14 CFR 21.171 : Aeronautics And Space (§ 1.1 To Parts 1311-1399) — (§ 1.1 To Parts 50-59) — Federal Aviation Administration, Department Of Transportation (§ 1.1 To Parts 50-59) — Aircraft (§ 21.1 To Parts 50-59) — Certification Procedures For Products And Articles (§ 21.1 To § 21.700) — Airworthiness Certificates (§ 21.171 To § 21.199) — Applicability.