What federal regulation defines the requirements for the issue of Type Certificates?

The requirements for the issuance of Type Certificates are indeed defined in FAR Part 21. This regulation outlines the procedures for obtaining Type Certificates for aircraft, aircraft engines, and propellers, along with the standards and processes that manufacturers must adhere to before their products are deemed airworthy. This part includes guidelines for the approval of designs, production, and continued airworthiness, ensuring that all aircraft meet the necessary safety and operational standards before they can be used in commercial and general aviation.

The other options refer to different aspects of aviation regulations. FAR Part 65 pertains to certification of airmen other than flight crew members, such as mechanics and repairmen. FAR Part 23 addresses airworthiness standards for normal, utility, acrobatic, and commuter category airplanes, focusing on their design and performance criteria. FAR Part 25 sets airworthiness standards for transport category airplanes, emphasizing performance and safety in larger aircraft. While all these parts play crucial roles in aviation safety, none specifically govern the issuance of Type Certificates like FAR Part 21 does.