Which part outlines airworthiness standards for transport category airplanes?

The correct answer is Part 25, which specifically outlines the airworthiness standards for transport category airplanes. This part of aviation regulations establishes the requirements that these aircraft must meet to ensure their safety and performance capabilities. It covers aspects such as structural integrity, flight performance, and system reliability, which are crucial for the classification of an aircraft as a transport category airplane.

Part 23, on the other hand, pertains to the airworthiness standards for small airplanes, which do not fall into the transport category. Part 27 and Part 29 focus on rotorcraft, with Part 27 detailing the standards for normal category rotorcraft and Part 29 addressing the standards for transport category rotorcraft. Therefore, these parts are not applicable to transport category airplanes and do not provide the relevant airworthiness standards that Part 25 encompasses.