Navigation
Domain 4 tests navigation fundamentals that affect clearances: track, heading, variation, VOR/DME, NDB, ILS, RNAV and RNP. You need to convert between true and magnetic values and recognise when a navigation aid or PBN specification changes the usable route structure.
Core concepts
Track is the path over the ground; heading is where the nose points. Drift is the angle between them. Variation is the angle between true and magnetic north; east variation is subtracted when converting true to magnetic. A VOR radial is a magnetic bearing from the station. DME gives slant range, which is greater than ground distance at high altitude. An ILS provides lateral and vertical guidance; its localiser and glide path must be protected from interference.
PBN
RNAV and RNP define navigation specifications. RNP includes on-board performance monitoring and alerting; RNAV does not necessarily. RNAV 5, RNP 1 and RNP APCH are common specifications, each with its own containment and equipment requirements.
Worked example: track 090°T, variation 4°E, wind 360/30, TAS 300 kt. Magnetic track is 090 − 4 = 086°M. The wind is from the left, so the aircraft drifts right; the wind correction angle is arcsin(30 ÷ 300) ≈ 6° left. True heading is 084°T and magnetic heading is 080°M. Groundspeed is √(300² − 30²) ≈ 298 kt.
Traps: applying variation in the wrong direction; confusing a VOR radial with a true bearing; treating DME slant range as ground distance; assuming RNAV and RNP have identical monitoring requirements.