ICAO Radiotelephony Transmission Standards and Phraseology

090-02-01Pablo Asensio Martínez2026-04-014 min

Standard Phraseology

Standard phraseology is essential to ensure clear and unambiguous communication. The following table lists common phrases and their meanings according to ICAO Annex 10, Volume II and Doc 9432.

Phrase Meaning
ACKNOWLEDGE Let me know that you have received and understood this message.
AFFIRM Yes.
APPROVED Permission for proposed action granted.
BREAK Indicates separation between portions of a message.
BREAK BREAK Indicates separation between messages to different aircraft.
CANCEL Annul the previously transmitted clearance.
CONFIRM I request verification of: (clearance, instruction, action, information).
CONTACT Establish communications with...
CORRECT True or Accurate.
CORRECTION An error has been made in this transmission. The correct version is...
DISREGARD Ignore.
GO AHEAD Proceed with your message.
HOW DO YOU READ What is the readability of my transmission?
I SAY AGAIN I repeat for clarity or emphasis.
MONITOR Listen out on (frequency).
NEGATIVE No, or Permission not granted, or That is not correct.
READ BACK Repeat all, or the specified part, of this message back to me exactly as received.
RECLEARED A change has been made to your last clearance and this new clearance supersedes your previous clearance.
REPORT Pass me the following information...
ROGER I have received all of your last transmission. (Do not use for readbacks).
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.
UNABLE I cannot comply with your request, instruction, or clearance.
WILCO I understand your message and will comply with it.

Readback Requirements

To ensure safety, specific parts of ATC clearances and instructions must always be read back in full (ICAO Doc 4444):

  1. ATC route clearances.
  2. Clearances and instructions to enter, land on, take off from, hold short of, cross, taxi and backtrack on any runway.
  3. Runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and transition levels.

Note: Determining "Identification Lost" does not require a readback, "Roger" is sufficient.

Aircraft Call Signs

Call signs are used to identify aircraft and prevent confusion.

Types of Call Signs

  • Type A: Registration only (e.g., G-ABCD).
  • Type B: Telephony designated of agency + Last 4 characters of registration (e.g., FASTAIR DCAB).
  • Type C: Telephony designated of agency + Flight ident (e.g., FASTAIR 345).

Abbreviation Rules

  • Type A: First character + Last two (e.g., G-CD).
  • Type B: Designator + Last two (e.g., FASTAIR AB).
  • Type C: No abbreviated form allowed.
  • Important: A pilot can abbreviate their call sign ONLY after the controller has addressed them using the abbreviated call sign first.

Call Sign Confusion

If call signs are similar (e.g., Airline 123 and Airline 132), ATC may instruct an aircraft to change its call sign temporarily.

  • Instruction: "CHANGE YOUR CALL SIGN TO..."
  • Reverting: "REVERT TO FLIGHT PLAN CALL SIGN..." (The pilot cannot revert automatically).

Wake Turbulence

  • HEAVY: Must be included after the call sign in initial contact for aircraft $\ge$ 136,000 kg.
  • SUPER: Used for aircraft like the A380.

Transmission of Numbers and Time

  • Numbers: Pronounced separately (e.g., 118.1 as "ONE ONE EIGHT DECIMAL ONE").
  • Flight Levels: Hundreds are used for whole hundreds (e.g., FL200 as "TWO HUNDRED").
  • Time: Only minutes are transmitted unless there is confusion (e.g., 09:20 as "TWO ZERO").

Traffic Information

Traffic information is given relative to the aircraft's track:

  • Clock Code: Relative bearing (e.g., "12 o'clock" is directly ahead).
  • Distance: In miles.
  • Direction: Relative movement (e.g., "Opposite direction", "Crossing left to right").

Communications Failure

If radio contact fails (ICAO Annex 10):

  1. Attempt to contact on previous frequency.
  2. Attempt another appropriate frequency.
  3. Check connections/headset.
  4. If unsuccessful, transmit message twice preceded by "TRANSMITTING BLIND".
  5. Set Transponder to 7600.

ATC may ask other aircraft to relay messages if they cannot reach an aircraft directly.

Specific Procedures

Radar Vectoring

  • Vectors: Headings assigned by ATC (e.g., "Turn left heading 215").
  • Termination: ATC will state "RESUME OWN NAVIGATION".

ACAS/TCAS

  • Pilot response to RA: "TCAS RA".
  • Returning to clearance: "CLEAR OF CONFLICT, RETURNING TO..."
  • Resumed clearance: "CLEAR OF CONFLICT, RESUMED..."

SELCAL (Selective Calling)

  • Used in remote areas (HF) to avoid continuous monitoring of noisy frequencies.
  • Phrase to test: "REQUEST SELCAL CHECK".
  • Code example: "ALBM".

RNAV Status

  • If not equipped (State aircraft): "NEGATIVE RNAV".
  • If equipment failure: "UNABLE RNAV DUE EQUIPMENT".