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Repetition is a key characteristic of communication in the control tower, cockpit, and control room. Some phrases, like "Mayday" get repeated. The speaker says the same thing three times. We know this is for redundancy.

Why exactly three times?

Why not twice or four times? Is there research suggesting three is the most effective number, or is there a historical reason for the convention?

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    $\begingroup$ It sounds like you're asking why three, rather than two or four. In other words, you're not just asking "why do we say it three times"; you're asking "why is three the number of times that we say it". Is that right? $\endgroup$ – Tanner Swett Jan 13 at 1:53
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    $\begingroup$ That literally means the exact same thing. $\endgroup$ – Ryan Mortensen Jan 13 at 5:42
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    $\begingroup$ @RyanMortensen No, there's a difference in emphasis. The questions "Why do we say it three times?" and "Why do we say it exactly three times, rather than two or four?" are different questions that invite different answers. If you said "It's for redundancy", that would answer the first question, but not the second. $\endgroup$ – Tanner Swett Jan 13 at 13:05
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    $\begingroup$ Five is right out. $\endgroup$ – Henning Makholm Jan 13 at 21:33
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    $\begingroup$ @HenningMakholm - I joined this community just so I could up-vote your comment :) $\endgroup$ – Tony Jan 14 at 2:41
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Procedure calls for the mayday distress signal to be said three times in a row so that it won't be mistaken for another word or phrase that sounds similar under noisy conditions. The use of Mayday dates back to 1923 when it was first used because it sounded like the French word m'aider, which means “Help me." In those early days of radio it was necessary to repeat things sometimes because of interference on the frequency from various potential sources.

The "rule of three" is rooted in research conducted in 1890 by Hermann Ebbinghaus, a German psychologist. Ebbinghuas studied how many rehearsals were necessary for his test subjects to memorize a list of nonsense syllables. He came up with three as the optimal number, and that became a rule of thumb in many other things, such as advertising.

Here's a cool video that adds information on Mayday and Pan Pan.

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    $\begingroup$ Just a small correction, it is "m'aidez" $\endgroup$ – infinitezero Jan 14 at 22:07
  • $\begingroup$ @infinitezero Oui ! "M'aidez!" is an imperative meaning "(You) help me!" However, "m'aider" means "to help me", e.g. in a full sentence "I would like someone to help me" (Je voudrais que quelqu'un m'aider). $\endgroup$ – CJ Dennis Jan 15 at 2:08
  • $\begingroup$ @CJDennis Note that "Je voudrais que quelqu'un m'aider" is incorrect, it would more likely by "Je voudrais que quelqu'un m'aide". On the other hand, "I would like someone to come help me" would be "Je voudrais que quelqu'un vienne m'aider". (Also "M'aidez!" feels very strange to me. "Help me!" would be "Aidez-moi !") $\endgroup$ – Rafalon Jan 15 at 9:56
  • $\begingroup$ @Rafalon I don't think I (or anyone else I know) would say those things. As you say Aidez / aide moi would suffice rather than such a long sentence :) $\endgroup$ – Cloud Jan 15 at 11:26
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    $\begingroup$ @Cloud Sure thing. I should have made clear that my point is: "m'aidez" is incorrect unless maybe in very old French (I'm French and I've never seen a sentence including it), and "m'aider" must follow a verb ("Venez m'aider") $\endgroup$ – Rafalon Jan 15 at 12:11
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Yep, the critical commands are repeated 3 times. This ensures there is ABSOLUTELY zero doubt in anyone's mind (especially on a big crew airplane) of what needs to be done in a critical situation. It also standardizes these criticalities across different aircraft and aircrew cultures. "Bail out, bail out, bail out" "Eject, eject, eject" "Abort abort abort" "Pan-pan, pan-pan, pan-pan." I was 27 years a USAF pilot, and this is how the training has worked for over 50 years. I only saw these terms used 2-3 times, but it certainly gets your attention and amps up the sense of urgency. A little history: back in the day of very poor radio communications, it was necessary to repeat to "get someone's attention" or in the event a single "mayday" didn't come across when the transmit button was pressed.

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    $\begingroup$ Need clarification. Does emergency "pan" only mentioned 3 times? I heard a senior commercial pilot said that it must be mentioned six times as it only 1 syllable: "Pan-pan, pan-pan, pan-pan". $\endgroup$ – AirCraft Lover Jan 13 at 5:20
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    $\begingroup$ @AirCraftLover I believe this is is correct. I read a pronunciation manual that described it as "Pahn-pahn", so that would be one iteration, not two, so you're right. 3 pairs of two "pan"s. $\endgroup$ – Ryan Mortensen Jan 13 at 5:44
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    $\begingroup$ @AirCraft Lover If you take a look at historical editions of ITU's Radio Regulations, and compare it with current, you'll be able to see that there's been a change. The urgency signal was changed from "pan" to "pan-pan". Therefore, it is repeated 3 times, and not 6, but the signal itself has word pan two times in it now. $\endgroup$ – AndrejaKo Jan 13 at 7:06
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    $\begingroup$ The question does ask about research and historical convention on the number of repetitions. No answer has addressed this part of the question. Whether there is research, there is definitely historical convention about saying things three times for emphasis, that goes back thousands of years. $\endgroup$ – JdeBP Jan 13 at 13:55
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    $\begingroup$ I agree with @JdeBP -- since the dawn of radio telephony (or telegraph), is there historical evidence for why it is repeated exactly three times. $\endgroup$ – Mark Jones Jr. Jan 14 at 2:56
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There are no instances in normal conversation where the same word is repeated three times consecutively. In order to prevent a critical command or order from being issued or heard accidentally, a command is given three times in order to verify that it is being given intentionally.

Going to the moon? “Launch! Launch! Launch!”

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    $\begingroup$ This doesn't seem at all sensible, since any given phrase could be only heard once by the receiver if e.g. the first copy was snapped by a button delay and the second lost in static. The answer by Scotty provides the much more sensible historic basis: three times for redundancy. $\endgroup$ – Nij Jan 13 at 8:25
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    $\begingroup$ This doesn't answer why they say it ** 3 (three)** times and not four, tow, five, or seven times. $\endgroup$ – Alexandre Aubrey Jan 14 at 22:23
  • $\begingroup$ do you have sources for your statements? $\endgroup$ – Federico Jan 15 at 7:25
  • $\begingroup$ "Tora! Tora! Tora!" apparently supports this claim. $\endgroup$ – Agent_L Jan 15 at 15:16
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I assume it's for redundancy. Assuming the voice signal is very noisy, the listener might hear two different things, the first and second time. The third repetition can then be used to decide which of the two versions heard is more likely to be the correct one.

Majority voting with three signals is very common in redundant systems. In computing it is called TMR (triple modular redundancy). https://en.wikipedia.org/wiki/Triple_modular_redundancy

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  • $\begingroup$ "I assume". you got any source? $\endgroup$ – Federico Jan 15 at 7:24
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Because human brains are slow and easily distracted?

The first time you heard it - you started listening.

The second time you heard it - you started listening properly, because you know it's important

The third time confirmed you heard what you thought you heard?


This is just my unresearched perception of what's going on, and why we naturally settled on saying thing 3 times when it's imperative that it's heard properly.

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    $\begingroup$ Wouldn't this imply also that a large number of initial calls to various air traffic controllers would need to be repeated? The fact that that's generally not necessary would seem to suggest that your perception is, if not wrong, then at least not entirely correct. $\endgroup$ – a CVn Jan 14 at 21:32
  • $\begingroup$ I don't know exactly how a call coming into a air traffic controller sounds - i.e. if there's a bleep or something first. I'm thinking about situations where you're concentrating on multiple things already, and something needs to desperately grab your attention. $\endgroup$ – djsmiley2k Jan 14 at 21:38
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    $\begingroup$ I'm pretty sure there is no beep or anything; there would be little value, and any such thing could risk masking the first portion of a transmission. That said, even when flying, with engine and propeller noise in the cockpit, I've never had any trouble telling when a transmission began or ended; it's pretty distinctive. I have had trouble hearing what people said on the radio once or twice when they wouldn't speak up, but in that case, repeating a single word a few times likely won't help much. $\endgroup$ – a CVn Jan 14 at 21:48
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    $\begingroup$ if this is just your unresearched perception it is not an answer. please provide sources for your statements. $\endgroup$ – Federico Jan 15 at 7:25
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the reason for the repetition of mayday mayday mayday is for receiver of the messages can hear the callings, if the first mayday calling is breaking, the second mayday calling maybe be heard, and totally sure the third mayday the messages needs to be convey along with the mayday

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    $\begingroup$ This answer could be greatly improved by beginning each sentence with a capital letter and ending it with a period. I can't tell where the sentences here begin and end. $\endgroup$ – Tanner Swett Jan 14 at 1:00
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    $\begingroup$ This doesn't answer why they say it ** 3 (three)** times and not four, tow, five, or seven times. $\endgroup$ – Alexandre Aubrey Jan 14 at 22:25

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