Mxsmanic wrote:
Andrew Sarangan writes:

So what instrument would you suggest we use for true headings?

A combination of INS and GPS would work. It would be at least as
accurate as a compass.

Accuracy isn't the problem. Would it be as reliable?
Would it be affordable and workable in airplanes that lack
electrical systems? And would it work when those
electrical systems failed?

If you're talking about high budget commercial aviation, any
nav system that has the processing power to decode the
GPS signals has the power to apply a local magnetic
deviation to its heading or course output. Updates to
the magnetic deviation can be distributed as needed
with the updates to the nav database. So for these
users, it's sort of arbitrary which reference is used,
as long as there is an agreed upon reference.

For the gliders, Piper Cubs, and other moderate budget
flyers, the price and reliability differences between a
compass and an INS weigh significantly in favor of the
compass.

There is the further issue of inertia. Every pilot flying today
learned to use magnetic headings. Every airplane cockpit
has an instrument (or several instruments) to prominently
display the magnetic heading to the pilot. To convert
wholesale would entail a period of minor confusion at
least.

Finally, what problem would it solve? The shifting of
the Earth's magnetic poles is slow, relatively
predictable, and something we have lived with for
awhile. While true headings may be more elegant
and stable over the very long term, that elegance
doesn't add much practical value.

--Rich