Radio Navigation

Radio navigation lets you find your position without seeing the ground: from beacons on the ground, from satellites, or from radar on the ground watching you. Even with GPS in every cockpit, VOR, DME and ILS are still the backbone of instrument approaches – and the backup when satellites fail.

1. Radio waves and range

• VOR, DME, ILS and VHF radio travel in straight lines (line of sight): mountains block them and range grows with height.
• Maximum range in NM ≈ 1.23 × (√ station height in ft + √ aircraft height in ft). At 5,000 ft over flat ground you can receive a ground station about 87 NM away; at FL350, over 230 NM.
• Low-frequency NDB signals follow the curve of the Earth and reach further, but are less accurate.

Aid	Band	Frequencies
NDB	LF / MF	190–1,750 kHz
VOR	VHF	108.00–117.95 MHz
ILS localiser	VHF	108.10–111.95 MHz (odd tenths)
ILS glideslope	UHF	329–335 MHz (paired automatically with the localiser)
DME	UHF	962–1,213 MHz (paired with a VOR or ILS frequency)

Always identify a navaid by listening to its Morse code before using it.

2. VOR

A VOR (VHF omnidirectional range) sends out 360 radials, each one a magnetic bearing from the station. Radial 090 runs east from the station.

• Set the course on the OBS (omni bearing selector). The CDI needle shows whether you are left or right of that course; each dot is about 2°, full deflection about 10°.
• The TO / FROM flag shows whether the selected course takes you towards or away from the station.
• To fly to the station on the 090 radial (which runs east), set course 270 with a TO flag. To fly outbound along the 090 radial, set 090 with a FROM flag.
• Directly over the station there is a cone of confusion where the needle swings and the flag flickers.
• The needle shows your position, not your heading: the aircraft's heading makes no difference to the reading. Correct for wind by flying a heading that keeps the needle centred.

Accuracy is about ±5°. By the 1-in-60 rule, a 5° error is 5 NM sideways at 60 NM.

3. DME

DME (distance measuring equipment) measures the time for a signal to go to the ground station and back, and shows the distance in NM – plus ground speed and time to the station when flying straight towards or away from it.

• It measures slant range, not ground distance. The difference is large only when close and high: over the station at 6,000 ft, the DME reads about 1 NM.
• A VOR radial plus a DME distance gives an exact position fix, e.g. "the 300 radial at 15 DME".

4. NDB and ADF

An NDB (non-directional beacon) transmits in all directions; the aircraft's ADF needle points to it. The needle shows the relative bearing – the angle from the nose to the beacon.

Magnetic bearing to the station (QDM) = magnetic heading + relative bearing. Example: heading 040°, needle pointing 30° right of the nose – QDM is 070°.

NDB errors: night effect (sky waves around dawn and dusk), coastal refraction (bending at coastlines), thunderstorms (the needle points to lightning) and mountains. Many NDBs are being withdrawn.

5. Bearings and Q codes

Code	Meaning
QDM	Magnetic bearing to the station
QDR	Magnetic bearing from the station (= the VOR radial you are on)
QUJ	True bearing to the station
QTE	True bearing from the station

QDM and QDR always differ by 180°.

6. ILS

The instrument landing system gives a precise path to the runway:

• The localiser shows left and right of the runway centreline – about four times more sensitive than a VOR (full deflection about 2.5°).
• The glideslope shows above and below the descent path, usually 3° – about 300 ft of height for every NM from the touchdown point.
• Marker beacons or DME distances confirm your position on the approach.
• The approach is flown down to the decision altitude: if the runway is not in sight, go around.

Rule of thumb for the rate of descent on a 3° slope: ground speed × 5 ft/min – 140 kt needs about 700 ft/min.

7. GNSS and RNAV

• GNSS (GPS, Galileo, GLONASS, BeiDou) calculates position from the time signals of several satellites. At least 4 satellites are needed for a 3D position, 5 for integrity monitoring (RAIM).
• RNAV lets you fly between any waypoints instead of from beacon to beacon; RNP adds on-board monitoring of accuracy, allowing RNP approaches.
• Positions use the WGS-84 datum.
• GNSS can be jammed or spoofed – something pilots in the Middle East meet often. Cross-check with VOR/DME and be ready to navigate without it.

8. Radar and transponders

• Primary radar sees any object by its reflection – no help from the aircraft needed, but no identity or altitude.
• Secondary surveillance radar (SSR) interrogates the aircraft's transponder: Mode A replies with the 4-digit squawk code, Mode C adds pressure altitude, Mode S adds the aircraft address and more data. ADS-B broadcasts the GNSS position continuously.
• When ATC says "squawk ident", press the IDENT button once.

Flying it at Levant

Even with an FMS, set up the raw data: tune the ILS and the VOR/DME for your arrival and check them against the FMS on approach. When an approach has an ILS, fly it on the ILS; when it is an RNAV or VOR approach, monitor the needles. In the simulator, try a flight with the GPS failed – navigating Amman to Beirut on VORs alone is good practice.

Check yourself

1. A VOR radial is a bearing to or from the station? From the station, magnetic.
2. You are on the 135 radial and want to fly to the station. What course do you set? 315 with a TO flag.
3. Heading 300°, ADF needle 040° right of the nose. What is the QDM? 340°.
4. Directly above a DME station at 12,000 ft, what does the DME show? About 2 NM (slant range).
5. Ground speed 130 kt on a 3° glideslope. Rate of descent? About 650 ft/min.

Simulation training material based on standard PPL radio navigation theory. Always use current charts and navaid information.