Radio Navigation
What the exam tests
Radio Navigation tests VOR, DME, NDB/ADF, ILS, GNSS, RNAV/RNP, radar, and transponder use, including interpretation of cockpit indications and approach geometry.
Core rules
- A VOR radial is a magnetic bearing from the station. With the OBS set to the desired radial, a centred CDI with a TO indication means the aircraft is on that radial tracking to the station; FROM means tracking away.
- DME measures slant range, not horizontal distance. The error is greatest when close to and high above the station.
- ILS localizer gives lateral guidance; glideslope gives vertical guidance, normally 3°. Marker beacons or DME identify fixes. Decision altitude is referenced to the ILS approach.
- NDB/ADF bearings are relative to the aircraft; the ADF needle points to the station. Bank causes dip error.
- GNSS RNAV/RNP requires RAIM and the correct database; RNP also requires onboard performance monitoring and alerting.
Worked example
On a 3° ILS glideslope, what height should the aircraft be at 4 NM from the threshold? 4 NM = 24,304 ft. Height ≈ 24,304 × tan 3° ≈ 24,304 × 0.0524 ≈ 1,274 ft above threshold. Add threshold elevation and any charted reference to obtain the indicated altitude.
Traps
Do not confuse a VOR radial with a heading. Do not treat DME as horizontal distance close to the station. Do not fly a false glideslope or reverse-sensing localizer indication. Do not use GNSS without checking RAIM and database validity.