14 CFR § 119.33

A person may not operate as a direct air carrier unless that person—

Is a citizen of the United States;

Obtains an Air Carrier Certificate; and

Obtains operations specifications that prescribe the authorizations, limitations, and procedures under which each kind of operation must be conducted.

A person other than a direct air carrier may not conduct any commercial passenger or cargo aircraft operation for compensation or hire under part 121 or part 135 of this chapter unless that person—

Is a citizen of the United States;

Obtains an Operating Certificate; and

Obtains operations specifications that prescribe the authorizations, limitations, and procedures under which each kind of operation must be conducted.

Each applicant for a certificate under this part and each applicant for operations specifications authorizing a new kind of operation that is subject to § 121.163 or § 135.145 of this chapter shall conduct proving tests as authorized by the Administrator during the application process for authority to conduct operations under part 121 or part 135 of this chapter. All proving tests must be conducted in a manner acceptable to the Administrator. All proving tests must be conducted under the appropriate operating and maintenance requirements of part 121 or 135 of this chapter that would apply if the applicant were fully certificated. The Administrator will issue a letter of authorization to each person stating the various authorities under which the proving tests shall be conducted.