Communication

To standardise communication, the English language is used for international radiotelephony. In certain regions, at certain airports and for certain services, the national language may be used in addition to English.

The understandability and thus also the usefulness of radiotelephony itself depend to a large extent on pronunciation.

When transmitting a letter or group of letters, such as a call sign, or when spelling a word that is difficult to understand, the ICAO phonetic alphabet shall be used.

The following abbreviations are generally not spelled according to the ICAO phonetic alphabet, but simply transcribed using the English alphabet:

VFR, VMC, IFR, IMC, QNH, QFE, RVR, CB, AIS, ATC, CTR, TMA, FIR, QDM, QDR, NDB, VOR, DME, DF, VHF, EOBT, ETA, PPR, UTC, DC-9, MD-80, MD-11

• To avoid possible confusion between FIVE and NINE, the nine is pronounced NAINER.
• For numbers containing a comma, the word «DECIMAL» is used instead of the comma.
• The number zero is pronounced ZERO and not O (letter O) as it is colloquially.
• In the entire series of numbers, each digit is pronounced individually.

Exceptions to the above rule are:

• Integer hundreds and thousands and combinations thereof when used to convey numbers relating to altitude, cloud height, visibility and RVR (see examples below). For numbers 100 or 1000, the number ONE is pronounced ONE HUNDRED and ONE THOUSAND.
• Traffic information or directions in terms of clock-reference are transmitted for example as «TEN O`CLOCK».
• The instruction to perform a full circle with the expression «MAKE A THREE SIXTY», although the expression «MAKE AN ORBIT» is more correct and unambiguous.

The communication frequencies are in the VHF frequency band. The channel band between the individual frequencies is 8.33 kHz.

If a pilot receives a frequency from air traffic control, it must be read back, even if he did not request it. To avoid misunderstandings of frequencies, all six digits must normally be read back. The exception is if the last two digits are zeros (e.g. 121.700), then only the first four digits must be read back. The decimal point is pronounced «DECIMAL».

Change to another frequency

If a pilot is instructed to change frequency, the pilot shall only repeat the frequency. All other information regarding the frequency change, such as the name of the station, shall be omitted.

Throughout the world, the same time is used in aviation, known by the following terminology:

UTC

Z-Time

Universal Time Coordinated

Z-Time ZULU TIME (is used in meteorology)

- the time zone at the prime meridian on which the Greenwich Observatory is located, also called GMT (Greenwich Mean Time).

Call Signs for Aeronautical Stations

All the air traffic that develops over a country cannot be controlled by a single ground station. For this reason, the airspace has been divided into sectors, each with its own air traffic control and monitoring centre (Flight Information Service «FIS»). Each control station operates on its own frequency and assumes responsibility for all traffic that takes place in its area within the limits of its jurisdiction. Depending on their function, these stations have a call sign composed of:

For example:

BERN TOWER

is responsible for all take-off and landing traffic at BERN airport and in the immediate vicinity (control zone) on the frequency 121.025 MHz.

ZURICH ARRIVAL

on the frequency 118.0 MHz is responsible for the separation and integration of approaching traffic according to instrument flight rules in ZURICH- KLOTEN.

Call Signs for Aeronautical Stations

When the bilateral radio link is established, mutual reception is excellent and there is no risk of confusion, the geographical designation (e.g. ZURICH, GENEVA, etc.) or the station service (e.g. TOWER, INFORMATION, etc.) may be omitted.

Call Signs for Aircraft Stations

Each aircraft entered in the official register is marked with an identification or registration mark.

• In principle, the registrations consist of five characters (letters or numbers).
• The first letter or the first two letters indicate the nationality of the aircraft.

Here are some examples of nationality designators:

D
EC
F
G
HA
HB
I
OE
OO
SX
N
T7

–
–
–
–
–
–
–
–
–
–
–
–

Germany
Spain
France
Great Britain
Hungary
Switzerland and Principality of Lichtenstein
Italy
Austria
Belgium
Greece
United States of America
San Marino

Call Signs for Aircraft Stations

A communication starts with a call and an answer, unless it is certain that the called station will hear the call. In this case, the message can proceed directly. For ground stations such as TOWER, GROUND, APRON, ARRIVAL, the aircraft can normally transmit the message immediately after contact is made without first waiting for a response from the called station. With INFORMATION and ALPS RADAR, however, one waits for a response from the called station before proceeding with the message.

The first time a call is made on a frequency, the full callsign must always be used.

Thereafter, the abbreviated callsign is used if the possibility of confusion with other callsigns is practically excluded. The aircraft shall only use the abbreviated form when called by the ground station using this form.

Once the connection is established, subsequent calls will not use the ground station callsign anymore.

To avoid possible confusion, both ATC control centres and pilots shall add the aircraft's call sign to each respective ATC clearance that is issued and repeated.

If a called station is in doubt about the calling station›s call sign, use the following expression: STATION CALLING, SAY AGAIN YOUR CALL SIGN.

Order of the information to be transmitted at the first call:

If there is a GROUND frequency and a TOWER frequency at an aerodrome, as for example in Locarno, Sion or Basel, then the destination aerodrome is reported to the GROUND under Destination and the outbound route to the TOWER.
If there is only a TOWER frequency, the destination aerodrome and the outbound route will be communicated at the first call for taxiing under Destination.

On an aerodrome with GROUND and TOWER, the ATIS identifier is only communicated to the GROUND. It is omitted from the subsequent call to the TOWER.

Order of the information to be transmitted at the first call:

Each instruction received must be read back (acknowledged) by the pilot. The way in which an instruction must be confirmed depends on its importance.

Readback (repeating the instruction word for word)

• All clearances pertaining to the runway used, alignment, landing, take-off, crossing and backtrack must be read back.
• The runway used, altimeter setting, transponder codes, altitude, heading and speed assignments must always be repeated word for word.
• A «readback» is also required when a frequency or radio bearing information is transmitted via radio.
• ATC route clearances must be repeated word for word.
• An aircraft must complete a «readback» with its callsign.

Repeat in the sense

Other clearances or instructions as well as «conditional clearances» must be confirmed or acknowledged in a way that shows that they are understood and followed.

WILCO (Will comply)

For «simple» and unambiguous instructions, such as REPORT READY FOR DEPARTURE or REPORT FINAL, the expression «WILCO» can be used.

Confirmation with «ROGER» or your own callsign

Information about weather, wind, runway conditions, work in progress, etc. does not need to be repeated, it is sufficient to confirm it briefly with your own callsign.

It is irresponsible to acknowledge receipt of a message with the word «ROGER» if it has not been understood. In this case, one must request a repeat with «SAY AGAIN....».

.

After the connection between the aircraft and the ground station is established, the callsign of the aircraft is used for further transmissions:

at the beginning of the message:

whenever the aircraft starts transmitting a message.

at the end of the message:

when the aircraft acknowledges receipt of a clearance or instruction, in other words, each «read back» is terminated with the aircraft's call sign.

When it is necessary for a station of the aeronautical mobile service to perform a readability check, these calls shall not exceed 10 seconds. For the purpose of testing a particular radio installation, the transmission shall include the following:

• identification of the station being called
• identification of the station calling
• the phrase RADIO CHECK
• the frequency being used

Readability is indicated in the following levels:

1
2
3
4
5

Unreadable
Readable now and then
Readable, but with difficulty
Readable
Perfectly readable