Radio Navigation
Radio Navigation tests VOR, DME, ILS, NDB/ADF, GNSS and radar. The exam asks what the cockpit indicator shows and what action follows.
VOR/DME
A VOR radial is a line from the station; the CDI centres when the selected OBS matches the radial. TO/FROM indicates whether the selected course leads to or from the station. DME gives slant range; at high altitude it reads greater than ground distance.
ILS and GNSS
Localizer gives lateral guidance, glideslope vertical; a 3° glideslope is about 300 ft per nautical mile. GNSS requires RAIM or equivalent integrity; check it before approach.
Worked example
You are west of a VOR on the 270 radial and want to fly inbound. Set OBS 090; the CDI centres with TO. If DME reads 10 NM at 6000 ft, ground distance ≈ √(10² − 1²) ≈ 9.95 NM.
Traps
Reverse sensing; forgetting glideslope is not a precision lateral path; using DME as ground distance; assuming GNSS is always available.