Each applicant for a mechanic certificate or rating must present either—

(a) An authenticated document from a certificated aviation maintenance technician school in accordance with § 147.21 of this chapter; or

(b) Documentary evidence, satisfactory to the Administrator, of—

(1) At least 18 months of practical experience with the procedures, practices, materials, tools, machine tools, and equipment generally used in constructing, maintaining, or altering airframes or powerplants, appropriate to the rating sought; or

(2) At least 30 months of practical experience concurrently performing the duties appropriate to both the airframe and powerplant ratings.