Whenever a material, part, process, or appliance is required to be approved under this chapter, it may be approved --

(a) Under a Parts Manufacturer Approval issued under §21.303;

(b) Under a Technical Standard Order issued by the Administrator. Advisory Circular 20-110 contains a list of Technical Standard Orders that may be used to obtain approval. Copies of the Advisory Circular may be obtained from the U.S. Department of Transportation, Publication Section (M-443.1), Washington, D.C. 20590;

(c) In conjunction with type certification procedures for a product; or

(d) In any other manner approved by the Administrator.

[Amdt. 21-38, 37 FR 10659, May 26, 1972, as amended by Amdt. 21-50, 45 FR 38346, June 9, 1980]