In article ,
Mxsmanic wrote:

Roy Smith writes:

Unreliable? The magnetic compass is about as reliable is it gets. There's
one moving part, no power source, and the Earth's magnetic field is good
for another few thousand years. What's unreliable about that?

Put a chunk of metal next to it, and you'll see. Turn the aircraft,
and see if the compass instantly changes position.

All devices have failure modes. Of course there are things which will
interfere with a magnetic compass, but I'll still stand by my statement
that it's about as reliable as a piece of technology can get.