Do you know what the phrase "on guard" really means?

A common and feared phrase in the Infinite Flight world is the “on guard” phrase. Everyone knows what it means, but does anyone actually know why it’s called “on guard”?

In the real world, all nearby stations have a unique frequency that they transmit on. However, some frequencies are reserved. The most popular one is the “unicom” frequency (122.8 MHz). However there is one more that is not so well known to non-pilots – the guard frequency.

The guard frequency (121.5 MHz) is a frequency reserved for emergency transmissions. Some airlines are required to monitor the guard frequency in cruise, in case someone is in trouble (this is often done on VHF 2, the secondary radio channel).

This means that a lot of aircraft listen to this frequency at all times. Sometimes in real life, ATC can encounter a scenario IF ATC’s deal with a lot. An airplane is in or near your airspace, but not on your frequency. A solution to that is that the controller can try to contact the airplane via the guard frequency. To let everyone know that it is a transmission from the guard frequency, they can sometimes start the transmission with something like this:

“Delta 2 6 Tango Foxtrot, Atlanta Center on guard, contact me on 134.80”

This can also be done, and actually has been done in the case of a pilot having a stuck mic.

Now you know what the phrase really means! :)


That was really interesting, thank you so much!


i keep on learning more stuff every day, besides school :)


For extra credit, what is the UHF guard freq?


Thank you. Glad you out this up mate

“You have a GREAT day!”. LOL :D

That’s MAD ;)

243.0 MHz sir! :)

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Really helpful thanks

@Mats_Edvin_Aaro… Good call Mats. Just a sideline, All Tactical military aircrew wear a survival vest loaded with junk. Among that junk is a V/UHF Portable Radio with 2 channel settings. I is pre- programmed to Guard
the other tunable usually to ResCap or a discrete command net. Max

(The Guard frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD) or VHF Guard, and 243.0 MHz for military use, also known as Military Air Distress (MAD) or UHF Guard.) (multiple sources)

(Loved that Hot Key Video)


Ultra High Frequency

Tssk tssk pretty sure @THE-OP knows what that is… :P He asked me if I knew what the freq was ;)


😂 you’re funny 😏. Great post @Mats_Edvin_Aaro I came across that in my PPL studies and thought it was pretty interesting.

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Haha, these stuck mic incidents are so funny. Check out the Southwest Stuck mic, pretty hilarious.

I was gonna link to that, but that wasn’t really appropriate in a forum like this, HAHA… :P

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Yea im glad you didn’t lol

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Fantastic thread as always my friend, thank you!

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I read on this just awhile ago too, was curious what on guard actually meant.

One time i read, an airline was hot on frequency without knowledge and atc was spamming on guard because they were too busy having the conversation of their life.

Great job Mats! Very helpful! Also loved the video ;)

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Oh Yeah, that was a hot topic a while ago.

What does that number that he was given do?