> how would Turkey's s400 purchase be an article 8 violation?
This has been covered in the American refusal to sell Ankara F-35s and ensuing sanctioning of it under CAATSA [1].
In short, no detection system is perfect. And no modern military system is sold without servicing. Letting Russia service an air defence system with the privilege of painting NATO jets, arms and missile defences is a breach of trust. It could be considered, again, pettily, though good luck to those who claims the law is often anything but, “an international engagement in conflict with” Turkey’s NATO obligations.
