Until April 21, 2021, a Part 107 pilot wanting to fly commercially over a crowd had exactly one path: apply for a waiver under § 107.39 and wait. The prior framework's blanket prohibition on flight above uninvolved people wasn't a risk calibration — it was a procedural bottleneck that treated a 200-gram toy and a 10-pound cinematic drone as equivalent hazards. The FAA's Operations Over People final rule, published January 15, 2021 (Federal Register docket 2020-28947) and effective April 21, 2021 (as corrected, 86 FR 13618, Mar. 9, 2021), pushed back from the originally published March 16 target, dismantled that bottleneck with a four-category system codified in 14 CFR Part 107 Subpart D. Categories 1 through 3 stratify access by how much kinetic energy the aircraft delivers to a body below. Category 4 takes a different route altogether: traditional airworthiness certification as a proxy for safety.

The Design Gate That Crosses Every Category

Before a single pound or foot-pound gets calculated, every aircraft operating over people under Categories 1 through 3 must clear one hardware requirement: no exposed rotating parts capable of lacerating human skin on impact, per § 107.110(a)(2) (Cat. 1), § 107.120(a)(2) (Cat. 2), and § 107.130(a)(2) (Cat. 3). Category 4 addresses the laceration constraint through Part 21 airworthiness certification. This is a design-intent gate, not an operational buffer. An open-frame propeller design fails it regardless of aircraft weight, pilot credentials, or claimed category. FAA guidance on means of compliance contemplates internally ducted fan configurations as one acceptable solution, provided that a typical ground-impact structural failure would not expose those elements. Operators and manufacturers who treat this as a box to check rather than a genuine constraint tend to discover the problem late in certification.

With that gate cleared, the framework stratifies access by injury risk. Category 1 covers aircraft at or below 0.55 pounds (250 grams) at takeoff with everything aboard. At that mass, kinetic energy on impact is low enough that the weight ceiling itself — combined with the no-laceration-parts requirement — constitutes acceptable risk. No manufacturer Declaration of Compliance is required; the remote pilot self-verifies before each flight. A qualifying Category 1 aircraft may overfly non-participating people without a waiver. The one meaningful restriction bites on sustained flight over open-air assemblies: that requires Remote ID compliance under § 89.110 (standard broadcast) or operation within a FAA-Recognized Identification Area under § 89.115(a).

The FAA's operational definition of "sustained" is worth reading carefully. Hovering above a crowd, flying back and forth across a gathering, or circling so the aircraft remains above some portion of it — all qualify. Per the rule's Federal Register preamble (86 FR 4314 at 4376, Jan. 15, 2021), a brief, one-time transit over a portion of an assembled gathering where the flight is unrelated to the assembly falls outside the restriction. A transit that crosses a crowd without dwelling over it is not sustained flight. Deliberate loitering above a summer festival without Remote ID active is.

The Kinetic Energy Ladder: 11 Foot-Pounds, Then 25

Category 2 accommodates aircraft heavier than 0.55 pounds, conditioned on a quantified impact ceiling: the aircraft must be designed, produced, or modified so that impact transfers no more than 11 foot-pounds of kinetic energy from a rigid object to a person below. The kinetic energy formula set out in the rule's Federal Register preamble (86 FR 4314, Jan. 15, 2021) and reflected in AC 107-2A — KEimpact = 0.0155 × w × v² — translates that ceiling into speed constraints by weight. A 1.0-pound aircraft cannot exceed roughly 26 feet per second (approximately 18 mph) at impact; a 3.0-pound aircraft is capped near 15 feet per second (approximately 10 mph). Manufacturers must account for terminal velocity in free fall, not cruise speed, when demonstrating compliance.

Unlike Category 1, Category 2 cannot be self-certified. The aircraft must carry an FAA-accepted Declaration of Compliance, be permanently labeled as Category 2 eligible, and ship with manufacturer-supplied remote pilot operating instructions. Compliance records must be retained for at least two years after the manufacturer ceases production. The open-air assembly access rule mirrors Category 1: sustained flight requires Remote ID compliance under § 89.110 or § 89.115(a).

Category 3 more than doubles the energy threshold to 25 foot-pounds — accommodating larger or faster platforms. The laceration prohibition, DOC requirement, permanent labeling, and manufacturer record-keeping obligations are identical to Category 2. The operational scope is not. Category 3 aircraft face an absolute prohibition on sustained flight over open-air assemblies. No Remote ID pathway unlocks this. Category 3 overflights of non-participants are lawful only in two narrow configurations: within a closed- or restricted-access site where all persons present have been notified that a drone may fly over them, or in configurations where the aircraft cannot by design maintain sustained flight above non-participants. Public outdoor events are structurally excluded at this energy tier, regardless of what technology the aircraft broadcasts.

Category 4, Remote ID, and What the Assembly Rules Actually Unlock

Category 4 exits the kinetic energy framework entirely. The aircraft must hold an airworthiness certificate issued under 14 CFR Part 21, and the remote pilot must operate within limits specified in the FAA-approved Flight Manual. If those limits prohibit operations over people or moving vehicles, the Category 4 designation does not override the restriction — the Flight Manual governs. Maintenance obligations are substantially heavier than in the lower tiers: work must follow the manufacturer's current maintenance manual, performed by qualified personnel, with records documenting all work completed, dates, technician names, life-limited part status, and airworthiness directive compliance. All of that documentation transfers with aircraft ownership. Category 4 trades the probabilistic kinetic energy approach for aviation's traditional design-and-maintenance-as-safety-assurance model. Its open-air assembly rule follows Categories 1 and 2: sustained flight requires Remote ID compliance under § 89.110 or § 89.115(a).

The OOP rule and the Remote ID final rule (Federal Register docket 2020-28948, also published January 15, 2021) are operationally coupled. September 16, 2023 was the mandatory Remote ID compliance date: any drone required to register must now broadcast its real-time location and control station location as a local radio signal — no internet connection required — unless flown exclusively within a FRIA.

Categories 1, 2, and 4 may conduct sustained flight over open-air assemblies only with Remote ID compliance. Category 3 has no pathway — the open-air assembly prohibition is absolute regardless of what technology the aircraft broadcasts.

That asymmetry is the sharpest edge of the OOP framework. Remote ID is not a master key to assembly airspace; it is an accountability mechanism the FAA deemed sufficient for lower-energy operations while explicitly withholding from the 25 foot-pound tier. The rule's architecture assumes that above a certain energy threshold, real-time identification doesn't change the outcome if something goes wrong.

A parallel conditional logic governs operations over moving vehicles under § 107.145. Before the OOP rule, overflying people in cars, on bicycles, or on scooters was prohibited without a waiver. The final rule opened a path for Categories 1, 2, and 3: the remote pilot must either operate within a closed- or restricted-access site where all vehicle occupants are on notice, or ensure the aircraft does not maintain sustained flight above moving vehicles. The vehicle definition is deliberately broad — bicycles, scooters, skateboards, cars, and trucks all qualify. Category 4 may overfly moving vehicles unless the Flight Manual specifically prohibits it.

The net result is a framework that gives commercial operators a legible decision tree where a waiver treadmill used to be. A Category 1 pilot with Remote ID active can overfly outdoor events. A Category 2 pilot with a DOC-compliant, permanently labeled aircraft and current operating instructions has equivalent access. Category 3 is where the rules bite hardest — no open-air assemblies, no exceptions, no technology workaround. What no category permits across the board: aircraft with exposed rotating parts capable of lacerating skin; any Category 3 aircraft over an open-air assembly; sustained flight over assemblies or moving vehicles outside a controlled, notified site without Remote ID on the tiers that permit it. Understanding which column of that table your aircraft and operation occupy is the practical starting point for any OOP compliance analysis.

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