Certifying aircraft is a long and expensive process. So generally speaking, aviation authorities 'share the burden' by relying on each other. By the same toke

Certifying aircraft is a long and expensive process. So generally speaking, aviation authorities 'share the burden' by relying on each other. By the same token, the FAA will take an EASA certification of an Airbus aircraft as valid without much additional checking. FAA's reputation alone was good enough for other aviation authorities to accept its certification of Boeing's MAX 8, which is why the FAA matter despite happening way outside its jurisdiction.