Operations Over People and Moving Vehicles

Prior to 2021, small unmanned aircraft (sUAS) operations over people were generally prohibited unless the individuals were directly involved in the flight (e.g., the Remote Pilot in Command (PIC), person manipulating the controls, or a Visual Observer), or were covered by a protective structure or stationary vehicle. Beginning in 2021, the FAA introduced new categories of drones, each with its own set of privileges for operating over people and, under certain conditions, over moving vehicles.

Four Categories of Drones

Under the updated rules, sUAS are grouped into four categories based on their weight and potential kinetic energy upon impact:

1. Category 1: Drones weighing less than 0.55 pounds (250 grams).
2. Category 2: Drones with an impact energy of up to 11 foot-pounds.
3. Category 3: Drones with an impact energy of up to 25 foot-pounds.
4. Category 4: Drones requiring an FAA airworthiness certificate (heavier and more complex systems).

How Drone Categories Are Defined

The underlying principle behind the four drone categories introduced by the FAA is based on the amount of kinetic energy that a drone could impart if it were to collide with a person. Kinetic energy (KE) is a measure of how much energy an object in motion has. In simple terms, kinetic energy depends on two factors:

    Mass: How heavy the drone is.

    Velocity: How fast the drone is traveling.

The mathematical formula for kinetic energy is:

where:

    m is the mass of the drone, and

    v is the velocity (speed) of the drone.

Both mass and velocity play critical roles. Even a relatively light drone can generate significant kinetic energy if it travels fast enough. Conversely, a heavier drone at a lower speed might produce a similar amount of kinetic energy. The FAA uses kinetic energy thresholds to define Categories 2 and 3 because it provides a flexible way to classify drones based not only on their inherent characteristics (like weight) but also on how operators actually fly them (their speed and altitude).

Why does altitude matter?

Altitude indirectly affects kinetic energy because a drone that loses power or has a mechanical failure while flying high has more time and distance to accelerate toward the ground before impact. If the drone were operating at a higher altitude, gravity would cause it to gain speed as it falls, thereby increasing its kinetic energy upon impact.

In essence, the category is not just about how heavy the drone is when it’s resting on the ground, but also the conditions under which it is operated—its speed, altitude, and flight profile all influence how much damage it could do if something goes wrong.

Why and How Could a Single Drone Qualify for Multiple Categories?

A single drone can potentially operate in different categories depending on how the pilot chooses to fly it. Since Categories 2 and 3 are defined by a maximum allowable kinetic energy at impact rather than just a fixed weight, the pilot has flexibility. Here’s how that could work:

Same Drone, Different Flight Profile:

Consider a drone with adjustable flight settings—perhaps it can fly very fast at high altitudes, or it can be restricted to slower speeds and lower altitudes. If the pilot plans to operate the drone at a slower speed and keep it closer to the ground, the maximum potential kinetic energy in a crash scenario is lower. Under these “low and slow” conditions, the drone might not exceed the kinetic energy limit for Category 2, making it eligible to operate under that category’s more flexible rules.

On the other hand, if the same drone is operated at higher speeds or altitudes, it could generate more kinetic energy in a fall. In that “faster and higher” mode of operation, the drone could exceed Category 2’s energy threshold and fall into Category 3, which comes with more stringent restrictions.

Pre-Flight Decision and Compliance:

Before each flight, the pilot must decide under which category the drone will be operated. This decision effectively sets the operational limits—such as maximum allowable speed or altitude—to ensure the drone remains within that category’s kinetic energy constraints. Once the flight begins, the pilot must adhere to these predetermined limits for the entire flight to remain compliant.

 For example, the pilot might say: “Today I’m going to operate this drone under Category 2 rules.” To do that, the pilot will restrict how fast and how high they fly so the drone cannot surpass the 11-foot-pound kinetic energy limit. If the pilot wanted to operate with fewer speed/altitude restrictions, they could choose Category 3—accepting that under Category 3 rules, they cannot perform sustained operations over open-air assemblies of people.

Requirements by Category

• Category 1 (Less than 0.55 lbs):
  • No exposed rotating parts that could lacerate human skin.
  • May conduct transient flight over people.
  • Sustained flight over open-air assemblies of people is allowed if the drone is equipped with Remote Identification (Remote ID).
• Category 2 (Up to 11 ft-lbs kinetic energy):
  • No exposed rotating parts that would lacerate human skin.
  • No safety defects, and must have an FAA-accepted Means of Compliance (MOC) and Declaration of Compliance (DOC) from the manufacturer.
  • Sustained flight over open-air assemblies is permitted with Remote ID.
• Category 3 (Up to 25 ft-lbs kinetic energy):
  • No exposed rotating parts that would lacerate human skin.
  • No safety defects, and must have FAA-accepted MOC and DOC.
  • May not conduct sustained flight over open-air assemblies.
  • May only operate over people in a restricted-access area where all participants are on notice that a drone is flying overhead.
  • Transient flight over people not involved in the operation is not allowed unless within these closed-access conditions.
• Category 4 (Airworthiness Certificate Required):
  • Must hold an FAA airworthiness certificate.
  • Must operate according to the FAA-approved flight manual and adhere to all listed operating limitations.
  • Operations over people will be governed by the conditions specified in the airworthiness certification and associated documentation.

Operations Over Moving Vehicles

For drones in Category 1, 2, or 3:  The new rule permits transient flight over moving vehicles, provided it is not a sustained operation. For sustained flight over vehicles, the operation must occur within a restricted-access area and all individuals must be made aware of the drone’s presence.

For drones in Category 4: The aircraft must be operated in accordance with the operation limitations laid out in the FAA Approved Flight Manual for that aircraft.

In Which Category Is My Drone?

Small drones: If your aircraft weighs less than 0.55 pounds, it is in Category 1.  Remember that even though it’s less than 0.55 pounds, Remote ID is still required for flight over people.

Large drones: For flights over people, if your aircraft exerts 25 foot-pounds of kinetic energy on impact or more, the aircraft must have an airworthiness certificate issued by the FAA under Part 121 and must be operated in accordance with the operating limitations specified in the FAA-approved Flight Manual.  Obtaining a Part 121 airworthiness certificate is a long and expensive process.  Most readers of this book will not be flying drones in this category.

Medium size drones - categories 2 and 3: These are where typical “prosumer”-grade drones, such as the DJI Mavic, fall.  The FAA’s UAS Declaration of Compliance website, https://uasdoc.faa.gov/listDocs, includes a list of aircraft that meet the requirements of Categories 2 or 3.

Means of Compliance and Declaration of Compliance

To fly a drone under Category 2 or 3 rules, the manufacturer must submit and the FAA must accept a Means of Compliance (MOC) for that drone.  An MOC is a method to show that a small unmanned aircraft does not exceed the applicable injury severity limit upon impact with a human being, does not contain any exposed rotating parts that would lacerate human skin, and does not contain any safety defects.

Once the MOC is complete, the manufacturer then submits to the FAA a Declaration of Compliance (DOC).  If the FAA determines the manufacturer demonstrated compliance with Category 2 or 3, it will accept the DOC and add it to the list on the UAS Declaration of Compliance website at https://uasdoc.faa.gov/listDocs.