Radio Navigation
Ground aids
VOR transmits 108.0–117.95 MHz, radials are magnetic and reception is line-of-sight. DME gives slant range, over-reading most overhead the station. NDB/ADF gives a bearing but suffers night effect, static and coastal refraction. ILS localiser is 108–112 MHz and glidepath 329–335 MHz; a 3° path gives about 300 ft per nautical mile.
GNSS and RNAV
GNSS position depends on RAIM; if RAIM is unavailable the navigation function may be lost. RNP specifies on-board performance monitoring and alerting; RNAV defines a path in space.
Intercepts and tracking
Set the OBS to the radial you want with the correct TO/FROM sense, fly toward the needle, then correct for drift. Reverse sensing appears when the reciprocal is set.
Worked example
On a 3° ILS glidepath with the threshold at 100 ft, at 5 NM DME you should be about 100 + (5 × 300) = 1,600 ft. At 3 NM, about 1,000 ft. Comparing height with DME catches false glidepath capture.
Traps
Confusing a radial with a bearing to the station; forgetting DME is slant range and over-reads close in; capturing a false glidepath; ignoring NOTAMs for navaid outages.