Radio Navigation
What the exam tests
Radio navigation tests VOR, DME, NDB/ADF, ILS, GNSS, radar services and area navigation. The exam expects interpretation of cockpit indications, station passage, CDI sensing and approach limits.
Core systems
- VOR gives bearing from the station; the CDI shows course deviation and TO/FROM. A selected radial is the bearing from the station.
- DME gives slant range, not ground distance; error is greatest close to the station at high altitude.
- NDB/ADF gives relative bearing; the ADF needle points to the station.
- ILS localiser gives lateral guidance, glideslope gives vertical guidance; both must be within limits.
- GNSS gives position, track and groundspeed; RAIM and database validity must be checked.
Worked example
On a 3-degree ILS glideslope at 5 DME from the threshold, nominal height is approximately 5 nm x tan 3 degrees = 5 x 0.0524 = 0.262 nm, or about 1,590 ft above threshold elevation. At 5 DME the aircraft should be near 1,600 ft, not 2,000 ft. If the aircraft is high, reduce power and intercept from below; do not dive to the glideslope.
Traps
Do not reverse the VOR TO/FROM interpretation. Do not use DME as exact ground distance. Do not chase false glideslope signals. Do not continue an ILS beyond the missed approach point without the required visual reference.