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I heard a pilot replied "CC" to ATC instruction.

I can't remember the exact situation, but does anyone knows what it means?

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    $\begingroup$ Can you clarify did you hear "CC" or "Charlie Charlie" $\endgroup$
    – RoyC
    Commented Feb 1, 2018 at 22:05

5 Answers 5

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Short answer

Charlie-Charlie is a fancy substitution for a standard affirmative.

It comes from the convention of abbreviating Correct/Yes by letter C in codes. It was early standardized and used at sea since 1857. Under the Commercial Code of Signals (1857-1902), the C flag, in addition of representing the letter itself, had the meaning of Yes/Affirmative.

enter image description here
C flag meaning affirmative

This code has been improved and extended into the International Code of Signals (ICS). While the visual representation changed, the meaning was preserved extended to radiocommunications. From the 2003 ICS:

Signals for flags, radiotelephony, and radiotelegraphy transmissions.
C: Affirmative—YES or “The significance of the previous group should be read in the affirmative”.


Examples

Discovered by @ymb1, this accident investigation report, for a Boeing 747 accident in 1987, includes a transcription of the pilot (CA) controller (MA) exchange:

  • CA: Roger, we will appreciate it if you can alert, er, fire, er, er, er.
  • MA: Do you request a full emergency please? A full emergency?
  • CA: Affirmative, that's Charlie Charlie
  • MA: Roger, I declare a full emergency.

later:

  • MA: Confirm runway one four?
  • CA: Charlie Charlie.

And this other document, still from @ymb1:

  • Do you have ATIS information Delta?
  • Charlie Charlie we have Delta.

...

  • Ok our stand 41 AF028.
  • Understand B 41.
  • Charlie, charlie.
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    $\begingroup$ Formally, "roger," "wilco," and "affirm/affirmative" are not synonyms. "Roger" means "I understand," "wilco" means "I will comply," and "affirmative" means "yes." Usage does differ from the formal meaning, however. $\endgroup$ Commented Feb 1, 2018 at 14:50
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    $\begingroup$ Is this some kind of elaborately layered pun? Charlie -> C -> "C" is pronounced Si (spanish for yes) -> yes $\endgroup$
    – BlackThorn
    Commented Feb 1, 2018 at 18:51
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    $\begingroup$ @BlackThorn: Yes, mnemonic, also No-vember. I'm a little unsure whether "I require medical assistance" being Whisky is a joke or based on reality :-) $\endgroup$
    – mins
    Commented Feb 1, 2018 at 19:15
  • $\begingroup$ @WayneConrad: does "affirmative" mean "I understand", "I will comply" or what? $\endgroup$
    – smci
    Commented Feb 1, 2018 at 21:21
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    $\begingroup$ @smci "Affirmative" is "yes" in response to a yes/no question. "Negative" is "no". $\endgroup$
    – ChrisDevo
    Commented Feb 1, 2018 at 21:38
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CC is short for Click Click. In situations where a military operator was busy or where talking could prove fatal an incoming message would be acknowledged by a double click of the transmit switch on the radio producing a "click click" at the other end.

"CC" somehow got into informal usage rather than the more precise roger wilco or affirmative. In this context it would probably be used as an informal acknowledgement of a purely informational message.

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  • $\begingroup$ Second that, I remember being taught this method of "silent affirmation of receipt" in the US Marines FROC (field radio operators course). $\endgroup$ Commented Feb 1, 2018 at 19:41
  • $\begingroup$ The OP's question was about CC not Charlie Charlie. $\endgroup$
    – RoyC
    Commented Feb 1, 2018 at 22:02
  • $\begingroup$ @mins Added quotes to clarify. $\endgroup$
    – RoyC
    Commented Feb 1, 2018 at 22:17
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To answer the OP's question, "CC" and/or "Charlie Charlie" mean absolutely nothing in air traffic control. In my 30+ years in ATC, I never heard, nor heard of, someone responding to a clearance with that verbiage. If I did, I would repeat the clearance because I had not received a valid read back.

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Flying overseas in the 1970s we used "Charlie Charlie" (not CC) as affirmative mostly on HF (High Frequency) radios. UHF, VHF and FM radios were pretty clear and you could understand a word like affirmative.
But HF was often a weak signal; scratchy and full of static. Charlie Charlie (repeated like that) was better- easier to understand- than one word answers like affirmative. I was a young pilot then and I learned to use it from professional radio operators. I will defer to the other responder regarding it's historical origin.

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    $\begingroup$ Welcome to Aviation.StackExchange! $\endgroup$
    – Ralph J
    Commented May 29, 2023 at 20:59
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"Charlie Charlie" was always "Confirmed Correct" in my understanding. If ATC asked a question like "Is that your final requested level" then "Charlie Charlie" was an acceptable and recognised informal reply.

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