Radio Navigation Aids and Global Navigation Satellite Systems
Ground-based aids
The Radio Navigation Aids and GNSS domain tests how you use VOR, DME, NDB/ADF, ILS and satellite navigation. A VOR radial is a line extending FROM the station; the CDI shows whether you are left or right of the selected radial. DME measures slant range, which is slightly greater than ground distance and increases with altitude. An ADF shows relative bearing; magnetic bearing to the station = aircraft magnetic heading + relative bearing. ILS provides localizer lateral guidance and glideslope vertical guidance down to a decision altitude or height. GNSS receivers use satellite ranging; RAIM checks whether the available geometry supports integrity, and SBAS can augment GPS. Use an approved database and check NOTAMs for outages.
Worked example
An aircraft heading 030°M has an ADF relative bearing of 060°. The magnetic bearing to the NDB is 030° + 060° = 090°M. If the pilot turns to 090°M and the relative bearing remains 000°, the aircraft is tracking toward the station. This is a simple relative-bearing calculation; wind will cause drift unless heading is adjusted.
Traps
VOR radials are FROM the station, not TO it. Reverse sensing can occur when the selected course is behind the aircraft. DME slant range is not ground distance; at high altitude and close range the error is largest. Do not assume GPS integrity without RAIM or an equivalent check. Do not fly an ILS glideslope or localizer beyond protected areas without the correct chart and minima.