Radio Navigation and Communication
Radio navigation and communication
Questions test VOR/DME, ILS, NDB/ADF, GNSS, radar and SSR, plus RT phraseology and lost-communication procedures. Know what each aid measures, its failure modes and the correct readback.
Core rules
- VOR gives a magnetic radial from the station; the CDI must be interpreted with the TO/FROM flag. DME gives slant range, not ground distance.
- ILS localizer gives lateral guidance; glideslope gives vertical guidance. A 3° glideslope is about 300 ft per nautical mile, but the exact height depends on the threshold crossing height.
- Marker beacons and DME fix positions; GNSS and RNP approaches require the specified performance and monitoring.
- SSR codes and phraseology must be read back; lost communication follows the published AIP or ATS procedure.
- Radar vectors do not cancel the pilot's terrain responsibility unless a minimum radar vectoring altitude is provided.
Worked example
On a 3° ILS glideslope at 5 NM DME from the threshold, the nominal height above threshold is about 5 × 300 = 1500 ft. Exact trigonometry gives 5 × 6076 × tan 3° ≈ 1590 ft, so the rule of thumb slightly underestimates. Add the threshold elevation to compare with the altimeter, and remember DME is slant range.
Traps
Do not fly a false glideslope or reverse-sensing back course without the correct equipment. Do not confuse a VOR radial with the aircraft heading. Do not assume a clearance to a fix includes terrain separation. Read back runway, altitude, heading and frequency changes.