# How can multiple airplanes prevent simultaneous communication between ATC?

If two planes try to talk at the same time, do you hear nothing or both? Let's say ATC clears someone to land and they read back. I wait 4 seconds and then ask them something, how do I know another aircraft won't ask something at the same time?

As you fly more you will get to know the flow of radio transmissions and be able to identify when another exchange has completed. This comes with time and needs to be learned over time, it may be beneficial to listen into things like liveATC in your spare time to get comfortable. The FAA has a nice little brief on it here with some good pointers:

Listen before you transmit. Many times can get the information you want through ATIS or by monitoring the frequency. Except for a few situations where some frequency overlap occurs, if you hear someone else talking, attempting to transmit will be futile. You will probably jam ("step on") someone else's attempt to transmit, causing a need to repeat the call. If you have just changed frequencies, first pause and listen to make sure the frequency is clear.

Think before keying your transmitter. Know what you want to say and, if it is lengthy, (e.g., a flight plan or IFR position report), jot it down so you do not waste transmission time trying to remember what you need to say.

A solid 1-3 second pause should ensure the channel is free for you to transmit. The nature of transmissions is to keep them short and to the point, even on a busy frequency you will have plenty of time get in what you need and get a response.

As for the multiple transmissions at once, you will know! When two people attempt to transmit at the same time a nasty noise occurs. This is addressed here.

• 6-8 sec is a very long time. A busy stretch at a local field (class D) can require 1-2sec timing. – acpilot Mar 29 '18 at 4:58
• @acpilot agreed I have updated, after counting it out in my head 8 seconds is longer than I had in mind when writing this. – Dave Mar 29 '18 at 5:09
• One thing I wanted to add is that "trying to get a word in" is absolutely a problem on a busy frequency, as are people using excessively long calls. It's one of the reasons I think using proper phraseology and being concise is so important. Sometimes it's just sheer volume of traffic though, and there's little you can do apart from work around it – Dan Mar 29 '18 at 11:42
• As for the multiple transmissions at once, you will know! Everyone on frequency will hear the nasty noise except for the two people transmitting – TomMcW Mar 29 '18 at 23:45
• Typically thats followed up with a very brief scolding from the controller... – Dave Mar 30 '18 at 4:14