Finally, considerations on very light-weight UAS were completed during the FAA Registration Task
Force Aviation Rulemaking Committee in November/December 2015 (the “Registration ARC”).
The Registration ARC considered a paper by MITRE that looked at risks of small UAS impact to
people on the ground, based on assumptions in earlier studies. 6 That paper contains a graph of
probability of fatality vs. kinetic energy that was used to select an 80 J limit on kinetic energy as a
measure of potential lethality. This level of total kinetic energy, and a variety of assumptions, was
then used by the Registration ARC to calculate a weight threshold of 250 grams for registration.
With all of these factors in mind, because of the low level of risk of injury posed by flying objects
weighing 250 grams or less, the ARC recommends no performance-based standards be required for
unmanned aircraft in this category. The manufacturers will be required to indicate on the retail
packaging the actual flying weight, or a statement that the aircraft weight is less than 250 grams. To
provide flexibility in the future, the ARC does, however, recommend that the FAA inv ite industry to
create voluntary, non-binding standards for product marking of UAS weighing 250 grams or less to
make it clear to users that these UAS meet the requirement to operate over people.
4.1.2
Category 2 Performance Standards
Category 2 prescribes the performance standards and operational restrictions for operations over
people that are conducted by unmanned aircraft that weigh more than 250 grams, but still present a
1% or less chance of “serious” injury (AIS level 3 or greater) to a person in the event of impact. The
standard to determine whether the UAS meets the risk criteria will be an impact energy threshold
based on information presented to the ARC, and calculated by the FAA in J/cm². During its
meetings, the ARC was presented with information from Canada and the commercial space industry
suggesting that this calculation would result in a value of 12 J/cm2 and that a quadcopter UAS
weighing in the range of 4 to 5 pounds would qualify, depending on its design characteristics and
operating instructions. The ARC recommends that the FAA calculate this exact impact energy
threshold for the proposed flight-over-people rule.
For a small UAS to qualify for Category 2 operations, the manufacturer must certify that the UAS
does not, in the most probable failure modes, exceed the typical or likely impact energy threshold, in
accordance with industry consensus testing standards. The operator of the small UAS will also be
subject to certain operational restrictions, which are discussed below in Section 4.3.2.
To facilitate the development of industry consensus standards for Category 2 that are acceptable to
the FAA Administrator, the ARC recommends that the industry consensus standards must do the
following:
(1) Establish a test to measure the typical or likely impact energy of the small unmanned aircraft
in the most probable failure modes to determine whether it meets the specified impact
energy threshold. Testing may be subject to manufacturer defined operating limitations, if
any. The impact energy threshold used in the standards may account for the energy
“A New Paradigm for Small UAS,” Andrew Lacher and David Maroney, available at
https://www.mitre.org/sites/default/files/pdf/12_2840.pdf ; “Lethality Criteria for Debris Generated From Accidental
Explosions,” Jon Henderson, available at http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA532158.
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