RadioTelephony In Aviation?
Radio telephony provides the means by which pilots and ground personnel communicate with each other. Used properly, the information and instructions transmitted are of vital importance in assisting in the safe and expeditious operation of aircraft. However, the use of non-standard procedures and phraseology can cause misunderstanding. Incidents and accidents have occurred in which a contributing factor has been the misunderstanding caused by the use of non-standard phraseology. The importance of using correct and precise standard phraseology cannot be over-emphasised.
The following transmitting techniques will assist in ensuring that transmitted speech is clearly and satisfactorily received.
a) Before transmitting check that the receiver volume is set at the optimum level and listen out on the frequency to be used to ensure that there will be no interference with a transmission from another station.
b) Be familiar with microphone operating techniques and do not turn your head away from it whilst talking or vary the distance between it and your mouth. Severe distortion of speech may arise from:
i) Talking too close to the microphone
ii) Touching the microphone with the lips
iii) Holding the microphone or boom (of a combined headset/microphone system).
c) Use a normal conversation tone, speak clearly and distinctly.
d) 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 recipients, speak at a slightly slower rate.
e) Maintain the speaking volume at a constant level.
f) A slight pause before and after numbers will assist in making them easier to understand.
g) Avoid using hesitation sounds such as ‘er’.
h) Depress the transmit switch fully before speaking and do not release it until the message is complete. This will ensure that the entire message is transmitted. However, do not depress transmit switch until ready to speak.
i) Be aware that the mother tongue of the person receiving the message may not be English. Therefore, speak clearly and use standard radiotelephony (RTF) words and phrases wherever possible.
One of the most irritating and potentially dangerous situations in radiotelephony is a ‘stuck’ microphone button. Operators should always ensure that the button is released after a transmission and the microphone placed in an appropriate place that will ensure that it will not inadvertently be switched on.
After a call has been made, a period of at least 10 seconds should elapse before a second call is made. This should eliminate unnecessary transmissions while the receiving station is getting ready to reply to the initial call.
Transmission of Letters
- The words in the table below shall be used when individual letters are required to be transmitted. The syllables to be emphasised are underlined.
|I||India||IN DEE AH|
|J||Juliett||JEW LEE ETT|
|N||November||NO VEM BER|
|R||Romeo||ROW ME OH|
|S||Sierra||SEE AIR RAH|
|U||Uniform||YOU NEE FORM|
Transmission of Numbers
- The syllables to be emphasised are underlined.
|Numeral or numeral element||Latin alphabet representation|
All numbers, except those contained in paragraph above shall be transmitted by pronouncing each digit separately as follows:
- When transmitting messages containing aircraft callsigns, altimeter settings, flight levels (with the exception of FL 100, 200, 300 etc. which are expressed as ‘Flight Level (number) HUN DRED’), headings, wind speeds/directions, pressure settings, transponder codes and frequencies, each digit shall be transmitted separately; examples of this convention are as follows:
|Number||Transmitted as||Pronounced as|
|BAW246||Speedbird Two Four Six||SPEEDBIRD TOO FOWER SIX|
|FL 100||Flight Level One Hundred||FLIGHT LEVEL WUN HUN DRED|
|FL 180||Flight Level One Eight Zero||FLIGHT LEVEL WUN AIT ZERO|
|150 Degrees||One Five Zero Degrees||WUN FIFE ZERO DEGREES|
|18 Knots||One Eight Knots||WUN AIT KNOTS|
|122.1||One Two Two Decimal One||WUN TOO TOO DAYSEEMAL WUN|
|6500||Six Five Zero Zero||SIX FIFE ZERO ZERO (SQUAWK)|
- All numbers used in the transmission of altitude, height, cloud height, visibility and runway visual range information which contain whole hundreds and whole thousands shall be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or TOUSAND as appropriate. Combinations of thousands and whole hundreds shall be transmitted by pronouncing each digit in the number of thousands followed by the word THOUSAND and the number of hundreds followed by the word HUNDRED; examples of this convention are as follows:
|Number||Transmitted as||Pronounced as|
|10||One Zero||WUN ZERO|
|100||One Hundred||WUN HUN DRED|
|2 500||Two Thousand Five Hundred||TOO TOUSAND FIFE HUNDRED|
|11 000||One One Thousand||WUN WUN TOUSAND|
|25 000||Two Five Thousand||TOO FIFE TOUSAND|
- Numbers containing a decimal point shall be transmitted as prescribed in above with the decimal point in appropriate sequence being indicated by the word decimal.
- All six figures shall be used when identifying frequencies irrespective of whether they are 25 kHz or 8.33 kHz spaced. Exceptionally, when the final two digits of the frequency are both zero, only the first four digits need be given.
|Frequency||Transmitted as||Pronounced as|
|118.125||One One Eight Decimal One Two Five||WUN WUN AIT DAY SEE MAL WUN TOO FIFE|
|119.050||One One Nine Decimal Zero Five Zero||WUN WUN NINER DAY SEE MAL ZERO FIFE ZERO|
|122.500||One Two Two Decimal Five||WUN TOO TOO DAY SEE MAL FIFE|
|118.000||One One Eight Decimal Zero||WUN WUN AIT DAY SEE MAL ZERO|
When it is necessary to verify the accurate reception of numbers the person transmitting the message shall request the person receiving the message to read back the numbers.
Transmission of Time
When transmitting time, only the minutes of the hour are normally required. However, the hour should be included if there is any possibility of confusion. Time checks shall be given to the nearest minute. Co-ordinated Universal Time (UTC) is to be used at all times, unless specified. 2400 hours designates midnight, the end of the day, and 0000 hours the beginning of the day
|Number||Transmitted as||Pronounced as|
|0823||Two Three or Zero Eight Two Three||TOO TREE (or ZERO AIT TOO TREE)|
|1300||One Three Zero Zero||WUN TREE ZERO ZERO|
|2057||Five Seven or Two Zero Five Seven||FIFE SEVEN (or TOO ZERO FIFE SEVEN)|
Standard Words and Phrases
The following words and phrases shall be used in radiotelephony communications as appropriate and shall have the meaning given below:
|ACKNOWLEDGE||Let me know that you have received and understood this message.|
|APPROVED**||Permission for proposed action granted.|
|BREAK||Indicates the separation between messages.|
|BREAK BREAK||Indicates the separation between messages transmitted to different aircraft in a busy environment.|
|CANCEL||Annul the previously transmitted clearance.|
|CHANGING TO||I intend to call . . . (unit) on . . . (frequency).|
|CHECK||Examine a system or procedure. (Not to be used in any other context. No answer is normally expected.)|
|CLEARED ‡||Authorised to proceed under the conditions specified.|
|CLIMB ‡||Climb and maintain.|
|CONFIRM||I request verification of: (clearance, instruction, action, information).|
|CONTACT||Establish communications with … (your details have been passed).|
|CORRECT||True or accurate.|
|CORRECTION||An error has been made in this transmission (or message indicated). The correct version is …|
|DESCEND ‡||Descend and maintain.|
|FANSTOP||I am initiating a practice engine failure after take off. (Used only by pilots of single engine aircraft.) The response should be,
“REPORT CLIMBING AWAY”.
|FREECALL||Call . . . (unit) (your details have not been passed – mainly used by military ATC).|
|HOLD SHORT**||Stop before reaching the specified location .|
|Note: Only used in limited circumstances where no defined|
|point exists (e.g. where there is no suitably located holding|
|point), or to reinforce a clearance limit.|
|HOW DO YOU READ||What is the readability of my transmission?|
|I SAY AGAIN||I repeat for clarity or emphasis.|
|MAINTAIN ‡||Continue in accordance with the condition(s) specified or in its|
|literal sense, e.g. “Maintain VFR”.|
|MONITOR||Listen out on (frequency).|
|NEGATIVE||No; or Permission not granted; or That is not correct; or Not|
|OUT*||This exchange of transmissions is ended and no response is|
|OVER*||My transmission is ended and I expect a response from you.|
|PASS YOUR MESSAGE||Proceed with your message.|
|READ BACK||Repeat all, or the specified part, of this message back to me|
|exactly as received.|
|REPORT **||Pass requested information.|
|REQUEST||I should like to know … or I wish to obtain …|
|ROGER||I have received all your last transmission.|
|Note: Under no circumstances to be used in reply to a question|
|requiring a direct answer in the affirmative (AFFIRM) or|
|SAY AGAIN||Repeat all, or the following part of your last transmission.|
|SPEAK SLOWER||Reduce your rate of speech.|
|STANDBY||Wait and I will call you.|
|Note: No onward clearance to be assumed. The caller would|
|normally re-establish contact if the delay is lengthy. STANDBY|
|is not an approval or denial.|
|UNABLE||I cannot comply with your request, instruction or clearance.|
|Unable is normally followed by a reason.|
|WILCO||I understand your message and will comply with it|
|(abbreviation for will comply)|
|WORDS TWICE||As a request: Communication is difficult. Please send every|
|As Information: Since communication is difficult, every word in|
|this message will be sent twice.|
Callsigns for Aeronautical Stations
- Aeronautical stations are identified by the name of the location followed by a suffix except that the name of the rig/platform/vessel is normally used by offshore mineral extraction agencies. The suffix indicates the type of service being provided.
|Radar (in general)||RADAR|
|Approach Control Radar||DIRECTOR/DEPARTURE (RADAR – when tasks combined)/|
|Arrival/Departure||ARRIVAL – (when approved))|
|Ground Movement Control||GROUND|
|Precision Approach Radar||TALKDOWN (Military – FINAL CONTROLLER)|
There are three main categories of aeronautical communications service:
- Air Traffic Control Service (ATC) which can only be provided by licensed Air Traffic Control Officers who are closely regulated by the CAA.
- Flight Information Service at aerodromes can be provided only by licensed Flight Information Service Officers (FISOs), who are also regulated by the CAA.
- Aerodrome Air/Ground Communication Service (AGCS) which can be provided by Radio Operators who are not licensed but have obtained a certificate of competency to operate radio equipment on aviation frequencies from the CAA. These operations come under the jurisdiction of the radio license holder, but are not regulated in any other way.
It is an offence to use a callsign for a purpose other than that for which it has been notified.
When satisfactory communication has been established, and provided that it will not be confusing, the name of the location or the callsign suffix may be omitted.
It is correct procedure to announce identity on all telephone calls: with incoming calls it is the opening remark and with outgoing calls it is the reply to the recipient’s announcement of identity. FISOs and AGCS operators must never identify themselves as ‘….air traffic control’. It is just as important that this procedure is not relaxed for direct telephone lines because mistaken identity can occur when another line has been inadvertently left open from a previous call. The identity to be used is that of the function relative to the telephone extension being used.
Callsigns for Aircraft
- When establishing communication, an aircraft shall use the full callsigns of both stations.
|Delhi Tower G-ABCD||G-ABCD Delhi Tower|
- After satisfactory communication has been established and provided that no confusion is likely to occur, the ground station may abbreviate callsigns (see table below). A pilot may only abbreviate the callsign of his aircraft if it has first been abbreviated by the aeronautical station.
|Speedbird GBGDC||Speedbird DC|
|AI 640||No abbreviation|
|* Piper GBSZT||Piper ZT|
* The name of either the aircraft manufacturer, or name of aircraft model, or name of the aircraft category (e.g. helicopter or gyrocopter) may be used as a prefix to the callsign.
- An aircraft should request the service required on initial contact when freecalling a ground station. .
Delhi Approach, G-ABCD request Radar Information Service
Delhi Control, G-ABCD I wish to file an airborne flight plan
- An aircraft shall not change its callsign type during a flight. However, where there is a likelihood that confusion may occur because of similar callsigns, an aircraft may be instructed by an air traffic service unit (ATSU) to change the type of its callsign temporarily.
- Aircraft in the heavy vortex wake category shall include the word ‘HEAVY’ immediately after the aircraft callsign in the initial call to each ATSU.
Continuation of Communications
- The placement of the callsigns of both the aircraft and the ground station within an established RTF exchange should be as follows:
Ground to Air: Aircraft callsign – message or reply.
Air to Ground:
- Initiation of new information/request etc. – Aircraft callsign then message;
- Reply – Repeat of pertinent information/readback/acknowledgement then aircraft callsign.
|G-ABCD descend FL 80||Descend FL 80 G-ABCD|
G-ABCD maintaining FL 80
|G-ABCD request descent||G-CD descend FL 40|
|Descend FL 40 G-CD|
- When it is considered that reception is likely to be difficult, important elements of the message should be spoken twice.
- When a ground station wishes to broadcast information to all aircraft likely to receive it, the message should be prefaced by the call ‘All stations’.
No reply is expected to such general calls unless individual stations are subsequently called upon to acknowledge receipt.
- If there is doubt that a message has been correctly received, a repetition of the message shall be requested either in full or in part.
|Say again||Repeat entire message|
|Say again … (item)||Repeat specific item|
Say again all before … (the first word satisfactorily received)
Say again all after … (the last word satisfactorily received)
Say again … (word before missing portion) to … (word after missing portion)
When a station is called but is uncertain of the identification of the calling station, the calling station should be requested to repeat its callsign until identification is established.
|Delhi Ground Fastair 345||Station calling Delhi Ground say again your callsign|
Corrections and Repetitions
- When an error is made in a transmission the word ‘CORRECTION’ shall be spoken, the last correct group or phrase repeated and then the correct version transmitted.
Fastair 345 Akela 47 FL 280 Bavox 07 correction Bavox 57
Fastair 345 Roger
- If a correction can best be made by repeating the entire message, the operator shall use the phrase ‘CORRECTION I SAY AGAIN’ before transmitting the message a second time.
Acknowledgement of Receipt
Acknowledgements of information should be signified by the use of the receiving stations’ callsign or Roger callsign, and not by messages such as: ‘callsign-copy the weather’ or ‘callsign-copy the traffic’.
Transfer of Communications
- An aircraft will normally be advised by the appropriate aeronautical station to change from one radio frequency to another in accordance with agreed procedures.
|Fastair 345 contact Delhi Control 129.125||Delhi Control 129.125 Fastair 345|
In the absence of such advice, the aircraft shall notify the aeronautical station before such a change takes place. Aircraft flying in controlled airspace must obtain permission from the controlling authority before changing frequency.
- An aircraft may be instructed to ‘standby’ on a frequency when it is intended that the ATSU will initiate communications, and to monitor a frequency on which information is being broadcast.
Fastair 345 standby 118.950 for Delhi Tower
Standby 118.950 for Delhi Tower Fastair 345
|Fastair 345 monitor 128.275 for ATIS||Monitor 128.275 for ATIS Fastair 345|
- If the airspace does not dictate that an aircraft must remain in contact with a specific ATSU and the pilot wishes to freecall another agency he should request, or notify such an intention.
Delhi Approach G-ABCD request change to Delhi Information on 125.750
Clearance Issue and Read Back Requirements
- Provisions governing clearances are contained in the PANS-ATM (ICAO Doc 4444). A clearance may vary in content from a detailed description of the route and levels to be flown to a brief standard instrument departure (SID) according to local procedures.
- Controllers will pass a clearance slowly and clearly since the pilot needs to write it down; wasteful repetition will thus be avoided. Whenever possible, a route clearance should be passed to an aircraft before start up and the aircraft’s full callsign will always be used. Generally, controllers will avoid passing a clearance to a pilot engaged in complicated taxiing manoeuvres and on no occasion when the pilot is engaged in line up or take-off manoeuvres.
- An ATC route clearance is NOT an instruction to take-off or enter an active runway.
The words ‘TAKE-OFF’ are used only when an aircraft is cleared for take-off. At all other times the word ‘DEPARTURE’ is used.
The stringency of the read back requirement is directly related to the possible seriousness of a misunderstanding in the transmission and receipt of ATC clearance and instructions. ATC route clearances shall always be read back unless otherwise authorised by the appropriate ATS authority in which case they shall be acknowledged in a positive manner. Read backs shall always include the aircraft callsign.
- Fastair 345 cleared to Mumbai via A474, at FL 160, request level change en-route, squawk 5501
- Cleared to Mumbai via A474, request level change enroute, squawk 5501 Fastair 345
- Fastair 345 correct
The ATS messages listed below are to be read back in full by the pilot/driver. If a readback is not received the pilot/driver will be asked to do so. Similarly, the pilot/ driver is expected to request that instructions are repeated or clarified if any are not fully understood.
- Taxi/Towing Instructions
- Level Instructions
- Heading Instructions
- Speed Instructions
- Airways or Route Clearances Approach Clearances Runway-in-Use
- Clearance to Enter, Land On, Take-Off On, Backtrack, Cross, or Hold Short of any Active Runway
- SSR Operating Instructions
- Altimeter Settings
- VDF Information
- Frequency Changes
- Type of Radar Service
- Transition Levels
G-ABCD cleared to cross A474 at P’Garh, maintain FL 70 whilst in controlled airspace. Report entering the airway
Cleared to cross A474 at P’ Garh, maintain FL 70 in controlled airspace, Wilco. G-ABCD
- If an aircraft read back of a clearance or instruction is incorrect, the controller shall transmit the word ‘NEGATIVE’ followed by the correct version.
|G-CD QNH 1003||QNH 1013 G-CD|
|G-CD Negative, QNH 1003|
|QNH 1003, G-CD|
If at any time a pilot receives a clearance or instruction with which he cannot comply, he should advise the controller using the phrase ‘UNABLE’ (COMPLY) and give the reason(s).
- Fastair 345 Delhi climb FL 280, cross Alpha FL 150 or above
- Delhi Fastair 345 unable cross Alpha FL 150 due weight
Complying with Clearances and Instructions
Pilots are expected to comply with clearances and instructions promptly, commensurate with normal aircraft operations. If, for any reason, a pilot does not wish to comply with an instruction promptly, the pilot should advise the ATS unit and give an indication of when he intends to comply.
- If an ATS unit wishes to indicate that time of compliance is at pilot’s discretion, the ATS message will include the phrase ‘when ready’.
- If an ATS unit wishes to indicate that the clearance or instruction is required to be complied with at a particular point in the flight, the message will include the phrase ‘after passing’.
- If an ATS unit wishes to indicate that the instruction or clearance must be complied with at once, the controller’s message will include the word ‘now’ or ‘immediately’. Use of the word ‘now’ indicates that the instruction should be complied with in accordance with normal aircraft operating procedures, but without undue delay. Use of the word ‘immediately’ indicates a further degree of urgency exists. In such circumstances, the pilot should take action to comply with the instruction as soon as practicable, subject to the safety of the aircraft.
- In order to ensure any restriction is not blocked by a pilot acknowledgement, the phrase or word, indicating when a clearance or instruction should be complied with, will normally be placed before the executive instruction, but in certain cases the phrase or word may be placed between the instruction and the value of the instruction.
Air – Ground
Check the following points:
- The correct frequency has been selected for the route being flown.
- The Aeronautical Station being called is open for watch.
- The aircraft is not out of radio range.
- Receiver volume correctly set.
- If the previous points are in order it may be that the aircraft equipment is not functioning correctly. Complete the checks of headset and radio installation appropriate to the aircraft.
- When an aircraft station is unable to establish contact with the aeronautical station on the designated frequency it shall attempt to establish contact on another frequency appropriate to the route being flown. If this attempt fails, the aircraft station shall attempt to establish communication with other aircraft or other aeronautical stations on frequencies appropriate to the route.
- The pilot may still be unable to establish communication on any designated aeronautical station frequency, or with any other aircraft. The pilot is then to transmit his message twice on the designated frequency, including the addressee for whom the message is intended, preceded by the phrase ‘TRANSMITTING BLIND’ in case the transmitter is still functioning.
- Where a transmitter failure is suspected, check or change the microphone. Listen out on the designated frequency for instructions. It should be possible to answer questions by use of the carrier wave if the microphone is not functioning (see Chapter 8 paragraph 1.6).
- In the case of a receiver failure transmit reports twice at the scheduled times or positions on the designated frequency preceded by the phrase ‘TRANSMITTING BLIND DUE TO RECEIVER FAILURE’.
- An aircraft which is being provided with air traffic control service, advisory service or aerodrome flight information service is to transmit information regarding the intention of the pilot in command with respect to the continuation of the flight. Specific procedures for the action to be taken by pilots of IFR and Special VFR flights are contained in the appropriate AIP ENR and/or AD sections.
Ground – Air
- After completing checks of ground equipment (most airports have standby and emergency communications equipment) the ground station will request other aeronautical stations and aircraft to attempt to communicate with the aircraft which has failed to maintain contact.
- If still unable to establish communication the aeronautical station will transmit messages addressed to the aircraft by blind transmission on the frequency on which the aircraft is believed to be listening.
- These will consist of:
- The level, route and EAT (or ETA) to which it is assumed the aircraft is adhering.
- The weather conditions at the destination aerodrome and suitable alternate and, if practicable, the weather conditions in an area or areas suitable for descent through cloud procedure to be effected. (See AIP ENR Section.)
- Test Transmissions
- All radio transmissions for test purposes shall be of the minimum duration necessary for the test and shall not continue for more than 10 seconds. The recurrence of such transmissions shall be kept to the minimum necessary for the test.
- The nature of the test shall be such that it is identifiable as a test transmission and cannot be confused with other communications. To achieve this the following format shall be used:
- the callsign of the aeronautical station being called;
- ‘the aircraft identification’;
- the words ‘RADIO CHECK’;
- ‘the frequency’ being used;
- The operator of the aeronautical radio station being called will assess the transmission and will advise the aircraft making the test transmission in terms of the readability scale (Table 11), together with a comment on the nature of any abnormality noted (i.e. excessive noise) using the following format:
- ‘the aircraft identification’;
- ‘the callsign’ of the aeronautical station replying;
- ‘READABILITY x’ (where ‘x’ is a number taken from Table 11);
- ‘additional information’ with respect to any noted abnormality;
NOTE: For practical reasons it may be necessary for the operator of an aeronautical station to reply with ‘STATION CALLING (frequency or 8.33 channel) UNREADABLE’.
Video Courtesy YOUTUBE