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ACARS messages are transmitted via radio just like normal ATC communications are. In the UK, for example, it is illegal to listen to and broadcast ATC chatter. Does the same apply to ACARS? If an ACARS message is sent from a ground station to an aircraft, say an ATC departure clearance, and I read it using a VHF receiver, would that be illegal? Can I share it online?

I understand the reason we can't find Live ATC for Canada, UK, Germany etc. is because of the local laws. But from what I can see these laws are related to voice transmissions, not text.

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As I'm sure you're aware, this portion of the Wireless Telegraphy Act is essentially unenforced for casual and personal airband scanning, with many airports, and air shows openly promoting and publicising their frequencies for enthusiasts.

However, I'm not at all sure where you've gotten the idea that the law refers to voice. There are two main elements of the Wireless Telegraphy Act to be aware of:

S.48:

https://www.legislation.gov.uk/ukpga/2006/36/section/48/enacted

A person commits an offence if, otherwise than under the authority of a designated person he uses wireless telegraphy apparatus with intent to obtain information as to the contents, sender or addressee of a message (whether sent by means of wireless telegraphy or not) of which neither he nor a person on whose behalf he is acting is an intended recipient

or

he discloses information as to the contents, sender or addressee of such a message.

As you can see, nothing in the act limits itself to voice, or even analogue communications. Ironically, if anything, the wording is anachronistic with the Telegraphy originating in the era of Morse transmissions but the legal intent is clear: Intercepting communications of any sort, not intended for you, is an offence. In fact, it is even clearer that it applies to ACARS than to voice, because, being a text-based protocol, ACARS is actually telegraphy, while voice radio is not for most purposes.

Either way, to clearly answer your question, ACARS and any other digital communication is covered identically under the act

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  • $\begingroup$ So in theory the ACARS messages needs to be coming from a ground station based from a country where these laws don’t exist? E.g. an aircraft flying in the US getting information about a UK airport. The ground station would be based in the US. $\endgroup$
    – user38116
    Nov 4, 2023 at 12:03
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    $\begingroup$ @user38116 Pretty sure it depends on where you are when intercepting the radio transmission, not from where it was sent or to whom it was intended. $\endgroup$
    – Bianfable
    Nov 4, 2023 at 15:52
  • $\begingroup$ Interesting, so you can intercept messages in Ireland for a message destined to a UK aircraft with information relating to the UK. I wonder how it would work in terms of ADSC, I assume it would work similarly. So if your satellite receiver is in Ireland then you’d be safe to intercept and share them. $\endgroup$
    – user38116
    Nov 4, 2023 at 18:44
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Related regulations are local, but are the implementation of obligations agreed by all member States of the International Telecommunication Union (ITU), an agency of the UN, so most countries have similar obligations, US might be a notable exception, in spite of being an ITU member.

For ITU, a radiocommunication is a communication by radio, and a communication is anything:

Any transmission, emission or reception of signs, signals, writings, images and sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems

Members have signed the Convention of the International Telecommunication Union which introduces the Radio Regulations (RR), RR say:

Secrecy
17.1 In the application of the appropriate provisions of the Constitution and the Convention, administrations bind themselves to take the necessary measures to prohibit and prevent:
17.2 a) the unauthorized interception of radiocommunications not intended for the general use of the public;
17.3 b) the divulgence of the contents, simple disclosure of the existence, publication or any use whatever, without authorization of information of any nature whatever obtained by the interception of the radiocommunications mentioned in No. 17.2.

So each member has to implement laws prohibiting the interception of radiocommunications, and the divulgence of the content, except for public broadcast.

Usually this is done be delivering licenses to authorized users or organizations, and establishing a general obligation of confidentiality for citizens, regarding communications for which they are not an authorized recipient. This is what UK does in the Wireless Telegraphy Act of 2006, as well explained by @Dan in his answer. In addition, Ofcom, the regulating body states:

Using spectrum without a licence or the benefit of an exemption, or in breach of the conditions of a licence or an exemption, is a criminal offence.

If you don't have a license to listen or transmit on the aeronautical frequencies, you are not allowed to listen. Listening and then disclosing the content is a breach of the general confidentiality obligation.

Note in EU (and possibly still in UK) scanners and receivers/transmitters for specific non-public bands can be sold, this is explicitly allowed by EU regulations, on the count of free circulation of goods.

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