Radio Navigation: Ground Aids, Radar and GNSS
VOR and DME
Understand the VOR radial concept: a selected radial is a line from the station, and the CDI sense reverses depending on whether you are tracking to or from. Trap: confusing the OBS-selected radial with the aircraft's actual bearing from the station. Use the "to/from" flag and the ambiguity of radials. DME gives slant range, which reads high near the station and approximates ground distance at high altitude; DME groundspeed is only valid in steady tracking.
NDB/ADF
Know relative bearing, magnetic bearing and the QDM/QDR relationship. The ADF needle points to the station relative to the aircraft heading; convert relative to magnetic bearing by adding heading. Beware of coastal refraction, night effect, and thunderstorm interference.
ILS
Learn the localiser (108–112 MHz, lateral) and glidepath (UHF, vertical) frequencies, the coverage sectors, and the meaning of decision height versus decision altitude. Know the fly-up/fly-down and the marker beacons or DME distance fixes.
Radar and GNSS
Understand primary and secondary radar, and how GNSS uses ranging from satellites with RAIM for integrity. Know the difference between accuracy, integrity, availability and continuity.
Worked example: Aircraft heading 090°M, ADF relative bearing 030° → magnetic bearing to station = 090 + 030 = 120°M; the QDM is 120°M.