It comes from Article 4 of the Basic Regulation. This defines the applicability of the EASA regulations, including FCL. They are applicable to an aircraft "registered in a third country and used .... by an operator established or residing in the Community".
The residency of the operator is the key point. If the Operator is outside the EU, then clearly there can not be a requirement for complying with EASA FCL (eg. a foreign airline or corporate jet flying into the EU), nor can they apply to a foreign operater even if the crew are EU residents (for example, a non-EU airline with crews based in the EU).
So, someone resident in the US can fly their N-reg airplane into Europe. They can even pay an EU resident with FAA certificates only to fly it. But if the operator is resident in the EU, the crew must have EASA FCL licenses. The debate is whether you could consider the US Trust to be the operator of an EU resident's aircraft. If so, the EU resident wouldn't need to comply with EASA FCL. My point is that in the conventional way EU private pilots fly their N-reg airplanes, they (not the Trust legal owner) are the Operator.
brgds
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