Air navigation (technical aspects)
Air navigation - technical aspects
This domain tests the calculations behind navigation: Earth geometry, magnetism, the wind triangle, radio aids and chart projections.
Core rules
- A great circle is the shortest path; a rhumb line is a constant track. Mercator exaggerates high-latitude scale; Lambert conformal conic is common for aeronautical charts.
- True course ± variation = magnetic course; "variation east, magnetic least" (subtract easterly variation).
- Wind triangle: heading corrects for drift; GS is TAS combined with wind. Drift = arcsin(crosswind/TAS).
- VOR radials are magnetic; DME gives slant range, so it overreads compared with ground distance, especially close in.
- NDB/ADF: relative bearing + heading = magnetic bearing to station; QDM is magnetic to the station, QDR magnetic from it.
- GNSS: RAIM checks integrity; waypoints and RNAV/RNP define containment.
- Flight planning: true course → magnetic heading → compass heading, applying wind, variation and deviation in that order.
Worked example
TC 000°, TAS 100 kt, wind 090°/20 kt. Crosswind = 20 kt from the right. Drift = arcsin(20/100) = 11.5°, so true heading = 360 − 11.5 = 348.5°. Ground speed = √(100² − 20²) = 98 kt. With 10°E variation, magnetic heading = 348.5 − 10 = 338.5°.
Traps
Applying variation in the wrong direction; confusing heading, track and bearing; using TAS as ground speed; treating a VOR radial as true; and forgetting that DME is slant range, not distance along the ground.