Radio Navigation
Radio Navigation tests VOR, DME, NDB, ILS, GNSS and area-navigation systems, including the interpretation of cockpit indications and the limitations of each aid.
Core concepts
- A VOR radial is a magnetic bearing from the station; the CDI shows the selected radial and TO/FROM sense.
- DME measures slant range, so indicated distance is greater than ground distance and increases with altitude.
- ILS localizer gives lateral guidance; glideslope gives vertical guidance; both must be monitored for full-scale deflection and warning flags.
- GNSS/RNAV requires RAIM or equivalent integrity monitoring; RNP adds on-board performance monitoring and alerting.
Worked example
An aircraft is 10 NM ground distance from a DME station at 6,000 ft. Slant range = √(10² + 1²) ≈ 10.05 NM, using 6,000 ft ≈ 1 NM. The error is small at this distance but becomes significant close to the station and at high altitude.
Traps
- Confusing a VOR radial with the aircraft heading.
- Treating DME as ground distance.
- Following a glideslope that is not associated with the correct localizer.
- Ignoring RAIM warnings or GPS jamming/spoofing.
- Reverse sensing when tracking a radial outbound with the OBS set incorrectly.