Which CFR part establishes airworthiness standards for transport category airplanes?

• A. Part 25
• B. Part 27
• C. Part 29
• D. Part 39

Answer: (A)

Part 25 sets the airworthiness standards for transport category airplanes, meaning the large airplanes used for commercial passenger and cargo service. It specifies what those airplanes must be designed, built, and tested to do—covering structure, performance, systems, equipment, and safety features—and it defines how certification is demonstrated to prove they meet those safety requirements.

The other parts apply to different aircraft or purposes: rotorcraft have their own standards for large helicopters, and airworthiness directives (Part 39) are mandatory safety actions issued after issues are found in existing airplanes, not the design standards themselves. So for establishing airworthiness standards for transport category airplanes, Part 25 is the correct reference.