"M" wrote in message news:
...
On Mar 3, 3:18 pm, "Jon Woellhaf" wrote:

What fixed compass heading would hold to fly from JFK to SFO (assuming no
wind correction)?

Is it a trick math question? It's certain won't be the great circle
route, which has a continuous changing magnetic heading to hold.

Given the difference of magnetic variation between west coast and the
east coast, I'm not certain this can be calculated using a math
formula. Such a magnetic heading can be deduced by a computer
simulation using the brute force method.

This is a very complex mathematical problem, but it could be
solved analytically if a precise description of the earth's magnetic
field were available. To see how involved it gets, look up "affine
connections" in Wikipedia, but that's just the theory!

A numeric solution by successive approximation would yield
an approximate answer. One would calculate an approximation
to the magnetic field using the dashed magnetic variation lines
on the various sectionals & then extrapolate using (say) one-mile
path lengths. Vary the initial magnetic heading from JFK using
Newton's method until you hit SFO with the desired accuracy.

Well, that's what I'd do were I at all interested..!