In an interesting move Flarm made their over the air protocol public:
https://www.flarm.com/en/integration/flarm-famp-public-protocol/
This is very interesting, especially because they are part of the ADS-L coalition. I hope this will make it easier for all the traffic gadget companies to become interoperable. Good news for sure!
“FFPP is free to use for non-commercial applications that do not transmit FFPP radio packets, see the License Terms and Conditions. For commercial or extended use cases, a standardized license agreement is available – please get in touch with us.”
Meaning “Just call us and we will see how much money we think we can get from you”.
So you can build a FLARM receiver.
Has this not been previously possible and, if not, why not? I downloaded the document and see they use some 128 bit crypto
FTD_116_FLARM_FAMP_Public_Protocol_v1_01_pdf
I like this bit
4.2 Encryption and Decryption
The payload is partly encrypted to ensure message integrity, system safety and provide protection for the relevant content against eavesdropping, namely by article 3 of the Budapest Convention on Cybercrime and Directive 2013/40/EU.
They forgot the real reason 
The shared key is fixed and could have been obtained by disassembly of any receiving device.
Peter wrote:
Has this not been previously possible and, if not, why not?
The protocol was more or less out there anyway and there was nothing which could be done about it. Any change had to apply also to old hardware so the changes could be extracted frm the new binary files provided for the older devices anyway. So I assume they accepted this fact. To keep the momentum trying to make money with commercial projects and let the DIY projects do their thing it was published properly. Not a bad move I would say.
