What is meant by “Five by Five”?
Have you ever wondered what is meant by the term “Five by Five?” You’ll hear this sometimes as a response when an aircraft or tower is asking for a radio check:
“Citation XYY, how do you hear this transmitter?”
“5 by 5″
Well, I’ve heard this term used countless times and it was a recent transmission that finally motivated me to do some research. I wanted to find out exactly what is meant by that term “5 by 5″ when I heard an aircraft respond to a radio check by saying:
“I hear you 3 by 5.”
Ok, so what transmission quality is represented by the “3″ and what is represented by the “5″.
Well, thanks to my local tower controllers, I learned that the first number is for signal strength and the second number is for readability. Signal strength and readability are measured on a five point scale with 5 being the highest value possible and 1 being the lowest. So when you say to the controller (or pilot) “5 by 5″, it is literally another way of saying that the transmitter you hear is “loud and clear.” If you say “3 by 5″ it’s like saying, “Your coming in kind of weak, but I can still make out what your saying”
So now you too know the meaning of the term “Five by Five”.
Sarah on Apr 10, 2009
Interesting. I’d always heard it the other way around, the first number being readability and the 2nd strength. From olden days radio, the system was called the “RST”, “readability/strength/tone” 5x5x9 scale. The “tone” refers to dah-dit-dah-dah tone.
Here: http://en.wikipedia.org/wiki/RST_code
Moot.. anyway. 99.9% of the time the response is “5×5″.
Danny V on Apr 10, 2009
In Canada, this is how we are taught to do radio checks. “# by #” is the response format we expect when we ask for a radio check.
The scales are as follow (in the format # – readability scale – strength):
1 – unreadable – bad
2 – now & then – poor
3 – with difficulty – fair
4 – readable – good
5 – perfect – excellent
So a “3 by 5″ means (as you said) “with difficulty but signal strength is excellent.”
Keep up the great job!
Paul on Apr 10, 2009
So readability and strength seems to be the answer, not strength and quality. Thanks for the correction.
Jeremy on Apr 10, 2009
There seems to be a lot of confusion on which number is which. Remember that on AM radio, which includes aircraft bands, signal strength and volume (loudness) are equivalent. So you didn’t fully correct your blog post, because if the reading were “3 x 5″ and the first number is readability, that would mean a maginally readable signal but perfectly loud/strong. For example it might be full of crackles and pops, or a bad microphone, or background noise, or something like that – but still fully loud and strong. A weakish signal that is otherwise readable would be ’5 x 3′ after your correction.
There is a lot of disagreement as to which number is which – I’ve seen dozens of references to both. After all, the catchphrase “loud and clear” would mean that strength comes first and readability second, right? I actually think this is the more common method, not the method Sarah suggests, but it’s certainly ambiguous.
To resolve this ambiguity problem, in Australia the required response to a radio check question is something like, “strength 5, readability 4″.
By the way, the strength is supposed to be on a scale of 1-10. A strength of 5 is normal – if it were something higher it would mean you were overpowering the transmitter and overloading receiving speakers or something. Most people forget this though as modern radios are pretty good about not doing that, and the only issue is weaker than normal signals. Readability is indeed a 1-5 scale.
Hope this helps,
Jeremy
Paul on Apr 11, 2009
Jeremy,
Your right on several accounts. The RST scales have strength on a 1-10 scale, not 1-5.
I’m going to do a little more digging.
On a rather funny note, I have something to admit. When I asked my local controller for his source for his answer, you know what he said? WIKIPEDIA!!!
So apparently, I need to do a better job of checking my sources!
Paul on Apr 11, 2009
Ok. I have reverted to my original post content (Goolge is going to LOVE me). The reason for this is that I think it can be interpreted either say. I think Jeremy has the right answer that when asked for a radio check, the appropriate response should be (on a 1-5 scale) “signal strenth 5, readability 3″ or you can reverse it, as long as you give the term before the value. So, that’s my answer until I see a written authoritative source that applies to aviation (FAA or ICAO) and then I’ll of course change it…
Paul on Apr 12, 2009
Paul,
your blog currently states “first number is for signal strength and the second number is for signal strength”, which I’m assuming is a mistake after you changed it.
As a military signaller and later military pilot, I was always taught 5 by 5 as in loud and clear, meaning strength and readability is the correct way around. Hope that helps.
Paul on Apr 12, 2009
Paul. Yes, thanks for that catch. It has been updated now to the original content which is in agreement with your meaning of 5 by 5 which is strength then readability.
Geesh..I’m struggling a little with this post.
John Elliot on Jun 18, 2009
all this comes from old time phraseology, 5 by 5 is still LOUD & CLEAR, same answer to QSA QRK as the question.
In Peru we still use terms such as QDM QDR QAB QTA Etc as normal ATC lingo.
From an old timer.
John