# ICAO Radiotelephony Transmission Standards and Phraseology

> Standard ICAO phraseology, transmission conventions, and key RT terms for clear, unambiguous ATC communication.

- **Subject:** 090 — Communications
- **Section:** 090-02 — General Operating Procedures
- **Topic code:** 090-02-01
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/communications/general-operating-procedures/transmission-standards/

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## 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**".

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