General Navigation
What this domain tests
General Navigation tests chart work, magnetism, the wind triangle, great circles and rhumb lines, time and scale. Expect calculations with magnetic variation and deviation, plus questions on chart projections.
Core rules
- True heading plus or minus variation = magnetic heading; magnetic heading plus or minus deviation = compass heading. East is least: with easterly variation, magnetic is less than true.
- Wind triangle: track and ground speed come from TAS and the wind vector. Drift is the angle between heading and track.
- A great circle is the shortest path; a rhumb line is a constant track but longer. Lambert conformal conic is used for many topographical charts; Mercator is a rhumb-line chart.
- 1 minute of latitude = 1 nautical mile; 1 minute of longitude = 1 nm x cos(latitude).
- Time: UTC is used in flight planning; local time zone changes must be applied to ETA.
Worked example
Heading 090 degrees (T), TAS 200 kt, wind 360/20 kt. The wind is a direct crosswind from the left, so GS = square root of (200 squared minus 20 squared) = square root of 39,600, about 199 kt. Drift = inverse sine of (20/200), about 5.7 degrees to the right, so the heading to maintain track 090 is about 084 degrees (T). With 8 degrees E variation, magnetic heading = 084 minus 8 = 076 degrees (M).
Traps
Applying variation in the wrong direction; using the wind direction as 'to' rather than 'from'; forgetting that a chart scale in centimetres must be converted; treating a rhumb line as the shortest route.
Key habit
Draw the wind triangle to scale before touching the calculator; the diagram catches sign errors.