PLT320: True and Magnetic North
What code PLT320 covers, why the FAA tests it, and how to study True and Magnetic North before your checkride.
Recall navigation - true north / magnetic north
What this means for your checkride
Charts and headings mix two references for north. True north is the geographic pole; magnetic north is where the compass points, and the two differ by an angle called magnetic variation, shown on charts as isogonic lines. You convert between true and magnetic course by applying the local variation.
Navigation planning is done in true and flown by the magnetic compass, so the FAA tests whether you can apply variation correctly and read isogonic lines off the chart.
The east-is-least, west-is-best rule gets applied backward. To go from a true course to a magnetic course you subtract easterly variation and add westerly variation, and reversing it puts your heading off by twice the variation.
Where to study it
Practice questions on this code
Real questions from the Aviator IQ bank that test this exact area. Answer each to see the correct choice, the full rationale, and the FAA source.
In the Washington, D.C. area the magnetic variation is 10° west. To fly a true course of south, 180°, what magnetic course must the pilot steer?
On a cross-country flight plotted on a sectional chart, what does the true course (TC) represent?
Oral checkride defense
A code on your report is an area the examiner can revisit. Here is how an examiner might probe it, and how to explain it out loud.
Convert a true course of 180 to a magnetic course where variation is 10 west.
Add westerly variation to true to get magnetic: 180 plus 10 is 190 degrees. The rule is east is least, west is best, so I subtract easterly and add westerly variation. I read the local variation from the isogonic line on the sectional.
Why do we plan in true but fly a magnetic heading?
Charts and courses are drawn to true north, but the magnetic compass points to magnetic north, and the two differ by variation. So I plot the true course, apply variation to get magnetic, then apply compass deviation, ending with the heading I actually fly.
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.