§ 61.3 Requirement for certificates, ratings, and authorizations.

(a) Pilot certificate. A person may not act as pilot in command or in any other capacity as a required pilot flight crewmember of a civil aircraft of U.S. registry, unless that person—
(1) Has a valid pilot certificate or special purpose pilot authorization issued under this part in that person's physical possession or readily accessible in the aircraft when exercising the privileges of that pilot certificate or authorization. However, when the aircraft is operated within a foreign country, a current pilot license issued by the country in which the aircraft is operated may be used; and some other stuff like picture ID that doesn't affect the answer.

(b) Required pilot certificate for operating a foreign-registered aircraft. A person may not act as pilot in command or in any other capacity as a required pilot flight crewmember of a civil aircraft of foreign registry within the United States, unless that person's pilot certificate:
(1) Is valid and in that person's physical possession, or readily accessible in the aircraft when exercising the privileges of that pilot certificate; and
(2) Has been issued under this part, or has been issued or validated by the country in which the aircraft is registered.


Sounds like you would have to operate inside the appropriate airspace.