Part 107 starts with a ban. Section 107.39 says you may not operate a small unmanned aircraft over a human being unless that person is directly participating in the operation, or is under a covered structure or inside a stationary vehicle that offers reasonable protection from a falling aircraft, or the operation fits at least one category in Subpart D. "Directly participating" means the crew, not the client standing on the sidewalk and not the crowd you were hired to film.
Subpart D, effective with the 2021 amendments, adds four categories. They are not weight classes you invent, and they are not waivers. If the aircraft and the operation meet the category, you do not also need a waiver for the mere fact of flight over people.
Category 1
Category 1 is the simple threshold in §107.110. The aircraft weighs 0.55 pounds or less on takeoff and throughout the operation, including everything on board or attached. It must not have exposed rotating parts that would lacerate human skin on impact. A 240-gram airframe can leave Category 1 when you add a strobe and prop guards that push it over 250 grams. Weigh the aircraft as it will fly.
Sustained flight over an open-air assembly still needs Remote ID, specifically §89.110 or §89.115(a), even for Category 1. Weight does not waive that condition. A brief transit is not the same as sustained flight over the crowd.
Categories 2 and 3
Categories 2 and 3 are not weight cutoffs. The aircraft must be eligible under a performance standard, listed on an FAA-accepted Declaration of Compliance, and labeled for that category.
Category 2, §107.120, requires that the aircraft will not cause an injury equal to or greater than the severity of 11 foot-pounds of kinetic energy from a rigid object, that it has no exposed rotating parts that would lacerate skin, and that it has no safety defects. The applicant, not the remote pilot at the field, submits the Declaration of Compliance. The remote pilot's job is to use a listed, labeled aircraft and follow the operating instructions. Section 107.115(b) adds the Remote ID condition for this category: no sustained flight over an open-air assembly unless the operation meets §89.110 or §89.115(a). Category 1 states the same condition in §107.110(b), and Category 4 states it in §107.140. Category 3 does not get that path.
Category 3 uses a higher injury threshold, 25 foot-pounds, in §107.130. The operating limits are stricter. Section 107.125 says the remote pilot must not operate over an open-air assembly. Over any person, the operation must be inside or over a closed or restricted-access site where everyone has notice, or the aircraft must not maintain sustained flight over a person unless that person is directly participating or sheltered in the §107.39 sense. A parade crowd does not become legal because you announce the flight on a loudspeaker. An open-air assembly is exactly what Category 3 forbids. Remote ID does not create a Category 3 exception for that crowd.
If a Category 2 or 3 label is damaged or missing, §107.135 says the remote pilot must relabel the aircraft in English, legibly and prominently, for the duration of the operation, identifying the correct category, before flying over people.
Category 4
Category 4 is the airworthiness path in §107.140. The aircraft has an airworthiness certificate issued under Part 21, is operated within the Flight Manual limitations, and those limitations do not prohibit operations over people. Maintenance and record rules in that section apply. An airline transport pilot certificate is not what makes an aircraft Category 4. Neither is a weight under 250 grams. That weight is Category 1.
Sustained flight over an open-air assembly in Category 4 again requires the Remote ID conditions in §89.110 or §89.115(a).
Moving vehicles and the waiver trap
Section 107.145 covers people inside moving vehicles. For Category 1, 2, or 3, the aircraft must remain over a closed or restricted-access site with notice, or it must not maintain sustained flight over the vehicle. Category 4 follows its Flight Manual. This is not the same rule as §107.25, which restricts operating the controls from a moving vehicle.
A flight that already meets §107.39 or a Subpart D category does not need a waiver for the over-people part. A waiver does not become necessary because the job is paid. If the aircraft does not meet a category and the people are not participating or sheltered, you do not fly over them. Remote ID compliance, by itself, is not a category. The Remote ID page keeps those records separate.