How does a commercial pilot differ from an airline transport pilot (ATP)?

The distinction between a commercial pilot and an airline transport pilot (ATP) primarily revolves around the privileges and responsibilities each certification provides.

An ATP is specifically designed to allow the holder to serve as the pilot-in-command (PIC) for scheduled airlines. This certification involves a more extensive knowledge base and experience, as ATP holders must demonstrate a higher degree of proficiency and a greater understanding of regulation surrounding airline operations. The ATP certificate is a higher level of pilot certification compared to that of a commercial pilot, which allows for various types of flying but does not permit the holder to act as PIC in scheduled commercial airline operations.

While commercial pilots can engage in a variety of activities, such as flight instruction or flying cargo, they lack the authority to act as captain on scheduled airline flights unless they hold an ATP. This difference makes option C the correct answer, as it precisely identifies the unique capability conferred upon ATP holders that is not available to commercial pilots.