Study Guide:Radio Telephony

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About this Document

This document ist part of the VACC Austria Study Guide, intended to assist VACC controllers in learning their "hob" (actually: their hobby). This page is an addition to the Study Guide:OBS and covers the rules and procedures on how to speak on the radio. We assume that you have read and understood the Study Guide:OBS before. The information is based on the [CAP413 Radio Telephony Manual] of the British CAA, which is a very thorough (260pages!) document. This page is more like a tutorial: step-by-step, and only covers the basics.

Why is this?

Talking on the air is (sometimes) stressy. Voice quality may be bad or broken, but yet: it is the only link between ATC and aircraft, and therefore: highly security sensitive. You want to make sure that...

  • Communication is short
  • Communication is unambiguous ("what did he mean?")
  • Communication is fail-proof in three respects: right person, right message, right meaning.

To achieve this, people have invented something, called phraseology. Almost 99% of all radio communication is standard messages. If all the standard messages are predefined, then both sides instantly know, what they are talking about, and the non-standard communication (in "normal words") is down to an absolute minimum. Therefore, we learn this phraseology.

(Example: ATC orders "Austrian 251, turn left heading four-zero". Then it is vital that...

  • the person is right: Austrian 251 turns, not Austrian 215.
  • the message is right: It's 40 degrees, not 14.
  • the meaning is right: It's the compass degree to point the nose at (abouth northwest), not the relative angle from the present heading.

Basic Rules

In order to achieve the goals set above the following rules important:

Listen before you talk

If two people talk on the radio at the same time, they don't hear each other, and all others only hear a nasty squeak. Therefore it's important that every station monitors the frequency for about 5 seconds before transmitting, to make sure there’s no ongoing radio traffic. If you hear an ongoing conversation, wait until the conversation is over before you begin to transmit. Don’t start your communication if there is a read-back expected on the last transmission even if there is a short pause.

Think before you talk

The radio traffic flow should be as smooth as possible. To achieve this it's vital to "think first" before transmitting so that a clear, concise and uninterrupted message can be sent.

Letters and numbers are spelled

  • On the Radio, it is impossible to distinguish a "B" from a "D". Therefore, letter combinations (like callsigns, see below) are spelled. In the air, we use the NATO alphabet: Buchstabiertabelle.
  • Same is with numbers. It is difficult to distinguish "60" from "16", so numbers are read out as single digits: "six-zero" and "one-six".
  • "9" is "niner" to distinguish it from "five".
  • Decimal reads "decimal".
  • For "00" you should say "hundred" (but not for compass headings: you spell out "zero-zero")
  • For "000" you say "thousand".
  • One exception is "ten thousand" for 10 000.
  • There are very few exceptions for abbreviations which are used frequently, like VFR, IFR, VOR, NDB, ILS, RVR or VMC. An example:
ATC to A-HBU: Alpha Hotel Bravo Uniform, Radar identified at five thousand feet. Climb and maintain flight level one two zero. 
ATC to A-HBU: Alpha Hotel Bravo Uniform, direct Lima November Zulu NDB, contact Wien Radar one three four decimal three five, bye!

Stations have callsigns

You want to make sure everyone is well identified. Therefore, every participant on the network has his own Callsign. Controller Positions are identified by their location and their Function (e.g. Wien Radar, Graz Tower), Aircraft either ...

  • by their Registration (e.g. OE-ALB)
  • or an Airline Callsign followed by a combination of numbers and letters (e.g. AUA25LM, SWR387). The airline is called by its real name (i.e. "Austrian" for AUA).
  • Some letters at the end of an airline callsign mean something: "H" stands for "heavy" - an airplane from the "H" class, like the B747 or the MD81. "S" means for "super": currently only the A380. You read this class out: AUA251H is "Austrian two five one heavy". You can crosscheck these codes in the Euroscope tag, where a "/H" or "/S" is added.

Callsigns are vital, because you have to say them every time you transmit something to make sure, it is from and for the right guy.


When a controller (or aircraft) transmits a message to a station it is crucial that the receiving station acknowledge the message. But saying "roger" is only in movies - what are you "roger"ing? The called station understood something, but what? The solution is simple: The called station reads back the information in relevant parts. If the receiving station does not read back, the transmitting station must transmit again.

  • Items that must always be read back in full are all clearances (including altitudes, headings, speeds, radials etc), runway in use, altimeter setting (QNH or QFE) and transition level, and all frequencies.
  • There are also items that should not be read back to reduce unnesessary radio transmissions. In short, this includes everything not mentioned above, but a few examples are: wind, temperature and other weather information (except altimeter settings) and traffic information in detail.
LOWW_APP: AUA251, turn left heading 290, descend Altitude 5000 feet, QNH 1019.
AUA251: Turn left heading 290, descending altitude 5000 feet QNH 1019, AUA251 
LOWW_TWR: AUA251, traffic information: Cessna on rwy 16 downwind, report in sight.
AUA251: Traffic in sight, AUA251.

LOWW_GND: OE-DLT, taxi to Holding Point Runway 29 via Exit 12, M and A1, QNH 1019, give way
to Speedbird Airbus A320 crossing you right to left on M.
OE-DLT: Taxiing to H/P Rwy 29 via Exit 12, M and A1, giving way on M, QNH 1019, OE-DLT.

A note on being polite

In real life, ATC conversation is as dry as it could be - manuals say "avoid excessive courtesy". However, VATSIM is a hobby - it really depends on the circumstances. These are some guidelines:

  • It is always nice to be polite. You might say "hello" on contact and "bye" on handover. You might say "thanks for cooperation" or "sorry for the delay" if a pilot has to wait or hold or something. Some experienced controllers have found their way to be funny and make jokes in a very short manner, even if it is not VATSIM standard and should not be - VATSIM is as-real-as-it-gets compared to IVAO (xxx_APP: Lepizig Air 2134, direct UNKUL, sorry, the name was not my idea")
  • Adapt to the traffic. If you have 20 aircraft to track and the radio is full of messages, be short.
  • Don't just swallow it, if a pilot swears on you - under no circumstances he/she should. Instead of swearing back, remind him to stop and be polite, and ...
  • Don't be angry on the radio - it's not the right medium to swear, whatever a pilot (or a controller) screws up. If you really have a problem, then post a .wallop note to call for a supervisor. If you want to tell something to a pilot to explain a situation, then do so after the storm is cleared, in a private note. Even there, stay polite - you don't know why the pilot did it - maybe he can't, maybe his kid hammered on his keyboard, the joystick is faulty, the cat grabbed the chart, whatever.

Contact - messages - handover

All conversation follows the following pattern:

  1. Contact
  2. ... messages (there may be pauses, and other messages to other stations)
  3. handoff/handover.


Radio communication is like talking to each other in a dark room: You have to say hello, who you are, and that you are here now. As ATC is always there, but pilots fly in and out, it is pilots who say hello. To initiate the contact between two stations an initial call has to be made. Example - Austrian 251 is calling Wien Tower:

AUA251: Wien Delivery, Austrian 251, Radiocheck .
LOWW_DEL: Austrian 251, Wien Delivery, read you 5 by 5.

So the syntax for contact is:

Syntax = Pilot: <ATC station>, <myself>, <message>
Syntax = ATC station: <pilot>, <myself>, <message>

Contact has standard phraseology depending on the circumstances - see the sections of the controller positions.


Once contact is established, you stay in contact, even if you don't talk to each other. This means: You know that the other station listens and will pick up conversation any time. Contact is not one-to-one: ATC has contact with all aircraft in his area, whether he talks to them or not.

In ongoing conversation, three rules apply:

  • Pilots who address ATC, say their callsign first, then the message (ATC knows: if a callsign comes up, he is meant and he knows, by whom.)
AUA251: Austrian251 requesting descent.
Syntax = Pilot: <myself>, <message>
  • ATC always addresses the called station first, and then the message (ATC only talks to pilots, so whenever an aircraft's callsign comes up, there is only one guy who could be meant).
ATC: Austrian 251, descend FL 120.
Syntax = Controller: <pilot>, <message>
  • Pilots who read back an ATC instruction, put their callsign at the end. This makes sure that the right person has understood the instruction. ATC knows: if the callsign is at the end, it was a readback - he/she just checks if it is correct and the reader is correct (imagine the wrong plane descends!). ATC interferes, if it is faulty, and a new readback should follow.
AUA251: Descending FL 130, Austrian 251.
ATC: Negative, Austrian 251, descend flight level 120.
AUA251: Descending FL 120, Austrian 251.
Syntax = Pilot: <message>, <myself>

Handover / Handoff

As said before, radio conversation is like a dark room. Like pilots enter the room and say hello, it is ATC's responsibility to let him/her go. When an aircraft leaves an ATC station's responsibility, it is handed over - noone just fades away. This is vital to ensure that no plane gets lost. It's like saying goodbye and telling the pilot, where to go next. This is called "handover".

LOWW_TWR: Austrian 251, contact Wien Radar 128.2, bye
AUA251: Contacting Wien Radar 128.2, bye.

Both partners to the conversation do something after handover: ATC klicks a flag to transfer the plane in Euroscope - the next controller sees the plane popping up in his/her responsibility. The pilot switches frequency and makes the next contact to the next controller (don't worry about the details they talk about - it comes later in the tutorial. Look, if you find the syntax):

AUA251: Wien Radar, AUA251, SITNI4C, 4000ft climbing 5000ft
LOWW_APP: AUA251, Wien Radar, identified, climb flight level 125.
AUA251: Climbing flight level 125, AUA251.

Sometimes at VATSIM, there is no controller online. Then the pilot is not handed over, but handed off - released in his/her own responsibility:

LOWW_TWR: Austrian 251, radar service terminated, monitor UNICOM 122.8, bye!
AUA251: Unicom 122.8, [thanks for the service], bye!

It is pilots' responsibility to look out for ATC while they fly. Sometimes, they forget, and controllers send them a "contactme" message via Euroscope on private message (there is a command for this). In real life, this won't happen - pilots who forget to register, are fined!

Reserved words

Some words are reserved and should only be used, if they are meant (and NOT, if they are not):

  • mayday and Pan-pan: Only use it, when you declare it.
  • takeoff and landing: Only use it, when you clear (or read back) for takeoff or to land. If you inform a pilot to wait "two minutes to t... no: you tell him/her "two minutes to departure". If you inform a pilot about "late l...", no: You inform him about "late clearance".
  • Affirm(ative) means "yes". Negative means "no". Unable means that the pilot can't do what the ATC just instructed.

What?? Who?? Aaahm??

  • Say again is the only message you can pass all the time - if you did not understand, or if you did not understand if it was for you or not (and you MUST say it if you missed something!) For ATC there are three variants: Did you miss, WHO? Did you miss WHAT? Did you miss BOTH?
ATC: Last station, callsign? (WHO?)
ATC: Austrian 251, say again? (WHAT?)
ATC: Last station, say again? (WHO AND WHAT?)


If you misspell something (like a callsign, or a heading), make it clear.

ATC: Leipzig 123, correction: Leipzig 456, turn left heading 40 degrees.
ATC: Leipzig 123, turn left, ... disregard.

(You won't say "Leipzig 123 aah 456, turn...")

Phraseology at different stations

(work in progress - stay tuned!)

Phraseology is vast. To learn them step by step, the most frequently used phraseology is collected here, grouped to stations:

Study Guide:Radio Telephony:DEL is for delivery stations

Study Guide:Radio Telephony:GND is for Ground stations

Study Guide:Radio Telephony:TWR is for Tower stations