Radio Navigation and Instrumentation
What the exam tests
Radio navigation covers VOR, DME, NDB/ADF, ILS, GNSS, radar and the interpretation of cockpit indications. Expect questions on radials, bearings, intercepts and approach geometry.
Core rules
- VOR gives a magnetic radial from the station; the CDI shows course deviation, not aircraft heading. 'From' flag means the selected course is away from the station.
- DME gives slant range; at high altitude, DME distance exceeds ground distance.
- ILS localizer 2.5° full scale; glideslope 0.7° full scale; 3° path ≈ 318 ft/NM.
- NDB/ADF gives relative bearing; magnetic bearing = heading + relative bearing.
- GNSS RAIM predicts integrity; approach minima depend on fault detection.
Worked example
On a 3° ILS, DME reads 4 NM from the threshold. Expected height above threshold ≈ 4 × 318 = 1,272 ft. If the aircraft is 1,400 ft, it is about 128 ft high. At 5 NM the same path gives 1,590 ft. Reasoning: the 318 ft/NM rule is a quick cross-check for glideslope; it is not a substitute for the published approach chart.
Traps
Turning to the reciprocal of the selected radial; reading DME as ground distance; using heading instead of track for intercepts; confusing localizer and glideslope sensitivity; forgetting that ADF bearings are relative, not magnetic, until heading is added.