The emergence of affordable, scalable small uncrewed aircraft systems ("UAS" or "drones") has the potential to transform numerous facets of everyday life. Because they are small, nimble, relatively easy to operate, and remotely piloted, drones offer significant opportunities that crewed aviation largely has not, including the ability to access hard-to-reach places and to sustain safe flight at very low altitudes—all at much lower price points and with much lower risk than traditional crewed aircraft. Practically, the benefits are unending: quick access to lifesaving medications in rural areas; better realtime image collection for purposes such as newsgathering, search and rescue, and monitoring of natural disasters; improved infrastructure inspection capabilities that obviate the need to put people in dangerous places such as on top of cell towers or compromised structures; and sophisticated home delivery systems that decrease wait times and reduce the number of heavy vehicles on the road, just to name a few. Drones have the potential to do a significant amount of good for us, our way of life, and our future.

Congress understands the numerous societal benefits that a robust drone ecosystem will bring, and has repeatedly passed legislation to foster the burgeoning industry. These legislative enactments include a 2012 mandate to the Federal Aviation Administration ("FAA") to integrate drones into the national airspace system, as well as numerous provisions from 2012 onward giving the FAA the requisite authority and direction to enable the remote identification ("remote ID") of drones in flight, to develop an uncrewed traffic management system ("UTM") akin to air traffic control for piloted aircraft, and to establish a process for limiting drone flights over critical infrastructure facilities, among others.

The FAA, for its part, has made significant progress integrating UAS into the existing, complex regulatory framework that has given the U.S. the safest, most secure airspace in the world. The agency has adopted enabling regulations that allow for routine (but limited) UAS flights by commercial entities, expanded those regulations to permit routine operations at night and over people, and established remote ID requirements which, once fully implemented, will ensure that law enforcement and public safety around the country can identify UAS in flight and verify that they are safe actors authorized to be in the airspace. Although the pace has been measured, the FAA has a long-term regulatory vision that ends with full integration of all manner of UAS—including, ultimately, those that will carry human passengers.

Other stakeholders may not be as ready for the drone future, or, at a minimum, are raising questions as to their role in it. For instance, some property owners have asked questions like "Do I own the airspace above my property?" and "Can I shoot down a drone that flies over my house?" A number of state legislators and city councilmembers have asked whether they can or should pass laws that govern—and tax—drones operating in the airspace above their jurisdictions. And think tanks have speculated about how the drone industry could be confined to serve other interests, proffering ill-fitting solutions in search of problems such as "drone highways," or even tollways, above the surface roads.

At the heart of these inquiries are fundamental legal questions about the scope of private rights in real property, the nature of the airspace, the scope of the federal government's authority to regulate aviation—and, importantly, whether any of these long-established paradigms should be considered differently, altered, or even reimagined to accommodate an airspace that includes low-altitude, small UAS operating at scale.

This paper addresses the legal and policy issues that animate these questions, and puts forth a comprehensive vision for how airspace regulation and the exercise of property rights should work in an advanced aviation environment. At bottom, we argue that existing legal doctrines need not be changed to accommodate the arrival of the drone—and in fact, these doctrines can all work quite well together to establish a framework in which landowners have clear, understandable rights in their real property, and in which it is clear what role states and localities can play with respect to activity that occurs in the airspace above it.

We posit that there are two overarching legal questions that need to be answered to understand the path forward for airspace regulation in the era of advanced aviation: "What rights do individual property owners have in the airspace above their property?" and "What authority do states and localities have to regulate the aviation activities that occur in the airspace above their jurisdictions?" While these questions are often conflated, it is important to take them—and understand the answers—in turn.

PART I of this paper addresses the rights of individual property owners, recounting the evolving legal understanding of real property rights following the advent of powered flight in the early twentieth century. It concludes that under current law the owners of real property possess a robust right in the surface of their property, but that it is a mistake to say they have an equivalent right in the air itself.

PART II addresses the authority of states and localities, tracing the history of federal occupation of the fields of air navigation and aviation safety, and concludes that nonfederal sovereigns cannot regulate so as to infringe upon these areas.

Part II also offers the evolution of federal control over radiofrequency spectrum as a means to better understand the proper regulatory paradigm for control of the airspace. Both Part I and Part II also discuss the concept of "navigable airspace"— what it means, where it came from, and how it fits in with the legal theories of property rights (Part I) and federal preemption (Part II).

PART III addresses the implications of these foundational frameworks for drones and the low-altitude airspace that drones will occupy at scale.

Part III explains that once the primary concepts are understood— (i) real property rights as extending only to airspace activity that affects use of property on the ground, (ii) the federal government's occupation of the fields of air navigation and aviation safety, and (iii) the concept of "navigable airspace" as both distinct from the property law concept of "immediate reaches" and insignificant as a purported legal barrier to federal regulation— layering these legal lenses atop one another presents a clear picture for stakeholder rights and responsibilities with respect to a droneintegrated airspace.

PART IV addresses alternative policy suggestions that others have made, including drone highways and toll roads, and explains why these types of solutions are unnecessary as a matter of law, likely preempted in their implementation, and misguided as a matter of policy.

PART IV addresses alternative policy suggestions that others have made, including drone highways and toll roads, and explains why these types of solutions are unnecessary as a matter of law, likely preempted in their implementation, and misguided as a matter of policy.

PART V offers a roadmap—or, perhaps more fittingly, a flight plan—for how states and localities can put together legislative enactments that not only avoid unduly infringing upon federal law, but also help to promote the burgeoning UAS industry to the benefit of their constituents, all while safeguarding those constituents' concerns.

The best such efforts will be those that leverage existing law to the extent possible, draw meaningful distinctions between air-based and landbased conduct, avoid direct or inadvertent regulation of airspace or aviation safety, and maximize consistency across the state.

Ultimately, this piece seeks to demonstrate that while the advent of drones may appear to pose an inflection point for a variety of traditional legal concepts, these supposed conflicts are, in actuality, easily resolved. Moreover, this piece emphasizes that understanding the interplay between technological development and legal doctrines is critical to our continued ability to have technological development. The debates occurring in the drone world are not new; more than 100 years ago the invention of the airplane and the recognition of aviation as central to societal progress challenged notions of what real property and the airspace even are under the law. Radio technologies did the same for the airwaves. Legal debates around UAS operations in the United States are history repeating itself, and we already have the answers. Drones have simply required us to get more precise in articulating the nature of the rights, interests, and assets that we seek to protect, and how existing legal doctrines can be understood to provide that protection. We can answer all these questions in a way that ensures that the rules are clear for all stakeholders, and all interests are adequately safeguarded.

Part I: Real Property Owners Have Robust Rights in the Surface, But Not the Airspace Itself

A. Ad Coelum as a Theory of Infinite Ownership

When early U.S. courts had to determine the scope of real property ownership, well before the advent of aviation, they often drew on an "ancient principle" known as the "ad coelum" doctrine. Observed in early English common law and "famously reiterated by Blackstone" in his 18th Century treatise Commentaries on the Laws of England, the phrase ad coelum is short for "[c]ujus est solum ejus est usque ad coelum"—roughly translated, "one who owns the soil owns to the heavens above."1 This was because, Blackstone observed, "[l]and ha[s] ... in its legal signification, an indefinite extent, upwards as well as downward."2 In the early to mid-19th century, U.S. courts used the ad coelum maxim to conclude that titles to land included the structures that sat on the land,3 as well as to adjudicate trespass cases.4

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1. 29 Main St., LLC v. U.S. Postal Serv., No. 3:19-CV-2003 (SRU), 2022 WL 972412, at *14 (D. Conn. Mar. 31, 2022) (citing 42 A.L.R. 945).

2. 2 William Blackstone, Commentaries 18; see also 1 Coke on Littleton *4a; 3 James Kent, Commentaries *401.

3. See Powell v. Monson & Brimfield Mfg. Co., 19 F. Cas. 1218, 1225 (C.C.D. Mass. 1824); United States v. Harris, 26 F. Cas. 185, 187 (C.C.D. Mass. 1830).

4. See, e.g., Markham v. Brown, 37 Ga. 277, 280–81 (1867) ("Where two persons claim to have actual possession of the same land, he is deemed in possession who has the legal title, and the other is a trespasser. The owner of realty, having title downwards and upwards indefinitely, an unlawful interference with his rights, below or above the surface, alike gives him a right of action.") (emphasis omitted).

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