Navigation - Flight Planning, Charts, Magnetism and the Wind Triangle
The Navigation paper tests whether you can turn a route, a chart, a forecast wind and the aircraft's fuel and performance figures into a flight plan you can actually fly. Expect chart work and scale, magnetism, the wind triangle, flight-computer arithmetic, time conversion and the basics of radio navigation.
Chart work
- The ICAO 1:500 000 topographical chart is the standard VFR planning chart. At that scale 1 cm = 5 km, so 1 NM measures about 3.7 mm.
- Measure tracks with a protractor against the nearest meridian, not the chart edge; meridians converge, so grid north is not true north across a large sheet.
- Note isogons (lines of equal magnetic variation), obstacles, controlled airspace and prohibited areas before drawing the route.
Magnetism
- Variation is the angle between true and magnetic north at your position, taken from the chart. Deviation is the aircraft's own compass error, taken from the compass swing card.
- True to magnetic: add westerly variation, subtract easterly. Magnetic to compass: add easterly deviation, subtract westerly.
Wind triangle
- Track plus wind gives heading and groundspeed. Drift is the angle between heading and track: drift ≈ arcsin(crosswind ÷ TAS).
- Wind from the left pushes you right, so heading = track − drift when drift is right.
Worked example
True track 090°, TAS 100 kt, wind 360°/20 kt, variation 1°W, deviation 2°E. The wind is 90° off track: crosswind 20 kt, headwind nil. Drift = arcsin(0.20) ≈ 11.5° right, so heading ≈ 078°(T). Groundspeed = 100 × cos 11.5° ≈ 98 kt. True to magnetic: 078 + 1 = 079°(M). Magnetic to compass: easterly deviation subtracts, giving 077°(C).
Traps that cost marks
- Applying wind to the magnetic track, or applying variation before the wind triangle.
- Reversing the deviation sign; confusing deviation (aircraft) with variation (Earth).
- Quoting a chart distance in kilometres when the answer must be nautical miles.
- Using IAS as TAS, or local time instead of UTC - Nigeria keeps UTC+1 all year.
- Omitting fixed reserve and taxi fuel from the fuel log.