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
Jerry on Aug 24, 2011
So I don’t remember where I read this, but I read that five by five was just a slang term used to mean loud and clear was used by either a British or French pilot years and years ago (spelling loud, “Loude”) thus the term mearly refrenced the words. Since I have never seen a scale describing the clarity vs strength in any official flight publication (FAR/AIM, FIH etc) I like the story I read. Whenever I hear guys on the radio say “3×5” gives me a geek cringe.
Tony on Nov 22, 2013
I’m a ground guy in charge of the comms on a team that controls ord drops. You’ll be happy to know that we simplified it even further by just turning it into, “Five-by”. Meaning, 5×5. We just know that it means comms won’t be the reason we can’t drop today. I was actually talking to another guy on the team about this and we figured it correlated to, “loud and clear”. So I’m here. It’s nice to see the expertise come together from so many places to discover the roots of what otherwise would be just slightly more than daily jargon. The pilots we’ve talked to haven’t really known the whole tale around this term either. Thanks to everyone for the insight.
abe lincoln on Apr 01, 2014
from an old flight engineer, I think this is where it all might have started from.
how is this for an “Authoritative sources”
https://archive.org/details/Fm24-6
check out this old radio operators handbook from WW2. on page 11 it explanse what it means, and when to do and not to do a check, this was back in the day when they used mores, and only limited voice.
30west on Feb 16, 2016
I remember it as carrier and modulation when I,m responding : )
Vincent on Jan 18, 2017
although that is well stipulated in the military book it has not been adopted by ICAO and hence 5*5 in itself is an error in radiotelephony. ICAO only established readability scales and not signal strengths
Mv on Dec 28, 2017
5×5 = 25. This is the # of combinations you can have in your report based on # for readabilty x # for strenght. Nowdays none bother and use the 1st # as a comaparasion scale to the 2nd Sort of like your engine compression check i.e. 77/80
coletrain489@gmail.com on Feb 07, 2018
Aw nice..my stupid contract placement phone almost won. Excellent..or should i say 5×5..splendid..zzz…Cole the hibernating beast..frozen Canada☺
Robert Perry on May 23, 2018
Here is another way to use this. 5 by 5 has been used in the military. Ham operators use this: http://www.acsu.buffalo.edu/~maxwell/RSTInfo.html
Walter M Henriques on Jun 13, 2018
Yes..very interesting! In Alien’s, the military spacecraft pilot acknowledged the same “five by five” while descending to the hostile planet. Internet wasn’t online yet, but no I know..thanks
sky on Mar 30, 2019
Five by five doesn’t mean anything in aviation. The proper term for responding to a properly functioning transmission is “Loud and Clear.” It’s published in the P/CG so everyone can be on the same page with regard to meaning. Five by five is not published in any aeronautical publication and it doesn’t make one sound cool so put that away in the closet where it belongs.
gas on Apr 09, 2019
LOL all these numbers are nonsense and no one knows what they mean. That’s why the military uses plain language prowords.
examples
RADIO CHECK
LOUD AND CLEAR
GOOD AND READABLE
LOUD BUT UNREADABLE
WEAK AND INTERMITTENT
Get with the program “CFIs”
https://en.wikipedia.org/wiki/Plain_language_radio_checks
davidw963 on May 02, 2019
Industry Canada (formerly Transport Canada) guidance on radio checks as per Radiocom Information Circular 21 section 5.7.5 (the study guide if you want to get a restricted operators certificate with aeronautical qualification).
Readers Digest version: Signal Strength only on a 1-5 scale. I do remember the classic “5×5” strength and readability from my military days, but they work on their own nets and procedures outside of TC aviation regs.
5.7.5 Signal (or Radio) Checks
When your radio station requires a signal (or radio) check, follow this procedure:
Call another aircraft or aeronautical ground station on any appropriate frequency that will not interfere with the normal working of other aircraft or ground stations, and request a signal check.
The signal check consists of “SIGNAL (or RADIO) CHECK 1, 2, 3, 4, 5. HOW DO YOU READ ME? OVER.”
Your station identification (call sign) should also be transmitted during such test transmissions.
Signal checks should not last more than 10 seconds.
When replying or receiving a reply to a signal check, the following readability scale should be used:
Bad (unreadable)
Poor (readable now and then)
Fair (readable but with difficulty)
Good (readable)
Excellent (perfectly readable)
Communications checks are categorized as follows:
Signal check – If the test is made while the aircraft is airborne.
Preflight check – If the test is made prior to departure.
Maintenance check – If the test is made by ground maintenance.
Example: WATSON LAKE RADIO
THIS IS
CESSNA FOXTROT ALFA BRAVO CHARLIE
REQUEST SIGNAL CHECK ON FIVE SIX EIGHT ZERO
CESSNA FOXTROT ALFA BRAVO CHARLIE
THIS IS
WATSON LAKE RADIO
READING YOU STRENGTH FIVE
OVER
agkcrbs on Mar 26, 2020
In the 1967 Apollo 1 recording, the pilots threw a variety of signal confirmations, each seeming to prefer his own: “Loud and clear”, “five square”, and “five by five”. They definitely sounded cool.
John on Oct 05, 2020
So am I to understand, then, that it’s “CLEAR AND LOUD!” as compared to “LOUD AND CLEAR!”
I don’t know why but that makes me a little happy. It isn’t uncommon for a one off to be easier to remember than something that follows an expected norm.
Dennis on Oct 05, 2021
I used to run radio checks on my base in Vietnam….. every hour all night
The abreviated answer to a radio check was…”I have you 5 by”
That was it…very short… very quick
Sgt Rock on Apr 09, 2022
As a communicator in the U.S. Marines we would say I have you Lima Charlie (loud and clear) .
Example: Hotshot hotshot, this is hotshot8 radio check over…Roger hotshot 8, this is hotshot, I have you Lima Charlie….or weak but readable or unreadable etc.
So although old navy CW would use the 1-5 system starting with readability followed by signal strength, we did the opposite and did signal strength followed by readability. As radio operators we were also trained in CW in my recon unit, to be able to contact the navy on HF as a backup. Interestingly enough it was also to be used in case of nuclear war and the loss of satellite comms.
Roxy W on Jun 24, 2023
Many commenters have different explanations of which number of the two means what. So, I’m going to go with the expression “loud and clear.” 1st number being signal strength and the second beings clarity.
Tango on Jan 05, 2024
I was a Marine Corps Aviator (AKA Naval Aviator), and we were specifically trained never to use “5×5” in any radio communication because it is considered to be unprofessional nonsense.
In fact, we were strictly directed never to use it by our instructors during Aviation Pre-Indoctrination (API) in Pensacola, Florida, which is basically Naval Aviation Ground School, because it is unclear, confusing, non-standard, and does not appear in any official publication or guidance.
Military aviation certainly does not use this terminology in actual communications or training, at least not in my experience.
Also, if you want to meet the basic aviator requirement of sounding cool and competent on the radio, you would never say it in aircraft communications. You would instead say something more like, “Loud and Clear Oceanic, Sumo 723 Out.”