Understanding aviation radio frequencies: bands, services and where to find them

If you take a first look at an aerodrome chart, you see a whole column full of numbers: 118 point something, 121 point something, plus call names like Delivery, Ground, Tower and Approach. These aviation radio frequencies seem arbitrary at first glance but follow a clear logic. This guide explains how the airband is built, why the display often shows a different number than the actual transmit frequency, which services at an airport work on which channel – and where to look up the official details. One thing up front: understanding frequencies is one thing, listening in on radio traffic is another. In Germany, the latter is not allowed without authorization; more on that below and in the article Listening to aviation radio: technology and legal situation.

Aviation radio frequencies: the short answer

Civil aviation radiotelephony runs in the VHF band between 117.975 and 137 MHz, and the channels actually used range from 118.000 to 136.975 MHz. Transmission uses amplitude modulation (AM), and communication is half-duplex – one transmits, everyone else listens. Every air traffic control station that looks after an aircraft along its way has its own frequency: from the departure clearance through taxiing, takeoff and landing to en route control. The binding frequencies of an airport are in the Aeronautical Information Publication (AIP) of the respective country.

How the airband is divided

What spotters casually call the “airband” is actually a collection of several ranges. Not everything in it is radiotelephony.

Range	Frequencies	Used for	Modulation
VHF navigation	108–117.975 MHz	VOR beacons, ILS localizer transmitters	navigation signals, no radiotelephony between cockpit and controller
VHF radiotelephony	117.975–137 MHz	Tower, Ground, Approach, Radar, ATIS, data link	AM
Shortwave (HF)	approx. 2.85–22 MHz	voice and data radio over oceans and remote areas	single sideband
Military UHF	225–400 MHz	military air traffic control and military air-to-air radio	AM

The boundary at 117.975 MHz is no coincidence: below it, ground installations transmit that help aircraft navigate. A VOR shows the cockpit which course it is flying relative to the station, while an ILS localizer guides the aircraft laterally onto the runway centerline. How this works together on approach is explained in the article ILS approach explained. For the ILS glide path, by the way, the system uses a separate UHF range around 330 MHz.

Above 137 MHz, aviation radio ends – other services begin there. In the upper part of the radiotelephony band, besides voice channels there are also frequencies for data link: via ACARS and its successor, aircraft and airlines send short text messages back and forth, such as position reports or weather data. The technical side behind it is described in the article Receiving ACARS messages.

Why AM? The quirks of aviation radio

If you mostly know radio from FM, you might wonder: aviation radio sounds thin, hisses and crackles. That is due to amplitude modulation – and it was chosen deliberately.

• Intelligible despite noise: AM voice remains recognizable even with a weak signal and long distance, when an FM signal would already break up.
• No capture effect: With FM, the stronger of two simultaneous transmitters prevails and the weaker one disappears unnoticed. With AM, both overlap audibly – there is a whistle or squeal. Controller and crew thus notice that two have just transmitted at once, and ask for a repeat.
• Half-duplex: Only one station can speak on a frequency at a time. That is why phraseology is so brief and standardized: every second of airtime is missing for everyone else. More on this in the guide to radio phraseology.

It is precisely the half-duplex logic that explains why a large airport needs so many different frequencies. If all aircraft near the ground spoke on a single channel, nobody would get a word in.

25 kHz or 8.33 kHz: the channel spacing

For a long time, radiotelephony channels in the VHF band were 25 kHz apart. That gives roughly 760 channels – too few for the dense European airspace with its many sectors, airports and services. Europe therefore introduced the 8.33 kHz spacing: each 25 kHz segment is divided into three narrower channels, so in theory about three times as many channels fit into the band. The changeover began in the late 1990s in the upper airspace of the core European states, which include Germany; since then, the spacing has been extended step by step to further airspaces.

Channel name and real frequency

So that crews do not have to deal with four decimal places, in the 8.33 kHz spacing you select a channel name that only roughly corresponds to the carrier frequency. This causes confusion at first but is simple once you know the principle. For each 25 kHz block there are four channel names: one for the old wide channel and three for the narrow ones.

Channel name	Spacing	Actual carrier frequency
118.000	25 kHz	118.0000 MHz
118.005	8.33 kHz	118.0000 MHz
118.010	8.33 kHz	approx. 118.0083 MHz
118.015	8.33 kHz	approx. 118.0167 MHz

So the channel name also tells the radio which filter width to use. The same principle repeats across the whole band; a channel designated 118.025 in the 25 kHz spacing is tuned in 8.33 kHz mode as 118.030, for example. If you read a frequency with “odd” final digits such as .005, .010 or .015 on a chart or in the AIP, it is an 8.33 kHz channel. The finer points of the changeover are described in the article on the 8.33 kHz channel spacing.

Delivery, Ground, Tower, Approach: who sits on which frequency

An airline flight passes through several responsibilities from the gate to cruising altitude. At large airports, each of them has at least one frequency of its own, often several, which are combined or split depending on traffic. The typical chain looks like this:

Which station is meant is revealed by the call name: it consists of the place name and the service. Controlled airfields identify themselves with the place name plus “Tower”, and the German area control centers with a name plus “Radar”, such as “Langen Radar”. A special case is “Rhein Radar” for upper airspace control from Karlsruhe. At uncontrolled airfields, the ground radio station in Germany is called “Radio”, and at airfields with an aerodrome flight information service “Information”. The article Delivery, ground, tower, approach, center sets out the tasks side by side in more detail. Who is behind these stations in Germany is explained in the article on DFS Deutsche Flugsicherung.

Special frequencies you should know

Besides the frequencies of individual airports, there are a few channels with a defined special role.

• 121.5 MHz – emergency frequency: The international distress and calling frequency of civil aviation. It is monitored continuously by many stations. This is where crews report in who cannot reach their responsible station, for example. What “Mayday” and “Pan-Pan” mean is explained in the article Mayday and Pan-Pan.
• 243 MHz – military emergency frequency: The counterpart in the military UHF band.
• 123.45 MHz – air-to-air: Originally intended as a channel for conversations between aircraft, today it is provided only over oceans and in remote areas. In Germany there are separate air-to-air channels for this, plus regional frequencies for gliding and balloons, for example.
• ATIS and VOLMET: Automatically broadcast weather and aerodrome information. ATIS applies to one airport, while VOLMET stations broadcast weather reports for several airfields. How to understand ATIS information is shown in the article ATIS explained; the weather codes in it are the same as in METAR and TAF.

The transponder signal that flight tracker apps use, by the way, has nothing to do with these radiotelephony frequencies: it runs on 1090 MHz and carries data instead of voice – more on this in the article Transponder Mode A, C and S. The well-known emergency codes like 7700 are not frequencies either but transponder codes – see Squawk codes 7500, 7600 and 7700.

Where to find aviation radio frequencies officially

Frequencies change. New 8.33 kHz channels are assigned, sectors are redrawn, services are merged. So it pays to check at the source right away.

How to find your way around an aerodrome chart – including the frequency block, runway designations and taxiways – is explained in the guide Reading AIP aerodrome charts. An introduction to the free mapping platform is in the article on openAIP. When reading, it helps to know the airspaces, because not every airspace requires radio contact: the article on airspace classes A to G explains that.

How to read a frequency entry

A typical entry in an AIP aerodrome section consists of a few columns: the type of service (such as TWR, GND, APP, ATIS), the call name, the frequency and the operating hours. Sometimes there are additions like “as instructed” or notes on which frequency applies to which runway. Large airports like Frankfurt Airport or Munich Airport therefore have much longer lists than a regional airport: several apron and taxi areas, several runways and separate channels for arrivals and departures.

Knowing frequencies does not mean you may listen in

This is the point where many spotters stumble. The frequencies are public in the AIP, receivers for the airband are freely sold, and abroad there are even online streams. Even so, in Germany the prevailing view is that aviation radio is not a message for the general public. The ban on eavesdropping in the TDDDG allows listening only if a message is intended for you or for the general public – and also prohibits passing on or publishing what you heard. The fact that you can look up a frequency does not change that.

Buying and owning a scanner or SDR stick is allowed, so you can certainly get to grips with the technology. What the devices can do is covered in the articles Buying an aviation radio scanner and Receiving aviation radio with an SDR stick; where web streams and apps stand is clarified by Listening to aviation radio online and the comparison of aviation radio apps. Before any use, though, be sure to read the article on the legal situation of aviation radio. Anyone who wants to transmit themselves and thereby also listen legally needs a radiotelephony certificate: BZF II for VFR in German, BZF I additionally in English, AZF for instrument flight. Whether German or English is spoken on the radio is explained in the article English or German on aviation radio.

What to keep in mind

• Keep channel name and frequency apart. Technical data sheets sometimes show the real carrier frequency, while charts and the radio use the channel name. Both are right, but not the same.
• Check how current the source is. A five-year-old frequency list is hardly usable anymore in the 8.33 kHz era.
• Do not confuse navigation with voice. Everything below 118 MHz in the airband belongs to navigation aids, not to conversations with the Tower.
• Not every frequency is staffed around the clock. Many services have operating hours; at night, frequencies are often combined.
• Use legal alternatives. For the question “Which runway is active today?”, wind, METAR and live data are enough. How wind and runways are connected is shown in the guide Understanding runway direction in use at an airport.

Conclusion

Aviation radio frequencies are less cryptic than they look. Radiotelephony sits in the VHF band between 118 and 137 MHz and works in AM, with the navigation aids transmitting below it. The narrow 8.33 kHz spacing provides more channels and channel names that only roughly match the real frequency. At the airport, every phase of the flight has its own station with its own frequency – from ATIS and Delivery to Approach and Radar. You can look everything up authoritatively in the AIP. And anyone who spots in Germany understands the frequencies best without listening in on the radio traffic themselves.