FAA Flight Instructor Airplane (FIA)Navigation and AirspaceHard
A pilot plotting a long cross-country route on a Lambert conformal conic sectional chart draws a straight line between the departure and destination airports. This straight line most closely approximates:
- AA rhumb line of constant magnetic heading
- BA great circle route, the shortest distance between the two points
- CAn isogonic line connecting equal magnetic variation
- DA great circle route requiring no heading changes en route
Show answer & explanationAnswer & explanation
Correct answer: B. A great circle route, the shortest distance between the two points
The Lambert conformal conic projection used for sectional charts closely approximates a great circle as a straight line, making it convenient for plotting the shortest route between two points. However, because the great circle heading changes continuously, pilots typically break long routes into segments and adjust heading periodically.
Why the other options are wrong
- A. A rhumb line follows a constant heading but is generally a longer distance and appears curved on this projection.
- C. Isogonic lines relate to magnetic variation, unrelated to route plotting.
- D. Great circle routes still require periodic heading changes since true course changes along the route.
Great Circle vs. Rhumb Line
A great circle is the shortest path between two points on a sphere; a rhumb line maintains a constant heading but is longer.
- Lambert conformal conic charts approximate great circles as straight lines
- Rhumb lines appear curved on Lambert charts but straight on Mercator charts
- Great circle routes require heading changes along the route
Memory trick: 'Great circle = the shortcut, but the heading keeps shifting'