Which FAR part governs commercial pilot certificates?

The regulation that governs commercial pilot certificates is found in FAR Part 61. This part specifically outlines the certification requirements, privileges, and limitations for all pilots, including commercial pilots. It details the necessary flight training, aeronautical experience, knowledge tests, and proficiency checks that an individual must complete to obtain a commercial pilot certificate.

In contrast, FAR Part 91 pertains to general operating and flight rules applicable to all aircraft operations, while FAR Part 141 outlines the requirements for pilot schools that provide structured training programs. FAR Part 121 governs the operation of scheduled air carriers, focusing on commercial airline operations and their specific regulatory requirements. Thus, the clear focus of FAR Part 61 on pilot certification, including the detailed framework for obtaining a commercial pilot certificate, makes it the correct answer for this question.