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When a transmission has a readability of 3, what does that mean?

  • A

    The transmission is readable but with difficulty.

  • B

    The transmission is perfectly readable.

  • C

    The transmission is unreadable.

  • D

    The transmission is readable now and then.

Refer to figures.
ICAO Annex 10 Volume II
5.2.1.5 TRANSMITTING TECHNIQUE

5.2.1.8.4 PANS.— When the tests are made, the following readability scale should be used:

Readability Scale

1 Unreadable
2 Readable now and then
3 Readable but with difficulty
4 Readable
5 Perfectly readable


The readability check is done by pilots and air traffic controllers to inquire about the quality and clarity of a radio transmission. During a readability check, they are essentially asking if their message is being heard clearly and if the recipient can understand it well in terms of loudness and lack of any background noise.

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