Navigation - General Navigation
What the exam tests
General navigation tests the Earth's shape, coordinate systems, chart projections, great circles, rhumb lines, time and magnetism. Calculations must be shown, not guessed.
Core rules
- 1 minute of latitude = 1 NM; 1 degree = 60 NM.
- Distance along a parallel = change of longitude (minutes) × cos(latitude).
- Great circle is the shortest track; rhumb line is constant track but longer except on the equator/meridians.
- Magnetic variation east is subtracted from true to get magnetic; deviation is aircraft-specific.
- Lambert conformal conic is standard for en-route charts; scale is correct along standard parallels.
Worked example
You fly along 60°N from 010°E to 020°E. Change of longitude = 10° = 600 minutes. Distance = 600 × cos 60° = 600 × 0.5 = 300 NM. If true track is 090°, and variation is 3°E, magnetic track = 090° − 3° = 087°M. Reasoning: the parallel is a small circle, so departure must be reduced by cos latitude; variation is applied true-to-magnetic, not the other way round.
Traps
Using cos latitude on a meridian; adding easterly variation instead of subtracting; confusing departure with change of longitude; using a rhumb line for a polar route; ignoring chart scale changes away from standard parallels.