Navigation
Navigation covers planning and determining position in flight: dead reckoning, the wind triangle, magnetism, altimetry, radio navigation aids, performance-based navigation and chart work.
Direction and magnetism
- True to magnetic: magnetic = true minus easterly variation (variation east, magnetic least). Deviation is then applied to magnetic to obtain compass heading.
- Isogonals join points of equal variation; magnetic dip affects compass behaviour at high latitude.
The wind triangle
- Heading and TAS combined with the wind vector give track and ground speed. Drift is the angle between heading and track; correct into wind.
Radio navigation
- VOR gives a radial from the station; it is line-of-sight, about 1° wide per 60 NM, and has a cone of confusion overhead.
- NDB/ADF is affected by night effect, coastal refraction and thunderstorm interference; the bearing is relative to the aircraft heading.
- DME measures slant range, which always exceeds the ground distance.
- ILS localizer is a narrow beam of roughly 3–6° total width; the glideslope is normally 3°.
- GNSS/RNAV relies on RNP values and a RAIM check before an approach.
Altimetry
- Set 1013.2 hPa above the transition level and QNH below the transition altitude; the transition layer lies between them.
Worked example
TAS 120 kt, required track 090°(T), wind 240/30. The wind blows towards 060°, so its component along track is 30 × cos 30° = 26 kt tailwind and its crosswind component is 30 × sin 30° = 15 kt from the right. Drift = arcsin(15/120) ≈ 7°, so the heading is 097°(T). Ground speed = 120 × cos 7° + 26 ≈ 145 kt. With 2°E variation, the magnetic heading is 095°M before deviation is applied.
Traps
- Applying variation in the wrong direction.
- Using TAS as ground speed, or DME slant range as ground distance.
- Forgetting that drift must be corrected into wind, not away from it.