Flying a drone directly over a person is not something Part 107 leaves to your judgment, and the rule arrives in two layers. The prohibition is § 107.39: no person may operate a small unmanned aircraft over a human being unless that person is directly participating in the operation, is located under a covered structure, or is inside a stationary vehicle that can provide reasonable protection from a falling aircraft — or unless the operation meets the requirements of at least one of the operational categories in subpart D. The first three exits turn on who the person is and where they are standing, and need no category and no paperwork at all. The fourth is subpart D, and § 107.105 is its gate: except for those § 107.39 cases and the separate moving-vehicle rule at § 107.145, a remote pilot in command may conduct operations over human beings only in accordance with Category 1, 2, 3, or 4. That is the sentence that makes the categories matter, and which one you may use is decided entirely by the aircraft you fly and what its maker has shown about it.

The four categories form a ladder built around one idea: how much harm the aircraft could do if it fell on someone. At the bottom, Category 1 asks only that the aircraft be light enough and free of parts that would cut. Categories 2 and 3 sit in the middle — heavier aircraft allowed over people only once a manufacturer has shown, through a formal declaration of compliance, that an impact stays under a set injury threshold measured in kinetic energy. Category 4 is the top of the ladder: aircraft that carry a full airworthiness certificate, the path for machines too large to meet the injury numbers of the other categories. The rungs rise in what the aircraft must prove, not in what you as the pilot may intend.

The practical consequence is that the category is a property of the aircraft, established before you ever fly it over anyone — and the next four sections take each category in turn, then the chapter closes on the separate rules for moving vehicles. Your job as remote pilot is to know which category your aircraft actually qualifies for and to fly within it, because the permission to be over a person comes from the aircraft’s proven safety, never from the operation looking routine.