Category 4 qualifies an aircraft in an entirely different way from Categories 2 and 3. Instead of a manufacturer’s declaration that an impact stays under a kinetic-energy threshold, a Category 4 aircraft must hold a full airworthiness certificate issued under Part 21 of the regulations — the same certification regime that governs crewed aircraft. This is the path for machines too large or too capable to meet the 11- or 25-foot-pound injury numbers of the other categories: rather than prove a low-energy impact, they are certified airworthy as aircraft in their own right, and § 107.140 lets that certification carry them over people.

With that certificate come obligations that echo crewed aviation. A Category 4 aircraft comes with an approved Flight Manual, and it must be operated within the operating limitations that Manual specifies — limitations that, for a Category 4 aircraft, must not themselves prohibit flight over human beings. And the airworthiness has to be kept up: § 107.140(c) places maintenance, preventive maintenance, alterations, and inspections on the owner — or on an operator who has agreed to take them on — performed by qualified persons and documented. Category 4 is therefore less a one-time qualification than an ongoing program: the aircraft is only eligible while its airworthiness is actively maintained.

One limit Category 4 shares with the lightest category is the rule for crowds. Under § 107.140(a), no remote pilot may hold sustained flight over an open-air assembly of human beings unless the operation also meets Remote ID under § 89.110 or § 89.115(a) — the same condition that binds Category 1. So even the most heavily certificated aircraft does not get a free pass over a crowd. What Category 4 buys is the ability to fly a larger aircraft over people at all; what it does not buy is exemption from the Remote ID bar that every over-people category raises at an open-air assembly.