Skip to content
FIS Book
ATM

Air Traffic ManagementLesson 2 of 5

Back to subjects
ATM 002

Radiotelephony

One frequency, shared by everyone on it

Radiotelephony is speech used as a piece of safety equipment. What makes it different from talking is not the words: it is the channel.

The working assumptionEverything you say, everybody hears 118.100MHz

A frequency is one channel with many stations on it, and only one of them can use it at a time. Every second you spend on it is a second nobody else has, and there is no way to take a transmission back.

One at a timeListeningListeningTransmittingEveryone on the frequency hears itTwo at onceTransmittingTransmittingHears neitherBoth calls are lost, and nobody knows it
Only one station can transmit at a time. Two at once cancel each other out, and neither of them finds out.
It is sharedEvery aircraft and every ground station on the frequency hears every word. A long call is a queue behind it.
It is one at a timeTwo stations transmitting together block each other. The ground station hears a squeal, or silence.
There is nothing to readNo face, no gesture, no second look. The words are the whole message.

The band you are talking on

Which frequencies air-ground speech uses, and why the number you read out is not quite a frequency.

121.500 emergency118.000122126130134136.975One 25 kHz channel is three 8.33 kHz channels118.000118.005118.010118.01525 kHz8.33 kHz each
8.33 kHz spacing did not widen the band. It cut the same band into three times as many channels.
118.000 to 136.975 MHzThe part of the aeronautical mobile VHF band used for talking to aircraft.
121.500 MHzThe aeronautical emergency frequency. Kept clear, and the one to try when nothing else answers.
8.33 kHz spacingThree channels where 25 kHz spacing gave one, so the band holds three times as many ground stations.

A channel such as 118.005 is a name rather than the frequency the set tunes to. It is read out digit by digit like any other.

The language

Radiotelephony has a language of its own, and it is not quite English.

English, or the language the ground station normally uses.That is the rule, in ICAO Annex 10 and SERA.14015, and it binds. English must be available on request wherever international traffic is served, and it is required at aerodromes with more than 50 000 international IFR movements a year. Everywhere else it is strongly advised, so that everyone on the frequency can follow what is happening. Danish stations work in Danish and English.
A standardised form of EnglishUsed in aviation, with a vocabulary, a grammar and a pronunciation of its own.
A fixed set of words and phrasesUniversally understood and accepted, so the same words mean the same thing on every frequency.
Simple and concise on purposeGrammatically structured that way to minimise misunderstandings.
English is borrowedFor most people on the frequency it is a second language. A phrase you improvised is a phrase they have never heard.
Standard phraseology is used in every situation it has been written for.Plain language is for the situations it has not. That is the order: the standard phrase first, your own words only when there is no standard phrase.

Before you press

A transmission starts before the switch does. Two of these five happen before the switch is even pressed.

Step 1 ListenCheck the frequency is actually free. Somebody may be halfway through a clearance.
Step 2 ThinkHave the whole message ready. Working it out on air spends everybody’s frequency.
Step 3 PressPush the transmit switch fully home, and let a beat pass before the first word.
Step 4 SpeakEven rate, steady volume, microphone at a constant distance.
Step 5 ReleaseOnly once the message is finished, so the last word is not cut off.
Pressing late, releasing early118.100
OY-BHK COPENHAGEN INFORMATION, OY-BHK, REQUEST FLIGHT INFORMATION

The switch was pressed while the first word was already being said, and released on the last one. Both ends of the message are gone.

Copenhagen Information STATION CALLING COPENHAGEN INFORMATION, SAY AGAIN

Two transmissions spent, and the frequency is no further forward.

What it costsA clipped call is not a small error. It is the whole exchange again, on a frequency somebody else was waiting for.

How to speak

Eleven items, lettered the way the course letters them. Teal is about the frequency, blue about the voice, purple about the microphone, amber about being understood.

050100150200100WORDS PER MINUTE, AND NO FASTEREven, and unhurriedFaster than it can be written
A 25-word read back at 100 words a minute takes 15 seconds. Faster than that and the other end stops being able to write it down.
Listen out first

Before transmitting, listen out on the frequency to be used to ensure that there will be no interference with a transmission from another station.

Know your microphone

Be familiar with good microphone operating techniques.

Normal tone, clear words

Use a normal conversational tone, and speak clearly and distinctly.

Not above 100 words a minute

Maintain an even rate of speech not exceeding 100 words per minute. When it is known that elements of the message will be written down by the recipient, speak at a slightly slower rate.

Constant volume

Maintain the speaking volume at a constant level.

Pause around numbers

A slight pause before and after numbers will assist in making them easier to understand.

No hesitation sounds

Avoid using hesitation sounds such as “er”.

Constant distance from it

Be familiar with the microphone operating techniques, particularly in relation to the maintenance of a constant distance from the microphone if a modulator with a constant level is not used.

Turn away, stop talking

Suspend speech temporarily if it becomes necessary to turn the head away from the microphone.

Press fully, release late

Depress the transmit switch fully before speaking and do not release it until the message is completed. This will ensure that the entire message is transmitted.

Break up a long message

The transmission of long messages should be interrupted momentarily from time to time to permit the transmitting operator to confirm that the frequency in use is clear and, if necessary, to permit the receiving operator to request repetition of parts not received.

Compose the message before you send it.Clear, concise, and with the unnecessary words already taken out. Written messages are read through before they are transmitted, and a spoken one deserves the same.

Good radio, and bad

Four qualities, each one sitting opposite the fault it is the absence of.

Good radioBad radio
TimelySaid at the moment it is worth saying.
Slow, or lateThe moment for it has gone.
PreciseSays one thing, and says it exactly.
SloppyLeaves the other end to guess which of two things was meant.
ConciseNo word in it that is not doing work.
Long-windedPadded out with extraneous verbiage.
DisciplinedIn the standard form, in the standard order.
DisorganisedFilled with pauses, and worked out while the switch is held down.
Good radio work is the hallmark of a proficient, intelligent and professional operator.

What a call is made of

Three pieces, always in the same order. It is the same shape whether the call is the first of the flight or the twentieth.

COPENHAGEN INFORMATIONOY-BHKREQUEST FLIGHT INFORMATIONWho you are callingThe place, then the stationWho you areYour callsignWhat you wantOne thing, as short as it goesAlways this order. A station will not listen properlyuntil it knows the call is meant for it.
Who you are calling, who you are, what you want. The station has to recognise its own name before it will listen to the rest.
Establishing contact118.100
OY-BHK COPENHAGEN INFORMATION, OY-BHK
Copenhagen Information OY-BHK, COPENHAGEN INFORMATION, PASS YOUR MESSAGE
OY-BHK OY-BHK, CESSNA 172, ROSKILDE TO ODENSE, PASSING 2 000 FEET, REQUEST FLIGHT INFORMATION

The full message comes second, once the unit has said it is listening. Calling and delivering in one breath risks having to say all of it again.

Abbreviating a callsign

A callsign may be shortened once the two stations are hearing each other properly and there is nothing else on frequency it could be confused with. The three callsign types themselves are in LAW 003.

The ground station goes firstAn aircraft uses the short form only after it has been addressed that way. It never shortens its own callsign on its own initiative.
Type (a), the registrationThe first letter, then at least the last two. OY-BHK becomes “O-HK”. The forms are in LAW 003.
Type (b), operator and registrationThe telephony designator, then at least the last two characters. “Dancopter Yankee Hotel Mike Uniform” becomes “Dancopter Mike Uniform”.
Type (c), operator and flight identificationNo abbreviated form exists. A flight number is said in full, every time.
Similar callsigns are never abbreviated. Two aircraft on frequency ending in the same two characters is exactly the case the rule is guarding against, and it is the ground station’s job to notice it first.

Standard words and phrases

Each of these has one meaning and only one. That is the whole reason they exist: a word that could mean two things is not doing the job.

Learn by heart

In test mode the answers are hidden. Click or tap a card to reveal it.

AFFIRM Yes.
NEGATIVE No, or that is not correct, or permission is not granted, or not capable.Also the word for putting right a wrong read back.
ROGER I have received all of your last transmission.Nothing more than that.
WILCO I have heard and understood what you have said, and I will do as instructed.Short for will comply.
CORRECT True, or accurate.Used to confirm that a read back was right.
UNABLE I cannot comply with that, or I cannot authorise it.Used by pilots and by the operator.
STANDBY Wait, and I will call you.
CONFIRM I request verification of a fact or a detail.
REQUEST I am asking for information, or for authorisation.
SAY AGAIN Repeat all, or the following part, of your last transmission.
SPEAK SLOWER Reduce your rate of speech.
HOW DO YOU READ What is the readability of my transmission?
WORDS TWICE Send every word, or group of words, twice.For exceptionally bad reception only: it doubles the time on frequency.
REPORT Pass me the following information.
ACKNOWLEDGE Let me know that you have received and understood this message.
CHECK Examine a system or a procedure.No answer is normally expected.
CLEARED Authorised to proceed under the conditions specified.
APPROVED Permission for the proposed action is granted.
MAINTAIN Stay at that level, or on that frequency.A pilot also uses it to state a level.
CONTACT Change to the new frequency and call them.
MONITOR Listen out on a frequency.Listen. Do not call.
RECLEARED A new clearance, replacing the one already given.
CANCEL Annul the clearance already transmitted.
DISREGARD Ignore the message already sent.
READ BACK Read that back to me.Only needed when a pilot has not read back unprompted.
CORRECTION I have made an error. The correct version is.
I SAY AGAIN I repeat, for emphasis or for clarity.
BREAK I am separating parts of the same message.Without leaving space on the frequency.
BREAK BREAK I am separating messages to different aircraft.Without leaving space for a read back or any other transmission.
ALL STATIONS This is a broadcast, not a call to any one station.Prefaces a broadcast from the ground or from an aircraft.
Good to know

Not on the course list. Both are standard ICAO words and neither is normally used on VHF, because releasing the switch already says the transmission has ended. Never “over and out”: the two mean opposite things.

In test mode the answers are hidden. Click or tap a card to reveal it.

OVER My transmission is ended and I expect a response from you.
OUT This exchange is ended and no response is expected.
The three that get misused
The commonest mistake ROGER is not an answer ROGER
For information you have received and have nothing to say back to
Never in reply to a question
Never where a read back is required
Not a decision STANDBY grants nothing STANDBY
It means: wait, I will call you
It is neither an approval nor a refusal
Acting on it as though it were a clearance is the trap
One word apart in meaning WILCO is ROGER plus a promise WILCO

I have heard it, I have understood it, and I will do as instructed.

ROGERSays only that the transmission arrived. It promises nothing.

WILCOSays it arrived, that it was understood, and that it will be complied with.

Two for a busy frequency

Both are in the grid above. They are here as well because they share one reason, which a card on its own cannot carry: an operator can keep going without leaving a gap that somebody else would transmit into.

One messageBREAK

Separates portions of the same message, without stopping to leave any space on the frequency.

Two messagesBREAK BREAK

Separates messages to different aircraft, without leaving space on the frequency for a read back or any other transmission.

Reading back

The read back is the only check the system has that a message arrived intact. It is not politeness, and it is not optional.

Always read back
Route clearancesThe whole clearance, as issued.
Level instructions
Heading and speed instructions
Altimeter settings
SSR codes
Transition levelsHowever they reach you, from the controller or from an ATIS broadcast.
Newly assigned communication channels
Runway in use
Runway instructionsEnter, land on, take off from, hold short of, cross, taxi and backtrack. Every one of them.
A read back ends with the callsign.Without it the controller has heard the right words from an unknown aircraft, which is not a check at all.
A read back, and a correction118.100
Copenhagen Information OY-BHK, QNH 1008, TRANSITION LEVEL 55
OY-BHK QNH 1080, TRANSITION LEVEL 55, OY-BHK

Two digits swapped. This is the moment the read back exists for.

Copenhagen Information OY-BHK, NEGATIVE, I SAY AGAIN, QNH 1008
OY-BHK QNH 1008, OY-BHK

What the read back is forTwo digits swapped, and caught inside one exchange. Without the read back the aircraft flies on the wrong setting and nobody finds out.

Putting it right, and asking again

Three procedures that exist because speech goes wrong: your own error, an error you did not catch, and a message meant for everybody.

When you make an error
Part of the messageSay CORRECTION, repeat the last correct group or phrase, then give the correct version.
The whole messageWhere repeating all of it is the clearest fix, say CORRECTION, I SAY AGAIN, then send the whole message once more, correctly.
Correcting part of a message118.100
Copenhagen Information OY-BHK, TRAFFIC 2 O’CLOCK, 5 MILES, CORRECTION, TRAFFIC 3 O’CLOCK, 5 MILES

CORRECTION, then the last correct group again, then the right version. Nothing before that group is said twice.

For the whole messageCORRECTION, I SAY AGAIN, then the message a second time, correct this time. The corrected message is said once, not twice, which is how the course’s written form, C/S, CORRECTION (correct message), I SAY AGAIN (correct message), can read.

When somebody else gets it wrong
Start with NEGATIVECORRECTION is for putting right your own transmission. Correcting what somebody else read back starts with NEGATIVE, then I SAY AGAIN and the right version.
When the message may not get through
An uncertain callsignWhere it is not certain who is calling, the calling station is asked to repeat its callsign until the identity is established.
Poor reception expectedWhen reception is likely to be difficult, the station transmitting should say the important elements of the message twice, without being asked. ICAO recommends it; it is not a rule. SAY AGAIN belongs to the other end: it is what the receiving station says when something did not get through.
Talking to everybody at once

The card above gives the meaning. These are the two times it is used. The prefix is the same in both directions, and it tells everyone to listen without waiting to hear their own callsign.

From the groundALL STATIONS

When a ground station wishes to broadcast information, the message is prefaced by the call ALL STATIONS.

From the airALL STATIONS

When an aircraft wishes to broadcast information to aircraft in the vicinity, the message is prefaced by the same call.

Saying numbers

Numbers are said digit by digit, except where one of the rules below says otherwise. Which rule applies depends on what the number is. The rule itself, and the ICAO alphabet, are in LAW 003.

Never hundredsHeadings and wind: every digit, even when the number is a whole hundred.
  • Heading100“HEADING ONE ZERO ZERO”
  • Wind200/70“WIND TWO ZERO ZERO DEGREES SEVEN ZERO KNOTS”
Whole hundredsFlight levels and speeds: a whole hundred is said as HUNDRED. Anything else, digit by digit.
  • Flight levelFL 180“FLIGHT LEVEL ONE EIGHT ZERO”
  • Flight levelFL 200“FLIGHT LEVEL TWO HUNDRED”
  • Speed250 kt“TWO FIVE ZERO KNOTS”
  • Speed300 kt“THREE HUNDRED KNOTS”
Whole thousandsQNH and transponder codes: only a whole thousand is said as THOUSAND. For QNH, that is 1000 hPa alone.
  • QNH1008“QNH ONE ZERO ZERO EIGHT”
  • QNH1000“QNH ONE THOUSAND”
  • Squawk2400“SQUAWK TWO FOUR ZERO ZERO”
  • Squawk4000“SQUAWK FOUR THOUSAND”
Mix of the twoAltitude and visibility: thousands and whole hundreds, said together.
  • Altitude2 500 ft“TWO THOUSAND FIVE HUNDRED FEET”
  • Altitude10 000 ft“ONE ZERO THOUSAND FEET”The ten is still two separate digits.
  • Visibility1 500 m“VISIBILITY ONE THOUSAND FIVE HUNDRED METRES”
Decimals and timeThe point is said as DECIMAL. A time is normally the minutes alone.
  • Channel118.105“ONE ONE EIGHT DECIMAL ONE ZERO FIVE”
  • Time0920“TWO ZERO”, or “ZERO NINE TWO ZERO”The hour goes in as well wherever it could be mistaken.
Europe differs from ICAO here. These rules are SERA.14035, which is binding law in Denmark. ICAO Annex 10 has flight levels, speeds, QNH and squawks said digit by digit, such as “FLIGHT LEVEL TWO ZERO ZERO” and “QNH ONE ZERO ZERO ZERO”, and keeps hundreds and thousands for altitude, cloud height, visibility and RVR. Annex 10’s rule is a Standard, so Denmark has notified the European version to ICAO as a difference, listed in AIP Denmark GEN 1.7.

The pause is part of the rule. A slight pause before and after a group of digits is what lets the other end write them down. Without it, “one zero zero zero” is just a noise.

Radio check

Asking how you are being heard, and answering it. The answer is a number from one to five.

  1. The station you are callingWho the check is addressed to.
  2. Your callsignWho is asking.
  3. RADIO CHECKThe standard phrase.
  4. The frequency in useWhich channel is being checked.
1
UnreadableNothing usable is getting through.
2
Readable now and thenWords arrive, the message does not.
3
Readable but with difficultyIt works, and it is costing both ends effort.
4
ReadableGetting through without effort.
5
Perfectly readableLoud and clear.
A radio check118.100
OY-BHK COPENHAGEN INFORMATION, OY-BHK, RADIO CHECK 118.100
Copenhagen Information OY-BHK, COPENHAGEN INFORMATION, READABILITY FIVE

The other way roundHOW DO YOU READ asks the same question in the middle of an exchange, when a full radio check would be more than is needed.

When you cannot get through

Two phrases for the case where you are not sure anybody can hear you.

You can still receiveTRANSMITTING BLIND

Sent when you cannot establish contact but believe your transmissions are still getting out. The message is sent twice, prefixed with the phrase.

You cannot receive eitherTRANSMITTING BLIND DUE TO RECEIVER FAILURE

The same, with the reason added, so the ground station stops waiting for an answer that cannot come. Say when the next transmission is due.

A radio failure is also squawked, on the transponder code set aside for it.

Which message goes first

When more than one thing needs saying on a frequency, the order is fixed. It is not first come, first served.

On a frequency
  • 1
    DistressSerious and imminent danger, requiring immediate assistance.
    MAYDAY
  • 2
    UrgencyThe safety of the aircraft, or of a person on board or within sight, but not requiring immediate assistance.
    PAN PAN
  • 3
    Direction findingCommunications to do with finding an aircraft’s bearing or position by radio.
  • 4
    Flight safetyMovement and control messages, position reports, and anything else bearing on the safety of a flight.
  • 5
    MeteorologicalWeather for a flight, whether it is on the ground or in the air.
  • 6
    Flight regularityServicing, schedule changes, non-routine landings and the arrangements around them.

Everything below a distress or urgency call waits, including anything already halfway through being said.

These six are the order on a frequency, from Annex 10. They are not the five AFTN priority codes in LAW 007, which order written messages on the network. Three of the names appear in both lists, at different numbers.

Distress and urgency

The two calls that take the frequency over. What each one means, and the signals themselves, are in LAW 005; this is how they are said.

DistressMAYDAY
MAYDAYMAYDAYMAYDAY

Preferably said three times. Serious and imminent danger, requiring immediate assistance.

UrgencyPAN PAN
PAN PANPAN PANPAN PAN

Preferably said three times. A condition concerning the safety of the aircraft, or of a person on board or within sight, but not requiring immediate assistance.

What goes in the message, in order
  1. The station addressed

    Time and circumstances permitting. If there is no time, the call goes out anyway.

  2. The aircraft identification
  3. The nature of the condition

    What has happened.

  4. The intention of the person in command

    What the aircraft is going to do about it.

  5. Present position, level and heading

    Where to look.

A distress call118.100
OY-BHK MAYDAY MAYDAY MAYDAY, COPENHAGEN INFORMATION, OY-BHK, ENGINE FAILURE, FORCED LANDING, 15 MILES SOUTH OF ODENSE, 2 000 FEET, HEADING 180
Copenhagen Information OY-BHK, COPENHAGEN INFORMATION, ROGER MAYDAY
Copenhagen Information ALL STATIONS, COPENHAGEN INFORMATION, STOP TRANSMITTING, MAYDAY

Silence can be imposed on the frequency by the aircraft in distress or by the station handling the distress traffic.

Copenhagen Information ALL STATIONS, COPENHAGEN INFORMATION, DISTRESS TRAFFIC ENDED, OUT

The frequency is not free again until somebody says so.

The five pieces are in thereStation, identification, nature, intention, and position with level and heading. Said in that order, and said once.

121.500 MHz is the aeronautical emergency frequency, and is the one to try when the frequency in use brings no answer.

Best practice, in one place

Nothing here is new. It is the same lesson said as habits.

Listen before you press

Somebody may be halfway through a clearance you are about to erase.

Do not think out loud on frequency

Work the message out first. Hesitation costs everybody.

One call, one subject

Three requests in one transmission come back as three questions.

Do not invent a phrase

If a standard word exists, it is the right one, however ordinary it sounds.

Read back what must be read back

With your callsign on the end of it.

Do not answer a question with ROGER

It says the words arrived. It does not say yes.

When in doubt, ask

SAY AGAIN costs a few seconds. A wrong read back that nobody catches costs a great deal more.

Brevity is not the goal. Being understood the first time is.Short is usually how that happens, which is why the two get confused.

Reading material

Air Traffic Management

ATM 002 Radiotelephony PowerPoint / PDF
002 Radiotelephony eLearning
Commission Implementing Regulation (EU) No 923/2012 (SERA), Section 14 (Voice communication procedures) Reading list, free
International Civil Aviation Organization, Procedures for Air Navigation Services: Air Traffic Management, Doc 4444, 16th edition, 2016 Reference, paid
International Civil Aviation Organization, Doc 9432, Manual of Radiotelephony, 4th edition, 2007 Reference, paid
European Union Aviation Safety Agency, Easy Access Rules for Standardised European Rules of the Air (SERA), May 2025 Reference, free