Radio Navigation
Radio Navigation tests VOR, DME, NDB/ADF, ILS, GNSS, RNAV/RNP, radar and warning receivers. The exam emphasizes what each aid measures, its limitations and correct interpretation.
Core rules
- VOR gives bearing from the station, called a radial; the CDI centres when the selected radial is correct. It does not give distance.
- DME gives slant range; ground distance equals the square root of slant range squared minus height squared.
- NDB/ADF gives relative bearing; magnetic bearing is heading plus relative bearing, with sign care.
- ILS localizer gives lateral guidance and glideslope gives vertical guidance; typical glideslope is 3 degrees.
- GNSS/RNAV uses waypoints; RNP adds on-board performance monitoring and alerting.
- Radar services provide traffic information and separation, not pilot navigation.
Worked example
DME reads 5.0 nm at 6,000 ft. Height is 6,000 divided by 6,076, about 0.99 nm. Ground distance = square root of (5.0 squared minus 0.99 squared) = square root of (25 minus 0.98) = square root of 24.02, about 4.9 nm. The error is small at long range but significant close in.
Traps
- Calling a VOR radial a bearing to the station.
- Using DME slant range as ground distance on approach.
- Following glideslope below minima without visual reference.
- Assuming GNSS integrity without RAIM or RNP alerting.