14 CFR 65.123: Additional type ratings: Requirements.

A certificated parachute rigger who applies for an additional type rating must—

(a) Present evidence satisfactory to the Administrator that the applicant has packed at least 20 parachutes of the type for which the applicant seeks a rating, in accordance with the manufacturer's instructions and under the supervision of a certificated parachute rigger holding a rating for that type or a person holding an appropriate military rating; and

(b) Pass a practical test, to the satisfaction of the Administrator, showing the applicant's ability to pack and maintain the type of parachute, appropriate to the type rating sought. To pass the practical test for an additional type rating, the applicant must satisfactorily demonstrate the objectives in the area of operation specified in the Parachute Rigger Practical Test Standards (incorporated by reference, see § 65.23), applicable to the type rating sought.