FAA Sport Pilot Airplane (SPA)Airspace and NavigationMedium
A pilot notices a dashed line on a sectional chart labeled '10°E' running roughly north to south across the planned route. What does this line represent, and how does it affect flight planning?
- AThe lateral boundary of a Class E transition area
- BA time zone boundary requiring the pilot to adjust the clock during flight
- CA Victor airway centerline connecting two VOR stations
- DAn isogonic line connecting points of equal magnetic variation, used to convert between true and magnetic courses
Show answer & explanationAnswer & explanation
Correct answer: D. An isogonic line connecting points of equal magnetic variation, used to convert between true and magnetic courses
An isogonic line is a dashed line on aeronautical charts connecting points of equal magnetic variation. The labeled value (e.g., 10°E) tells the pilot how many degrees to add or subtract when converting a true course to a magnetic course in that area.
Why the other options are wrong
- A. Class E transition areas are shown with shaded magenta vignettes, not degree-labeled dashed lines.
- B. Time zone lines are solid or dashed but labeled with zone names, not variation values.
- C. Victor airways are solid black lines labeled with airway numbers (e.g., V257), not degree values.
Isogonic Line
A dashed line on aeronautical charts connecting points of equal magnetic variation, labeled with the variation value.
- Used to convert true course to magnetic course (TC ± variation)
- An agonic line marks where variation equals 0°
- Variation differs from compass deviation, which is aircraft-specific
- Labeled in degrees East or West of true north
Memory trick: 'East is least, West is best' for applying variation from the isogonic line