Radio Navigation
This domain covers ground-based and satellite navigation aids: NDB/ADF, VOR, DME, ILS, radar and GNSS/RNAV. Questions test indications, limitations and correct interpretation.
NDB and VOR
- ADF points to the NDB; the tail indicates bearing. NDB is affected by night effect, thunderstorms and terrain.
- VOR gives the magnetic bearing from the station. The OBS selects the radial; TO/FROM shows whether you are tracking to or from.
- DME gives slant range; error is greatest at high altitude and close range.
ILS and GNSS
- Localiser gives lateral guidance; glidepath is normally 3°, about 300 ft per NM.
- Marker beacons give distance fixes; modern installations may use DME or GNSS.
- RAIM checks GNSS integrity; without RAIM, do not rely on GNSS for approach.
Worked example
OBS 090, CDI centred, TO/FROM shows FROM. The aircraft is on the 090 radial, outbound from the station. If the CDI deflects left, the selected radial is to the left; turn left to centre it.
Traps
- Reverse sensing when tracking a VOR radial with a bearing pointer.
- Misreading TO/FROM.
- Following a false glidepath above the true 3° path.
- Forgetting that DME is slant range, not ground distance.
- Trusting GNSS without checking RAIM or NOTAMs for jamming.