What is an Agonic line anyway?

Posted by on Jun 8, 2012 | Comments Off on What is an Agonic line anyway?

Remember sectional charts? The latitude/longitude lines are drawn in reference to TRUE north however, the compass seems to prefer MAGNETIC north so we need to know what the difference is between true and magnetic north to accurately plan any given flight. The difference between the two is magnetic declination (pilots call it magnetic variation) and it is represented on sectional charts by magenta dashed lines with the amount of variation for the area labeled in degrees with an E or W after (remember “east is least, west is best” from your private pilot training?) Ex. KVLD is between 4 W and 5 W. By the way, magnetic north is a moving target. When I began flying in the Valdosta area, the variation was 3 W. These lines of variation are called isogonic lines and where there is no variation, the line is called an agonic line. It currently crosses our latitude (on this side of the planet) about 15 miles west of Biloxi, MS. These are not limited to sectional charts. Most modern maps will have some way of showing it’s user the difference between true and magnetic north. In our area, if you forgot to account for it, you’d probably still find your destination but what about the state of Washington? The difference there is as much as 20 degrees!

Safe Travels,