FAA Commercial Pilot Airplane (CAX)Navigation and Flight PlanningEasy
On a sectional chart, a pilot notices a dashed line labeled '10°W' crossing the planned route. What does this line represent?
- AAn agonic line where magnetic variation is zero
- BA line connecting points of equal magnetic variation, known as an isogonic line
- CThe boundary of a Military Operations Area
- DA line connecting points of equal magnetic deviation
Show answer & explanationAnswer & explanation
Correct answer: B. A line connecting points of equal magnetic variation, known as an isogonic line
Isogonic lines on aeronautical charts connect points having the same amount of magnetic variation, shown here as 10° West. These lines allow pilots to determine the variation to apply when converting true courses to magnetic courses.
Why the other options are wrong
- A. An agonic line specifically represents zero variation, not 10°W.
- C. Military Operations Areas are shown with magenta boundary symbols, not variation lines.
- D. Deviation is aircraft-specific and comes from the compass correction card, not charted lines.
Isogonic Line
A line on a chart connecting points of equal magnetic variation, used to determine the correction needed when converting true course to magnetic course.
- Labeled with the variation value and direction, e.g., '10°W'
- The agonic line specifically marks zero variation
- Deviation, in contrast, is unique to each aircraft's compass and instruments
Memory trick: Isogonic = equal variation, not zero