Radio Navigation
What the exam tests
Radio Navigation covers VOR, DME, ILS, NDB/ADF, GNSS, RNAV, RNP, radar and transponder use, including interpretation of cockpit indications and approach guidance.
Core rules
- VOR gives magnetic bearing from the station; the CDI shows the selected radial and whether you are left or right of it.
- DME gives slant range, which is greater than ground distance at high altitude and close range.
- ILS consists of localiser for lateral guidance and glideslope for vertical guidance; a 3° glideslope gives about 300 ft per nautical mile.
- NDB/ADF gives relative bearing; the ADF needle points to the station, and heading must be added to obtain the magnetic bearing.
- GNSS/RNAV requires RAIM or equivalent integrity monitoring; RNP adds on-board performance monitoring and alerting.
Worked example
On a 3° ILS glideslope at 140 kt groundspeed, required rate of descent ≈ groundspeed × 5 = 700 ft/min. Reasoning: the 1-in-20 approximation for a 3° path gives about 300 ft per NM; at 140 kt, that is 140 NM/hr, so 140 × 300/60 ≈ 700 ft/min. Adjust for actual groundspeed, not indicated airspeed.
Traps
Using indicated airspeed instead of groundspeed for glideslope descent; reverse sensing when tracking a VOR radial outbound; treating DME as ground distance; ignoring ILS critical-area protection; assuming GNSS integrity without checking.