Aircraft operator (EASA)
What means “Operator”?
The word “Operator” is not defined in EU law (EASA), neither in 178/2011 or Regulation 145 nor in 216/2008.
That means that the general definition applies as “any legal or natural person, operating or proposing to operate one or more aircraft”, more precisely “the person or company organizing a flight under its operational control”.
The operator is in charge to prepare flights (NOTAM, MET reports, flight plans), to get the necessary PPR/slots and to pay the expenses as landing taxes, handling, fuel, etc.
It is also responsible to monitor the aircraft’s maintenance, insurances and airworthiness statement.
Things are clear: The “operator” does not have to be the same person as the pilot-in-command!
While this is usually the case when filed in an ICAO flight plan (OPR/PVT) in non-commercial flight operations, nothing precludes a different situation: an “N” aircraft operated by USA operating company, for a private flight, with a European natural person as pilot-in-command with a valid FAA certificate.
In fact, EU law 216/2008 distinguishes expressly the definition of “pilot” and “operator”.
The importance is that the pilot will consider his company as the only organizer of their (instrument) flights.
If this is the case, his company will be considered as a valid foreign (USA) operator.
In this case you are flying legally an USA operated aircraft with a USA registration in Europe with a FAA certified pilot certificate. That the pilot in command is a European, an American, Russian or Japanese etc. makes no difference.