Learn how aircraft communication and navigation radios carry voice, tune ground stations, drive cockpit indications and why reception can fail.
Aircraft communication radios transmit and receive voice or data on assigned frequencies, while navigation radios receive or exchange coded signals from ground stations to calculate bearing, course deviation or distance. In Aviation & Real-World Flying, both depend on the correct frequency, antenna, audio-panel selection and an unobstructed, serviceable radio path.
What is the difference between COM and NAV radios?
A COM radio carries messages, whereas a NAV radio converts radio signals into navigation measurements or flight guidance. They may share a control panel or display, but they use different receivers, antennas and signal-processing methods.
| System | What the aircraft does | What the pilot receives | Main limitation |
|---|---|---|---|
| VHF COM | Transmits and receives | Voice or data | Mostly line-of-sight coverage |
| VOR | Receives | Radial and course deviation | Terrain, range and station overhead |
| ILS | Receives | Localiser and glide-slope deviation | Narrow approach coverage |
| ADF/NDB | Receives | Bearing to the beacon | Electrical and atmospheric interference |
| DME | Sends interrogations and receives replies | Slant-range distance | Line of sight and station capacity |
How does an aircraft communication radio work?
A conventional civil VHF COM radio is a transceiver operating on aviation voice channels from roughly 118.000 to 136.975 MHz. The transmitter places speech onto an amplitude-modulated carrier; the receiver selects that channel, extracts the audio and sends it through the aircraft's audio panel to the crew's headsets or speaker.
VHF aviation voice is normally simplex: everyone on the frequency shares one channel, and only one person should transmit at a time. Pressing the push-to-talk switch changes the selected COM unit from receiving to transmitting. Simultaneous calls can block each other or produce a squeal or garbled transmission.
Most installations provide active and standby frequency windows. The pilot enters a new frequency in standby, then transfers it to active. The audio panel separately determines which radios are heard and which COM radio will transmit, so tuning COM2 does not necessarily mean the crew is listening or transmitting on COM2.
Controllers assign frequencies for clearance delivery, ground, tower, approach, area control and other services. Our explanation of how ATC uses frequencies for clearances and traffic information covers the operational side of those conversations.
Why does COM radio range change with altitude?
VHF communication is primarily line of sight, so higher aircraft can usually contact stations at greater distances. Terrain, buildings, the Earth's curvature, antenna position and transmitter power all affect reception; hearing a distant controller does not guarantee that controller can hear the aircraft equally well.
Channel spacing also varies by region and airspace. Equipment may support 25 kHz or 8.33 kHz channels, and an 8.33 kHz display can show a channel designator rather than the carrier frequency itself. Pilots enter the published value directly rather than trying to convert it.
Long-range operations may use HF, satellite communication or data link when VHF coverage is unavailable. Those systems use different propagation and equipment, although they can still be selected through an integrated communications panel.
How do aircraft navigation radios find direction and distance?
Each navigation aid encodes a particular measurement into its radio signal, and the aircraft receiver converts that information into needles, flags, distances or flight-director commands.
- VOR: the receiver compares the phase of reference and variable signals to determine the aircraft's radial, which is a bearing from the station. The selected OBS course and TO/FROM logic then drive the course-deviation indicator.
- ILS: the localiser receiver compares overlapping 90 Hz and 150 Hz modulation patterns to show left-right deviation from the runway centreline. A paired glide-slope receiver uses the same principle for vertical guidance.
- ADF/NDB: directional antennas determine the bearing to a non-directional beacon. The indication may be relative bearing or magnetic bearing, depending on the cockpit instrument.
- DME: the airborne unit sends interrogation pulses to a ground transponder and measures the reply time. The result is slant-range distance, not horizontal or along-track distance, so it can read roughly the aircraft's height in nautical miles when directly above the station.
VOR, ILS and NDB reception is passive, but DME is a two-way ranging system. In many installations, tuning a VOR or ILS frequency automatically pairs the associated DME channel. Our broader guide explains how radio and satellite sensors feed cockpit navigation guidance.
How do pilots tune and use aircraft radios?
Pilots tune the published frequency, select the correct audio and display source, identify the station and then cross-check the resulting indication.
- Obtain the frequency. Use the applicable chart, procedure, clearance or onboard database rather than relying on memory.
- Tune and transfer it. Enter the value in standby and move it to active, or select it through the integrated avionics controls.
- Set the audio panel. Choose the COM transmitter and the receivers to monitor. Adjust volume and squelch where those controls are available.
- Identify a navigation station. Listen for its Morse-code or voice identifier and reject the indication if the identifier is absent, incorrect or accompanied by a warning flag.
- Select the display source. Set the CDI or HSI to the required VOR/localiser receiver rather than GPS, then enter the required course where applicable.
- Cross-check the result. Confirm that the bearing, deviation, distance and expected station position make sense before using them for navigation.
A mistake we see constantly in simulators is a correctly tuned NAV frequency paired with the wrong GPS/VLOC source. For hands-on examples, see our walkthrough of practical VOR and NDB tuning and interpretation.
Why is the radio tuned correctly but not working?
A correct frequency is only one part of the radio setup; power, audio routing, coverage, identification and display-source selection must also be correct.
| Symptom | Likely causes | What to check |
|---|---|---|
| No COM audio | Frequency still in standby, receiver not selected, low volume, excessive squelch or out of range | Active window, audio panel, volume, squelch and station coverage |
| ATC is heard but cannot hear the aircraft | Wrong transmitter selected, microphone or push-to-talk fault, weak transmission or simultaneous call | COM transmit selector, transmit indication, headset plug and microphone |
| NAV needle is flagged or stationary | Station out of range, wrong frequency, failed identification or wrong display source | Identifier, reception flags, NAV1/NAV2 selection and GPS/VLOC mode |
| VOR indication changes rapidly overhead | Cone of confusion above the station | Use another navigation source until clear of the station |
| DME distance seems too high nearby | Slant range rather than ground distance | Compare altitude and horizontal position relative to the station |
| ILS guidance appears reversed or implausible | Wrong localiser, back-course operation or interception outside reliable coverage | Identifier, published inbound course, approach direction and warning flags |
Electrical power matters as well. A lit flight display does not prove that every radio or audio unit has power; avionics buses, radio switches and circuit protection can be separate. Antenna or coaxial-cable faults may also affect one COM or NAV unit while the other remains usable.
Do GPS and the FMS replace navigation radios?
GPS and an FMS can reduce dependence on ground-based navigation radios, but they do not automatically replace them. GNSS calculates position from satellite signals, while an FMS combines position sources, stored routes and performance data to generate guidance.
A conventional ILS still requires the appropriate localiser and glide-slope receivers. Transport-category avionics may tune those receivers automatically, but the underlying radio guidance remains the same. The procedure, aircraft approval and installed equipment determine whether the crew uses radio-based or satellite-based guidance; our comparison of ILS radio beams and RNAV-computed approaches explains that choice.
What changes in a flight simulator?
The operating principles are the same in a flight simulator, but the depth of radio modelling varies by simulator and aircraft add-on. Coverage may be simplified, an aircraft may use custom avionics, and the simulator's navigation database may not match the chart being followed.
If a simulated station cannot be received, first check avionics power, active frequency, audio selection, range and GPS/VLOC source. Then confirm that the beacon exists in the simulator's navigation data; placing a visible antenna in scenery does not necessarily create a working radio aid.