Radio Navigation
Radio Navigation tests VOR, NDB/ADF, DME, ILS, GNSS, radar and performance-based navigation. The aim is to interpret cockpit indications correctly and to understand the limitations of each aid.
VOR and DME
A VOR radial is a magnetic bearing from the station. The CDI shows course deviation; full-scale deflection is typically 10 degrees. With the OBS set and the CDI centred, TO/FROM tells you whether the selected course takes you to or from the station. DME measures slant range, so it reads higher than ground distance when close in and high.
NDB and ILS
An ADF shows relative bearing; the magnetic bearing to the station is heading plus relative bearing. An NDB is affected by thunderstorm activity, night effect and terrain. ILS gives lateral guidance from the localiser and vertical guidance from the glideslope, normally about 3 degrees. Marker beacons or DME fix the approach positions.
GNSS and PBN
GNSS provides position, track and ground speed. RAIM checks integrity; if RAIM is unavailable, the approach may not be usable. PBN uses RNAV and RNP specifications, with RNP requiring on-board performance monitoring and alerting.
Worked example
You tune a VOR, set OBS 090 and the CDI is centred with TO shown. The selected course is 090 towards the station. Because the radial is the bearing from the station, you are on the 270 radial. If the CDI later deflects left while tracking 090, the selected course is to your left; turn left to rejoin, ensuring the heading change is coordinated.
Traps
Confusing radial with bearing; reverse sensing when tracking a course away from the station; treating DME as ground distance; assuming GNSS is always available without RAIM; ignoring NDB night effect.