Radio Navigation and Navigation Aids
Ground-based aids
Candidates must understand the operating principles, indications, and limitations of VOR, DME, NDB/ADF, ILS, and marker beacons. For VOR, know the cone of confusion, line-of-sight limitations, and that the CDI shows course deviation, not heading. For DME, know slant-range error (largest at high altitude and close range) and that DME gives distance from the station, not along-track distance unless overhead. For NDB/ADF, know night effect, coastal refraction, static interference, and quadrantal error.
ILS specifics
Know the localizer (108.10–111.95 MHz, 90 Hz/150 Hz modulation, course width typically 5° full scale) and glideslope (329.15–335.0 MHz, nominally 3°). Understand the meaning of the decision altitude/height, the missed approach point, and the difference between CAT I, II, and III minima. Traps: assuming glideslope indications remain usable outside published coverage; confusing a localizer back course with a usable approach; treating an ILS as a precision approach when only lateral guidance is available.
Area navigation
RNAV and RNP differ in the requirement for on-board performance monitoring and alerting: RNP requires it, RNAV does not. Know the meaning of RNAV 5, RNAV 1, RNP 1, and RNP APCH (LNAV, LNAV/VNAV, LPV). A frequent trap is assuming an RNP AR approach can be flown without specific approval.
Worked rule of thumb
When a question gives a VOR radial and asks for the aircraft's position relative to the station, draw the station, the selected radial, and the CDI deflection. A centered CDI with a "TO" indication means the aircraft is on the selected radial inbound; with "FROM", outbound. Never use the OBS setting alone to infer position.
Practice habit
For each aid, write three lines: what it transmits, what the cockpit shows, and what can degrade it.