Navigation
Navigation tests dead reckoning, the wind triangle, chart and compass work, and the use of radio and satellite aids to confirm where you actually are.
Charts and direction
Mercator charts show a rhumb line as a straight line, which is why they suit radio navigation; Lambert conformal conic charts show a great circle nearly straight and are common for topographical work. Scale errors cost marks - always measure in the units the chart uses. True direction becomes magnetic by applying variation (isogonals on the chart), and magnetic becomes compass by applying deviation from the compass swing card. "Variation east, magnetic least"; "variation west, magnetic best".
The triangle of velocities
Heading and TAS combined with wind velocity give track and groundspeed. Drift is the angle between heading and track. The 1-in-60 rule: a track error of 1 NM in 60 NM is 1°. For an off-track error, degrees of correction back to destination ≈ (distance off track ÷ distance travelled) × 60, plus the same again to converge.
Worked example
True track 090°, TAS 120 kt, wind 000°/20 kt. The wind blows from the north, so its crosswind component perpendicular to the track is the full 20 kt, pushing the aircraft south (right of track); the along-track component is zero. Drift = arcsin(20 ÷ 120) = 9.6° right. To hold track, steer left: heading = 090 − 9.6 = 080°T. Groundspeed = 120 × cos 9.6° ≈ 118 kt. If variation is 8°W, magnetic heading = 080 + 8 = 088°M.
Practical technique
Log heading, time, fuel and ETA at each turning point; update ETA from actual groundspeed; use radio aids and GNSS to fix position rather than to replace DR. Note that GNSS accuracy depends on RAIM and satellite geometry.
Traps that cost marks
Applying variation the wrong way; treating wind direction as where the wind is going; applying deviation to a magnetic heading instead of a compass heading; and forgetting that great circle and rhumb line tracks diverge on long legs.