I know of the transponders used for communication by Air Traffic Control, but apart from that, what radio equipment do pilots use to talk to ATC? What modulation method is used?

  • $\begingroup$ Welcome to aviation.SE! This seems like quite a broad question, you might like to read through some of our existing radio questions and see if you can be more specific. For information on frequencies, see this question. $\endgroup$
    – Pondlife
    Apr 9, 2018 at 14:01
  • $\begingroup$ Also related, maybe even a dupe? $\endgroup$
    – Pondlife
    Apr 9, 2018 at 14:16

4 Answers 4


emphasis added

As of 2012, most countries divide the upper 19 MHz into 760 channels for amplitude modulation voice transmissions, on frequencies from 118–136.975 MHz, in steps of 25 kHz.

A typical plane often has two communication radios, referred to as COM1 and COM2.
Each radio has an active and standby frequency. The pilot can listen to either radio, or both radios at the same time, but can only broadcast on a single radio.

There are often 2 navigation radios as well, NAV1 and NAV2, which can be tuned to VORs or other radio beacons, and the pilot can listen on those radios (typically for Morse Code IDs, Recorded Voice broadcasts, and occasionally, Voice-over-VOR ATC)


The major communication tools are obviously Vhf radios for voice, another one is HF, particularly in remote place or oceanic. In tran atlantic the voice comms are thru HF with SELCAL( selective call) which brings another communication tool more and more used : CPDLC( controller pilot datalink communications) this one is not by voice. Clearances or requests are given by this method certainly for transatlantic and more and more in land as well.


A short summary, specific to the US:

VHF AM is the most common voice mode for communications with ATC.

UHF AM is also used for military and some government services, but generally just military, for communication with ATC.

HF radio is used for communications with ATC, and is most often used on oceanic routes. It is not as "reliable" as VHF, but the signals will propagate farther.

Other enhancements and other modalities are available but they are not strictly voice communications.

14 CFR 87 covers aviation services, and defines frequencies and modes as well as uses for aviation specific services.



This is a very broad question just because every type of aircraft has different requirements for its design purpose. As civil aircraft may not need to use UHF frequencies where some military aircraft must have an UHF radio. And transponders are not used for communication. :)

  • $\begingroup$ Transponders ARE used for communication: When you press IDENT and the controller responds, that is communication. When you change your squawk code or Transponder mode, and the controller sees it, that is communication. Not all communication is Voice. $\endgroup$
    – abelenky
    Apr 9, 2018 at 17:18
  • 1
    $\begingroup$ Hmm, you are right. But as far as I understand, @joey asks about radio telecommunication. I mean two-way-communication. Not identification or telling ATC that you are in Emergency over transponder not over radio. $\endgroup$ Apr 9, 2018 at 18:42
  • $\begingroup$ ICAO Doc 8168 Vol 1, page 245 and others depicts how transponders will be used in case of COMMUNICATION FAILURE. I am still looking for other documents supporting that transponder is not a Communication device. Its used for Identification. [link] (chcheli.com/sites/default/files/icao_doc_8168_vol_1.pdf) $\endgroup$ Apr 9, 2018 at 19:20
  • $\begingroup$ FAA Handbook. Page 55. (faa.gov/regulations_policies/handbooks_manuals/aircraft/…) “verbal communication” and transponders. I got a -1 , no problem. :) I am still looking for Documents. And will wait an answer from @joey. $\endgroup$ Apr 9, 2018 at 21:28
  • $\begingroup$ (whispering) I am not arguing with myself. This helps me read more. That’s all. :) $\endgroup$ Apr 9, 2018 at 21:31

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