unpleasant results. It happens for both automobile drivers and
pilots (and boaters, etc.), but the potential consequences of overreliance on
GPS are much more grave for pilots than they are for drivers.

This is true even for certified GPS units. Certification does not guarantee
reliability except in a few narrowly-defined circumstances.