Small UAS Over People: A New Safety Paradigm

By Frank Frisbie and Suzette Matthews Principals, Washington Progress Group LLC

FAA is taking the first significant step forward toward integration of UAS in the NAS.   By Notice published on February 13, 2019 is proposing to allow small UAS under stated conditions to fly over members of the public without a waiver.

Primary concern for people and property under the route of flight is new for FAA.  Historically, with manned aircraft taking off and landing on unpopulated airport facilities and operating mainly in transit mode under positive control over regular routings, death and injury to passengers and crews has been the main issue.  Injury and damage to persons and property on the ground have been statistically insignificant.   But, UAVs having no passengers or onboard crew, and flying random, often traversing or hovering routings over all manner of ground environments, their primary inherent safety concern is injury and damage to the general public on the ground.

The approach reflected in the new FAA NPRM is commendable.   It embodies safety paradigm innovations–most significantly the concept of certification/regulation by proffered safety cases, and performance rather than technical standards–that acknowledge and accommodate the unprecedented physical and operational characteristics, and great diversity of UAS.

In general, the NPRM recognizes the reality that very small UAS (Categories 1 and 2) are, or can be made relatively harmless in terms of potential injury to people and property on the ground, and if so can operate with an acceptable level of safety based solely on their physical properties.   As the aircraft increases in size and weight (as in Category 3) however, the potential increases for significant injury and damage to the public, and therefore precautions beyond physical innocuousness of the aircraft become necessary. The NPRM therefore proposes some operational conditions, namely that Category 3 UAS be prohibited from flying over open air assemblies of people, or if they do operate over groups of people, those people need to be in a closed area and informed that UAS will be overflying, or that the UAV either not perform sustained flight over them or that they be under a protective structure.

These measures seem to WPG reasonable for those Category 3 operators who are satisfied with restricting flights to unpopulated areas, or who are able and willing to control the ground environment over which they are flying.   But these conditions are too limiting for most commercial missions, which must operate to, from, and over populous open areas, and involve lingering or hovering, as well as traversing.

Therefore, moving forward from this small UAS NPRM, it’s time—past time–to establish and declare on what basis and under what conditions generally FAA will consider UAS flights over the non-participating public “acceptably safe.”  Experts, among them the authors, have recommended that FAA consider as “acceptably safe” those operations that can be performed at a level of accidents and mishaps already prevailing in the subject piece of airspace (Target Level of Safety (TLS)),  which it can be assumed the public already considers reasonably safe.  

Implementing this standard, a proponent for UAS operations should be required to proffer a two-part safety case.   First, the proponent should demonstrate reliability/integrity of its vehicle and operation equivalent to the prevailing TLS in that area.   But second, the safety case should also contain a plan for protecting the public from any harm or damage that might occur as a result of the operation.   This second element of the safety case would include: 1) a granular analysis and estimation of the environment, including population and property, overflown, (2) a showing that the operator has engaged to the extent possible in comparative route analysis and flight planning that minimizes the risk, and (3) that the operator is financially capable, or has in place an insurance vehicle adequate to compensate any third parties who are injured or damaged if the flight goes awry.    

FAA’s new rule requiring that the UAS registration be prominently displayed on the outside of the vehicle completes and enforces the protective construct by allowing any aggrieved member of the public to itself identify the offending aircraft and operator, and seek redress from any insurance coverage in place, or if necessary in court under legal tort liability principals.

In summary, the authors suggest that FAA is in already ready to propose a certification and operator-approval construct whereby UAS proponents can demonstrate an “acceptable” level of safety for flight over the general public based on currently prevailing TLSs, using state-of-the -art risk analysis and flight planning tools to minimize risk, and employing industry standard insurance vehicles and established tort liability constructs to compensate for any damage.

As a final matter, the authors question whether Category 1 and 2 aircraft cannot cause a significant injury.   Considering that operators of aircraft are strictly liable for injury or damage to people and property on the ground regardless of negligence or fault, it is suggested that Category 1 and 2 operators, similar to operators of larger aircraft, be required to certify financial sufficiency or have in place adequate insurance coverage to compensate those members of the public who are in fact injured or damaged by their operations.   It’s likely that the small size and impact of these aircraft, combined with granular route analysis and risk-minimizing flight planning, will yield highly affordable insurance premiums.

1) Washington Progress Group LLC (WPG) is a consulting firm consisting of senior aviation, policy, and legal subject matter experts with specific expertise in UAS technology and technology policy.    In addition to providing thought leadership within the UAS community, WPG is an active participant in NASA’s UTM planning activities and has under development an innovative proprietary tool improving risk analysis not only for UAS, but applicable to other aviation sectors, from general and commercial aviation to commercial space operations.    

2) 84 Fed.Reg. 3856

3) See “Common Risk Criteria Standards [321-07] for National Test Ranges:  Supplement,” pp. 5-34/38 (2007).

4) Matthews, et al., “An Achievable Path to UAS Integration in the NAS”, ; FAA Sponsored Sense and Avoid Workshop, “Sense and Avoid (SAA) for Unmanned Aircraft Systems (UAS), Second Caucus Workshop Report,” January 18, 2013

5) FAA Order 1100.161 CHG 1,

6) Even Category 1 aircraft should be able to contain identification easily discernable to law enforcement, e.g. miniscule microchipping similar to that available for pet identification might be workable.

7) William C. Wolff, Liability of Aircraft Owners and Operators for Ground Injury, 24 J. Air L. & Com. 203 (1957)