FAA Commercial Pilot Airplane (CAX)Navigation and Flight PlanningEasy
A sectional chart shows an isogonic line indicating 8° east variation along a planned route. The pilot's true course, measured with a plotter, is 250°. What magnetic course should the pilot use before applying compass deviation?
- A242°
- B258°
- C233°
- D250°
Show answer & explanationAnswer & explanation
Correct answer: A. 242°
East variation is subtracted from true course to get magnetic course: 250° − 8° = 242°. The memory aid 'East is least' applies when converting from true to magnetic.
Why the other options are wrong
- B. This adds the variation instead of subtracting, which is used for westerly variation.
- C. This subtracts too much variation (17° instead of 8°).
- D. This ignores variation entirely.
True Course to Magnetic Course
Converting a true course to a magnetic course requires applying the magnetic variation shown by isogonic lines on a sectional chart.
- East variation: subtract from true course ('East is least')
- West variation: add to true course ('West is best')
- Deviation is applied afterward to get compass heading
Memory trick: East is least, West is best