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Message Format and Content

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Category: Air Ground Communication Air Ground Communication
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The purpose of all RTF messages is to convey information or instructions unambiguously to a specific recipient or recipients. Use of standard format and content will help to achieve this purpose.

Use of non-standard message format and/or content may result in one or more of the following undesirable outcomes:

  • The message is not received by the intended recipient;
  • All or part of the message is misunderstood;
  • Parts of the message may be confused and incorrectly acted on.

Composition of Messages

The following provisions abridged from ICAO Annex 10 Volume II, Chapter 5, Section 5.2.1. are designed to achieve the above objectives:

Messages ... shall comprise the following parts in the order stated:

a) call-sign indicating the addressee and the originator;
b) text.

Note.— The following examples illustrate the application of this procedure:




When the text of a message to be transmitted ... to an aircraft in flight contains approved ICAO abbreviations, these abbreviations should normally be converted during the transmission of the message into the unabbreviated words or phrases which the abbreviations represent in the language used, except for those which, owing to frequent or common practice, are generally understood by aeronautical personnel.

Establishment of radiotelephony communications

Full radiotelephony call-signs shall always be used when establishing communication.

The calling procedure of an aircraft establishing communication shall follow the following format:

Call-sign of station called, followed by call-sign of station calling.

The reply to the above calls shall follow the following format:

Call-sign of the station calling followed by call-sign of the answering station. This shall be considered the invitation to proceed with transmission by the station calling.

Subsequent radiotelephony communications

Abbreviated radiotelephony call signs, shall be used only after satisfactory communication has been established and provided that no confusion is likely to arise. An aircraft station shall use its abbreviated call sign only after it has been addressed in this manner by the aeronautical station.

In order to avoid any possible confusion, when issuing ATC clearances and reading back such clearances, controllers and pilots shall always add the call sign of the aircraft to which the clearance applies.

Communications shall be concise and unambiguous, using standard phraseology whenever available.

The receiving operator shall make certain that the message has been received correctly before acknowledging receipt.

When transmitted by an aircraft station, the acknowledgement of receipt of a message shall comprise the call sign of that aircraft.

An aircraft station should acknowledge receipt of important air traffic control messages or parts thereof by reading them back and terminating the readback by its radio call sign.

Note: Air traffic control clearances, instructions and information requiring readback are specified in PANS-ATM (ICAO Doc 4444).

If the receiving operator is in doubt as to the correctness of the message received, he shall request repetition either in full or in part.

If, in checking the correctness of a readback, an operator notices incorrect items, he shall transmit the words “NEGATIVE I SAY AGAIN” at the conclusion of the readback followed by the correct version of the items concerned.

Non-regulatory advice

The following advice will enhance readability and reduce the chance of misunderstanding:

  • Limit the number of elements in a message to two to reduce the chance of an element being missed or misheard.
  • The elements of an RTF frequency are treated by a pilot as individual digits; therefore, a frequency change should not be combined with another instruction. This also prevents situations where the crew makes incorrect readback of the instruction and leaves the frequency.
  • Avoid combining numerical elements which may easily be confused in the same message, for example, flight level and heading.
  • Preface any non standard instructions with the phrase ‘non standard’ e.g. "descend now non standard level 75", to ensure the pilot notes the differences from standard.
  • Avoid heavy accents or colloquialisms.
  • Give radar headings ending in ‘5’ if confusion with the current range of radar headings might occur.

Related Articles

Further Reading

  • ICAO Annex 10 Volume II Chapter 5;
  • ICAO Doc 4444: PANS-ATM;

EUROCONTROL: The European Action Plan for Air-Ground Communications Safety;