14 CFR 47.3: Registration required.

(a) An aircraft may be registered under 49 U.S.C. 44103 only when the aircraft is not registered under the laws of a foreign country and is—

(1) Owned by a citizen of the United States;

(2) Owned by an individual citizen of a foreign country lawfully admitted for permanent residence in the United States;

(3) Owned by a corporation not a citizen of the United States when the corporation is organized and doing business under the laws of the United States or a State within the United States, and the aircraft is based and primarily used in the United States; or

(4) An aircraft of—

(i) The United States Government; or

(ii) A State, the District of Columbia, a territory or possession of the United States, or a political subdivision of a State, territory, or possession.

(b) No person may operate an aircraft that is eligible for registration under 49 U.S.C. 44101-44104, unless the aircraft—

(1) Has been registered by its owner;

(2) Is carrying aboard the temporary authorization required by § 47.31(c); or

(3) Is an aircraft of the Armed Forces of the United States.

(c) Governmental units are those named in paragraph (a) of this section and Puerto Rico.