Radio Navigation
Radio navigation questions test the operating principles and limitations of ground-based and satellite aids. Understand VOR: radials, the CDI, and the difference between "on the radial" and "tracking". Know that VOR gives bearing from the station, and that line-of-sight limits range.
DME gives slant range, not ground distance; the error is largest overhead the station. Understand the relationship between VOR and DME for a fix.
ILS: know the localiser (lateral) and glidepath (vertical), the meaning of the decision altitude and the sensitivity of the CDI. Understand marker beacons and the difference between CAT I, II and III minima.
NDB/ADF: the needle points to the station; know relative bearing, magnetic bearing and the effect of thunderstorm activity and night effect.
GNSS: understand the concept of RAIM, the difference between accuracy and integrity, and the effect of satellite geometry on dilution of precision.
Traps: treating DME as ground distance; confusing relative bearing with magnetic bearing; and assuming VOR is unaffected by terrain.
Worked rule of thumb: DME ground distance ≈ √(slant range² − altitude²). At 30,000 ft (about 5 NM) and 100 NM slant range, ground distance is about 99.9 NM - negligible.