The FAA’s Aviation Rulemaking Committee has recommended that the FAA use a risk based analysis to determine what type of UAS can be flown in close proximity to persons. While that is undoubtedly the right approach, what does it really mean? What is the risk the public is being exposed to? How much risk is too much? Who, ultimately, decides where the line should be drawn? The Micro UAS ARC Report is a good starting place, but it will hardly be the last word.

In order to understand the ARC’s recommendations, some of the technical jargon needs to be cleared away and put in more human terms. The ARC Report recommends creating four categories of UAS. Category 1 UAS, which weigh under 8.8 ounces, are considered incapable of producing a serious injury and persons are free to fly them in crowded areas under Part 107. Category 2 includes any UAS that has less than a 1% chance of producing “an AIS level 3 or greater injury” if it hits someone. Category 3 and 4 are limited to UAS that, in the event it strikes a person, have a 30% or less chance of inflicting an AIS level 3 injury. So, what does that really mean in terms of the effect on a person who is struck?

The Abbreviated Injury Scale (AIS) provides a method of quantifying the severity of an injury on a scale of 1 to 6, where level 1 is considered a “minor” injury that does not require professional treatment and level 6 is a “maximum” injury which is considered untreatable and unsurvivable. See Traffic Safety and the Driver, Leonard Evans at 4-5 (1991). A level 3 injury, chosen as the benchmark by the ARC, is classified as “serious.” Id. Such injuries carry with them the “potential for major hospitalization and long-term disability but [are] not normally life-threatening.” Id.

This helps put a “class 3 injury” in context, but can it be further quantified? It turns out that the Department of Transportation has already done this work. In its 2015 memorandum entitled Guidance on Treatment of the Economic Value of a Statistical Life (VSL) in U.S. Department of Transportation Analyses, the DOT analyzed fifteen studies conducted since 1997, and concluded that the average economic impact from the loss of one human life is $9.4 million. The memorandum also broke down the values for each class of injury on the AIS, and determined that a class 3 “serious” injury has a societal economic cost of $987,000.

So, in the case of Category 3 and 4 UAS, we are talking about vehicles where there is up to a 30% chance that a collision will produce a million dollar injury. That, however, is only half of the risk equation. The unknown question is, how many collisions per 100,000 hours of flying will there be? Will it be a thousand? Ten? One?

At the end of the day, it is the public that decides how much risk is too much, and that decision is not always rational or numbers driven. In the case of automobiles, the public is willing to tolerate an enormous amount of risk; over 30,000 deaths and 2 million injuries per year. For commercial air travel, tolerance for fatal accidents by the public is virtually non-existent, with even one accident viewed as too many.

The public tolerates a high number of deaths and injuries from motor vehicles because the freedom to get in a car and go anywhere at any time is worth it to most Americans. Ultimately it is this intangible perception by the public of the benefit from the risk that will determine if the new rules for flight over persons will be a success. The public will decide how many injuries with the “potential for major hospitalization and long-term disability” it is worth each year to get exciting footage of concerts or protests or events on the evening news. If people see a real benefit, then the number will be high. If the public ultimately decides the end product is interesting, but of low value, their tolerance for injured bystanders will be low.

This is why the notice and comment period of any major rulemaking is of such value. It is the time for the public to make its voice heard, and the regulators to determine if their proposed rules can be a success in light of public concerns or opposition. While the FAA ultimately creates the rules that go into force, it is the Congress, driven by the concerns of the public, which always has the last say on how much risk is too much.