Aerial Trespass and the Fourth Amendment

Randall F. Khalil* May, 2023

Since 1973, courts have analyzed aerial surveillance under the Fourth Amendment by applying the test from Katz v. United States, which states that a search triggers the Fourth Amendment when a government actor violates a person’s “reasonable expectation of privacy.” The Supreme Court applied Katz to aerial surveillance three times throughout the 1980s, yet this area of the law remains unsettled and outcomes are unpredictable. In 2012, the Supreme Court recognized an alternative to the Katz test in Jones v. United States, which held that a search triggers the Fourth Amendment when a government actor physically intrudes into a constitutionally protected space with the intent to obtain information. Courts have largely avoided applying the Jones intrusion test to aerial surveillance. This Note explores the intersection of the Fourth Amendment, aerial property rights, and government use of drones. It argues that the Jones intrusion test can be a useful doctrinal tool for analyzing aerial surveillance under the Fourth Amendment. This issue will only grow in importance as law enforcement expands its use of use of drone technology.

Introduction

In May 2018, Long Lake Township in Northern Michigan hired a drone operator to conduct surveillance on Todd Maxon’s backyard on the suspicion he was in violation of the municipality’s zoning ordinance.¹ The Michigan Court of Appeals held that this drone surveillance violated the Fourth Amendment’s protection against unreasonable searches and seizures.² Maxon appears to be the first time a United States court declared an instance of aerial drone surveillance a search triggering the Fourth Amendment. The court’s analysis illustrated the reality that Fourth Amendment doctrine, as applied to aerial searches, is unsettled and unpredictable.

The dominant Fourth Amendment test from Katz v. United States states that a search triggers the Fourth Amendment when a government actor violates a person’s “reasonable expectation of privacy.”³ Between 1967 and 2012, the Katz “reasonable expectations” test was the sole Fourth Amendment test. Courts first began to apply the Fourth Amendment to aerial surveillance in the 1970s in cases involving fixed-wing aircraft and helicopters.⁴ In 2012, the Supreme Court recognized an alternative trespass-based Fourth Amendment test in United States v. Jones, which held that the Fourth Amendment is triggered when a government actor physically intrudes into a constitutionally protected space with intent to obtain information.⁵ Since 2012, no court has dispositively applied the Jones intrusion test to aerial surveillance.

Clarity remains as important as ever in this area of the law. Use of drones to conduct aerial surveillance has become cheap and easy,⁶ and law enforcement’s use of drones will continue to expand.⁷ This Note argues that the Jones trespass test can apply to aerial surveillance more workably than the existing Katz approach, and would lead to more predictable results and better secure citizens’ privacy. Part I recounts existing Fourth Amendment doctrine and historical applications of the Katz test to aerial surveillance. Part II examines the history of aerial trespass in Anglo-American law and attempts to answer the yet-unresolved question of how far landowners’ property rights extend into the air (at least for Fourth Amendment purposes). Part III explains how an aerial trespass test would work and applies it to several prominent aerial surveillance cases decided under Katz.

I. Current Fourth Amendment Doctrine

The Fourth Amendment states, “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated.”⁸ The Court has explained that the purpose of the Fourth Amendment is to protect “the privacy and security of individuals against arbitrary invasions by governmental officials.”⁹ Courts have long looked to property law for guidance in interpreting the reach of the Fourth Amendment.¹⁰ Formally, there are two distinct inquiries in a Fourth Amendment analysis: (1) whether the government has conducted a search or seizure under the Fourth Amendment; and (2) if so, whether the search or seizure was reasonable.¹¹ Courts frequently blur the line between these two inquiries.¹² This Note concerns only the first question: when the Fourth Amendment is triggered.

A. The Katz “Reasonable Expectations” Test Applied to Aerial Surveillance

To determine whether a Fourth Amendment search has occurred, the Supreme Court has historically applied the Katz “reasonable expectation of privacy” test.¹³ Under Katz, a Fourth Amendment search occurs when the government violates a subjective expectation of privacy that society recognizes as reasonable.¹⁴ In the context of aerial surveillance, the most important factor the Supreme Court considers is positive law—specifically FAA regulations—and whether the airspace from which the surveillance took place was open to the public. The second most important factor is the probability or frequency of public access. Finally, the lower courts have viewed “disruptiveness” as another important factor; sensitivity of setting and government intent have also proven lesser, but present, factors. The Supreme Court has never found aerial surveillance to be a Fourth Amendment search, but lower courts sometimes do.

1. Positive Law

Whether FAA regulations permit public access to airspace was the decisive factor in two of the three aerial surveillance cases decided by the Supreme Court and a necessary factor in the third. In Ciraolo v. California, law enforcement flew a fixed-wing aircraft 1,000 feet above a defendant’s backyard to search for marijuana plants.¹⁵ The Court held that this was not a Fourth Amendment search; the defendant’s expectation of privacy was “unreasonable” because “[a]ny member of the public flying in [the] airspace who glanced down could have seen everything that these officers observed.”¹⁶ In Dow Chemical, decided the same day as Ciraolo, the EPA hired an aerial photographer to take pictures of the Dow Chemical’s Midland, Michigan plant from various altitudes no lower than 1,200 feet as part of an emissions compliance investigation.¹⁷ The Court held that the aerial photography was not a Fourth Amendment search because the aircraft was lawfully within navigable airspace the entire time the photographs were taken.¹⁸

Lower courts also routinely find that aerial surveillance is not a Fourth Amendment search when there is lawful public access to the airspace.¹⁹ And in at least one case, lack of lawful public access led a court to conclude that the Fourth Amendment was triggered. In 2009, the Ohio Court of Appeals held in State v. Little that police helicopter surveillance conducted 100 to 600 feet above the defendants’ property triggered the Fourth Amendment because the pilot operated illegally in “closed” airspace near the Dayton International Airport.²⁰ The court concluded that the aircraft violated the defendants’ reasonable expectation of privacy “when it viewed the contraband on [their] property” within the FAA-restricted airspace.²¹

Lack of lawful public access was also relevant in People v. Sneed—the first aerial surveillance Fourth Amendment case decided in any court in the United States.²² There, the California Court of Appeal suggested that a police helicopter hovering twenty to twenty-five feet above the defendant’s backyard was “probably illegal.”²³ But this analysis was not necessary to the court’s conclusion.²⁴

2. Frequency of public access

The second most important factor in Fourth Amendment aerial surveillance case law is the probability or frequency of public access into the airspace at a given altitude. This was the decisive factor in Justice O’Connor’s concurring opinion in Florida v. Riley,²⁵ which provided the critical fifth vote concluding that a helicopter flyover was not a Fourth Amendment search. In Riley, a law enforcement helicopter hovered 400 feet over the defendant’s home for several minutes and discovered marijuana growing in a greenhouse.²⁶ A fractured Court held that this did not implicate the Fourth Amendment. Justice White’s plurality opinion reasoned that it was “of obvious importance that the helicopter . . . was not violating the law,” because FAA regulations provided that “[a]ny member of the public could legally have been flying over Riley’s property in a helicopter at the altitude of 400 feet and could have observed Riley’s greenhouse.”²⁷

But O’Connor’s concurrence argued that FAA regulations concerned safety rather than compliance with the Fourth Amendment, and that the test for determining if the defendant had a reasonable expectation of privacy should instead be “whether the helicopter was in the public airways at an altitude at which members of the public travel with sufficient regularity.”²⁸ O’Connor concluded without evidence that such overflights were sufficiently common and, therefore, Riley’s expectation of privacy was unreasonable.²⁹ Lower courts often similarly assume, without justification, that frequent public access defeats a reasonable expectation of privacy,³⁰ but sometimes they require proof that overflights were, in fact, common to show the expectation of privacy was not reasonable at all.³¹

3. Disruptiveness

In the small subset of aerial surveillance cases in lower courts that concluded the Fourth Amendment was triggered, disruptiveness was often the critical factor. Justice White’s plurality opinion in Florida v. Riley suggested that it was relevant that the helicopter did not “interfere[] with respondent’s normal use of the greenhouse or of other parts of the curtilage” and that there was “no undue noise, and no wind, dust, or threat of injury.”³² Lower courts subsequently latched onto this dictum.

In 1990, the Pennsylvania Supreme Court held in Commonwealth v. Oglialoro that aerial surveillance of a barn triggered the Fourth Amendment when a helicopter hovered fifty feet above the barn for fifteen seconds and passed over the barn at least three times over five minutes.³³ It was critical to the court that the helicopter flight posed a risk of harm to the resident and her property, and that the resident was “present in the home at the time” and “experienced . . . loud noise, and vibration of the house and windows.”³⁴ Similarly, the Colorado Court of Appeals held in People v. Pollock that helicopter aerial surveillance constituted a Fourth Amendment search when a helicopter “descended to 200 feet, . . . hovered in the area [of the defendant’s property] for several minutes,” and created “enough noise that numerous people ran out” to see what was happening.³⁵

Another example in which a court found disruptiveness to be the decisive factor comes from New Mexico. In 2015, the New Mexico Supreme Court held in State v. Davis that a helicopter search at an altitude of fifty feet triggered the Fourth Amendment because a helicopter flight at such a low altitude possessed a great “degree of intrusiveness” and posed a “risk of actual physical intrusion.”³⁶ The court found it relevant that the helicopter caused minor property damage, generated excessive noise, and kicked up dust and debris.³⁷

4. Sensitivity of Information

Courts sometimes consider the sensitivity of the information likely to be obtained when assessing whether the Fourth Amendment is triggered in aerial surveillance. But this factor is rarely, if ever, dispositive. In Dow Chemical, the court indicated that the industrial nature of the chemical plant surveilled brought the case into the “open fields doctrine” and suggested that the chemical plant was less protected than the private home surveilled in Ciraolo.³⁸ The open fields doctrine states that open fields are not protected by Fourth Amendment;³⁹ its rationale is that open fields “do not provide the setting for those intimate activities that the Amendment is intended to shelter.”⁴⁰ But this distinction seems irrelevant since, in both Dow Chemical and Ciraolo, it was dispositive that surveillance took place from navigable airspace open to the public.⁴¹

5. Intent to Surveil

In Sneed,⁴² the California Court of Appeal concluded that the helicopter search triggered the Fourth Amendment and found it critical that the police officers had a subjective intent to surveil the defendant.⁴³ No other aerial surveillance case has discussed intent to surveil, possibly because such intent is obvious in context. And Fourth Amendment doctrine has since evolved such that a police officer’s subjective intent to surveil alone is not sufficient to implicate the Fourth Amendment.⁴⁴

B. The Jones Intrusion Test

In 2012, the Supreme Court articulated an alternative to the Katz test in United States v. Jones.⁴⁵ In Jones, the Court held that a Fourth Amendment search occurs whenever a government actor physically intrudes into a constitutionally protected space with an intent to obtain information.⁴⁶ The Court found that the warrantless installation of a GPS tracker onto a car, and use of that tracker to monitor the car’s location, triggered the Fourth Amendment.⁴⁷ The Court has subsequently applied Jones’s trespass test in only one subsequent case, Florida v. Jardines, which held that police officers bringing a drug-sniffing dog onto the front porch of a home was a search triggering the Fourth Amendment.⁴⁸ While Jones represented a departure from the Court’s exclusive reliance on Katz, it was consistent with a line of cases before Katz in which a Fourth Amendment search required “intrusion into a constitutionally protected area.”⁴⁹

Both Jones and Jardines rely on analogy to property torts to determine the reach of the Fourth Amendment. Jones analogized to the tort of trespass to chattels to determine whether a physical intrusion had taken place.⁵⁰ Jardines analogized to implied licenses and custom to determine whether the homeowner had implicitly consented to members of the public marching their drug-sniffing dogs onto the defendant’s front porch to search for drugs.⁵¹

This Note will argue that the Jones test should form the backbone of any Fourth Amendment aerial trespass test. However, I have found no cases in which a court has relied on Jones (or Jardines) in analyzing aerial surveillance under the Fourth Amendment.⁵² The key questions that must be resolved before applying the Jones test to aerial surveillance are: (1) What counts as trespass in air and (2) Which air is “constitutionally protected?” Part II addresses these questions.

C. Long Lake Township v. Maxon

In Long Lake Township v. Maxon, the Michigan Court of Appeals, applying Katz, held that flying a drone over the defendants’ property at a height lower than 400 feet triggered the Fourth Amendment.⁵³ A northern Michigan municipality investigated a junk and salvage operation on the defendants’ property for alleged violations of the township’s residential zoning restrictions and hired a drone operator to photograph the defendants’ property.⁵⁴ The Michigan Court of Appeals held that the drone surveillance was a Fourth Amendment search and suppressed the drone’s photographic evidence from use in a civil enforcement action.⁵⁵ Applying Katz, the court held that the defendants had a “reasonable expectation of privacy in their property against drone surveillance.”⁵⁶ Distinguishing the Supreme Court’s aerial surveillance cases that found no Fourth Amendment search, the court here noted that “drones are qualitatively different from airplanes and helicopters: they are vastly smaller” and fly at lower altitudes.⁵⁷

Although the court grounded its conclusion in Katz, its reasoning blurred the line between “reasonable expectation of privacy” and physical intrusion.⁵⁸ The court said that because drones fly “below what is usually considered public or navigable airspace,” “flying them at legal altitudes over another person’s property without permission or a warrant would reasonably be expected to constitute a trespass.”⁵⁹ But the court did not decide whether the drone committed a trespass, saying “there is little meaningful distinction” between whether the drone was located just inside or just outside the property line.⁶⁰

II. Defining Aerial Trespass

Adopting a trespass-based Fourth Amendment test for aerial surveillance requires answering the yet-unresolved questions of who owns the air and which airspace is in the public domain. United States citizens accept that airplanes may fly over our properties, perhaps because we benefit from them, or perhaps because they typically cause us no harm.⁶¹ The Court has applied the Jones test only to intrusions upon concrete physical spaces,⁶² but an intrusion by a drone into the airspace above a home is different. The extent to which landowners’ property rights extend into the air is doctrinally unclear, as is the formal nature of the public’s right to access navigable airspaces (i.e., whether the United States has title to navigable airspace or a public easement through privately owned airspace).

Section II.A recounts the history of the ad coelum principle, which reflects the common law concept that a surface owner’s property rights extend infinitely upward into the heavens. Section II.B describes how the ad coelum principle evolved during the aviation era. And Section II.C explains Congress’s assertion of national sovereignty in the air and its designation of publicly accessible “navigable airspace.”

A. The Ad Coelum Principle

One of the earliest known English cases governing ownership of airspace is from 1598 and involved a landlord suing his neighbor for building a house that hung over his property line.⁶³ The defendant did not trespass onto the plaintiff’s ground but was found liable nonetheless.⁶⁴ This aerial trespass principle was included in Chief Justice Edward Coke’s Institutes of the Laws of England, in which he explained that land was not just two-dimensional, but encompassed “[air] and all other things even up to heaven; for cujus est solum ejus est usque ad coelum.”⁶⁵ The ad coelum principle in English common law has roots in the Roman Law revival of the twelfth and thirteenth centuries,⁶⁶ and may have been a historical accident caused by misinterpretation of Roman civil law.⁶⁷

Regardless, American law incorporated the ad coelum rule. A few nineteenth-century cases, citing the ad coelum principle, considered whether overhanging tree branches were aerial trespasses.⁶⁸ In 1906, New York’s highest court held that a telephone wire strung thirty feet over a plaintiff’s house was a trespass, reasoning that the “plaintiff as the owner of the soil owned upward to an indefinite extent . . . [including] the space occupied by the wire, and had the right to the exclusive possession of that space.”⁶⁹ Courts also applied the principle to moving objects. In 1925, the Supreme Court of Montana held that a bullet fired from a shotgun that traveled above the plaintiff’s land was “a technical trespass at least.”⁷⁰ And in a 1922 takings case, the Supreme Court characterized multiple gun shots fired from a military base across the plaintiff’s coastal resort as a trespass.⁷¹

B. Erosion of the Ad Coelum Principle in the Aviation Era

In 1903, the Wright brothers took their first flight. In the following decades, courts began to signal that the ad coelum rule should not be understood to mean that property ownership literally extended infinitely upward.⁷² Congress regulated aviation for the first time with the Air Commerce Act of 1926,⁷³ which declared that the United States “has, to the exclusion of all foreign nations, complete sovereignty of the airspace over the lands and waters of the United States.”⁷⁴ The Act defined “navigable airspace” as “airspace above the minimum safe altitudes of flight prescribed by the Secretary of Commerce,” and provided that “such navigable airspace shall be subject to a public right of freedom of . . . air navigation.”⁷⁵ The corresponding House Report explained that “[t]he public right of flight in the navigable air space” is comparable to the “public easement of navigation in the navigable waters.”⁷⁶

In 1936, the Ninth Circuit held in Hinman v. Pacific Air Lines Transport that the ad coelum principle was not to be taken literally.⁷⁷ Landowners near an airport brought a trespass action against several airlines and sued to enjoin them from flying over their land.⁷⁸ The court denied the injunction, and explained that ad coelum was an antiquated principle that simply intended “that the owner of the land could use the overlying space to such an extent as he was able.”⁷⁹

The Ninth Circuit explained that ad coelum was inconsistent with two key attributes of property: (1) the exercise of dominion, and (2) the capacity for exclusive possession.⁸⁰ Landowners cannot exercise dominion in the upper reaches of the air, and such air lacks the capacity to be exclusively possessed. Established case law at the start of the twentieth century applied the ad coelum principle only to intrusions that were relatively close to the surface of the Earth—a telephone wire thirty feet high, a tree branch, a bullet shot from a gun at ground level, or a structure protruding from a neighboring building. The principle had never applied to objects flying thousands of feet high.

The Supreme Court denied certiorari to review Hinman,⁸¹ but in 1945, the Court adopted its key holding in United States v. Causby.⁸² A farmer close to a military airport in North Carolina sued the U.S. government for flying aircraft across his land at altitudes as low as eighty-three feet, which harmed his chicken-farming operations.⁸³ The Court reiterated that ad coelum does not apply literally,⁸⁴ but held that a landowner has “exclusive control of the immediate reaches of the enveloping atmosphere . . . [and] owns at least as much of the space above the ground as he can occupy or use in connection with the land.”⁸⁵

The Court also concluded that a taking had occurred.⁸⁶ Invoking the Air Commerce Act of 1926, the Court reasoned that “[t]he navigable airspace which Congress has placed in the public domain is ‘airspace above the minimum safe altitudes of flight prescribed’” by regulation.⁸⁷ The Court concluded that the flights in question, at an altitude of eighty-three feet, were well below the minimum allowed (which began at 300 feet). Thus, they were not within navigable airspace, which Congress had placed in the public domain.⁸⁸ Causby remains the basis of aerial takings claims today.⁸⁹

C. Aerial Trespass Today

So, what do Causby, Hinman, and the statutory scheme enacted by Congress tell us about how far property ownership extends into airspace? First, ad coelum does not apply literally, and federal law sets a clear upper bound on a landowner’s property interest in airspace. Second, there is some minimal amount of airspace above land where trespass is actionable, but only if the trespass (i) occurs within the “immediate reaches”⁹⁰ of the land and (ii) results in “interference with actual . . . use”⁹¹ of the property. Property interests are most uncertain in the zone in between the “immediate reaches” and the boundary where navigable airspace begins.⁹² Lastly, state law plays a limited role in defining the scope of aerial property rights.⁹³

1. Clear Inferences

First, and most importantly, aerial trespass today has a clear upper bound. Property rights in land do not extend infinitely ad coelum. Congress first regulated aviation in 1926 and defined navigable airspace as the zone above a minimum safe altitude to be set by an agency. Property ownership of airspace thus extends at most to the point above which Congress permits all aircraft to access.⁹⁴ The FAA minimum safe altitudes in effect since 2010⁹⁵ are codified at 14 C.F.R. § 91.119:

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:

. . . .

(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.

(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

(d) Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface—

(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and

(2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section. ⁹⁶

This rule indicates that the highest minimum point at which navigable airspace begins is 1,000 feet above the highest obstacle within a radius of 2,000 feet in a “congested area.” The tallest building in the country currently is One World Trade Center in Manhattan standing at 1,776 feet.⁹⁷ So, the highest navigable airspace boundary anywhere in the country is at 2,776 feet within the 2,000-foot radius around One World Trade Center. In most parts of the country, located in “other than congested areas,” the upper bound is 500 feet.⁹⁸

Courts largely followed Causby’s theory of a “fixed height” limit.⁹⁹ The rule promoted some degree of certainty and discouraged litigation by making clear that no trespass claim is actionable in airspace above the altitude where navigable airspace begins.¹⁰⁰ Determining whether an area is “congested,” “other than congested,” or “sparsely populated” can be a tricky, fact-specific inquiry, but FAA adjudications, FAA guidance documents, and case law provide clarity.¹⁰¹

Second, Causby clarifies that there is some amount of airspace—the “immediate reaches”—in which trespass is actionable.¹⁰² The “immediate reaches” rule is not binding on states, but it is persuasive authority, and it is reflected in the Restatement of Torts.¹⁰³ Some states permit aerial trespass actions beyond the “immediate reaches”¹⁰⁴ (although Section 91.119 would preempt contrary state law allowing trespass actions above the “navigable airspace” line¹⁰⁵).

Third, Causby suggests that there must be “interference with actual use” for aerial trespass to be actionable.¹⁰⁶ The “interference with actual use” requirement is similarly not binding on states, although many states have adopted it.¹⁰⁷ It is also not clear that it is an independent element, as opposed to a factor intertwined with the “immediate reaches.” For example, the Restatement of Torts explains that the extent of the “immediate reaches” is defined, at least in part, by whether the trespass results in “interference with actual use.”¹⁰⁸ Claimants often satisfy the requirement by showing that the aerial trespass caused excessive noise.¹⁰⁹

2. The Ambiguous Middle Area

There is a subsection of airspace above land, the “immediate reaches,” in which aerial trespass is actionable, though the boundary of this zone is not precisely defined. It is also clear that surface owners have no property interest in the navigable airspaces which Congress has placed in the public domain, usually airspace above 500 feet where all aircraft have a right of access. What about the zone in between? No one seems to know.¹¹⁰

Some dicta in Causby seem to suggest that everything beyond the “immediate reaches” is in the public domain,¹¹¹ and thus, there is no ambiguous middle zone. But this may just be dicta concerning how North Carolina state law would apply; otherwise it would contradict other parts of the opinion which make clear that only the airspace above the FAA-prescribed minimum safe altitudes is in the public domain.¹¹² In fact, on remand, the lower court in Causby suggested that a surface owner maintains a property interest in all airspace below the minimum levels set by regulation.¹¹³

Between Causby and the federal aviation statutes and regulations in effect today, it may appear as though there is no bright line demarcating navigable airspace in the public domain.¹¹⁴ The location of the boundary seems to vary depending on at least (1) the type of aircraft flown (e.g., whether it’s a helicopter or a fixed-wing aircraft),¹¹⁵ (2) whether the aircraft is taking off or landing versus in mid-flight,¹¹⁶ (3) the height of the tallest “obstacle” within 2,000 feet,¹¹⁷ and (4) in “sparsely populated areas,” the presence of a “person, vessel, vehicle, or structure.”¹¹⁸ For example, a homeowner could extend the navigable airspace boundary above her land by building an “obstacle” like a tall tower on her land.¹¹⁹ In the past, there were even more relevant factors.¹²⁰ And of course, the entire regulatory scheme is subject to new rules that the FAA may promulgate.

These complications notwithstanding, in the typical “other than congested” area where the FAA prescribed minimum safe altitude is 500 feet: (a) trespass above 500 feet in altitude is never actionable; and (b) trespass within 50 feet is almost certainly actionable (as it almost certainly causes “interference with actual use”). In airspace between 50 and 500 feet, whether trespass is actionable depends on a fact-specific inquiry about whether the trespass was within the “immediate reaches” (whatever this may mean), and/or whether it “interfere[d] with actual use.”¹²¹

3. Limited Role for State Law

The federal law ensures a limited role for state law concerning aircraft access to airspace. The FAA interprets the federal aviation regulations as preempting state law from regulating aviation safety or navigable airspace.¹²² The principles of conflict preemption apply whenever states and local governments attempt to enact regulations in parallel with FAA regulations.¹²³ But state law does matter to some extent because it provides the cause of action for trespass actions.¹²⁴ After all, property law is traditionally a creature of state law.¹²⁵ And there are some differences between states’ definitions of the tort of trespass.¹²⁶

But the Court has said that the specific laws of individual states should not govern the reach of the Fourth Amendment, because then there would be a different Fourth Amendment in each state.¹²⁷ So while state property law principles may inform courts’ understanding of the reach of the Fourth Amendment, differences in property law between individual states are not significant.

III. Aerial Trespass and the Fourth Amendment

This Note argues that aerial property rights can be analyzed with a two-tiered approach: (1) the “lower zone” below an area’s prescribed minimum safe altitude, and (2) the “upper zone” above the applicable minimum safe altitude. Aerial trespass may be actionable in the “lower zone,” but is never actionable in the “upper zone.” Section III.A proposes an aerial trespass test: a Fourth Amendment search never occurs in the “upper zone,” but presumptively occurs when a state actor intrudes into the “lower zone” with the intent of obtaining information. Section III.B applies the test to several prominent aerial surveillance cases and highlights where this test would lead to different outcomes. Section III.C addresses counterarguments to the aerial trespass test. And Section III.D explains the advantages of the aerial trespass test against the current Katz approach.

A. The Fourth Amendment Aerial Trespass Test

1. Proposal

Reconciling the aerial property rights from Causby and Hinman with Jones’s Fourth Amendment physical intrusion test, this Note proposes the following trespass-based Fourth Amendment test for aerial surveillance:

Lower zone: A Fourth Amendment search presumptively occurs when a state actor intrudes into the airspace above a home or other constitutionally protected real property below the unambiguous public domain with the intent of obtaining information. The state may rebut this presumption by showing that the frequency of aerial intrusions of the same nature was so great as to amount to an implied easement or taking.
Upper zone: The Fourth Amendment is not implicated when a state actor is lawfully within the unambiguous public domain. The unambiguous public domain is defined as navigable airspace above the minimum safe altitudes defined by FAA regulations in which all aircraft may be lawfully present.

No Fourth Amendment claim would be cognizable in the “upper zone.”¹²⁸ In most areas classified as “other than congested,” this zone begins at 500 feet.¹²⁹ In “sparsely populated” areas, there is no minimum, but aircraft must avoid coming within 500 feet of any person, vessel, vehicle, or structure.¹³⁰ In “congested areas,” the unambiguous public domain begins at 1,000 feet above the highest obstacle within a radius of 2,000 feet¹³¹—beginning, for example, at 2,776 feet around the World Trade Center in Manhattan.

The contours are less clear in the lower zone. There is near-consensus that aerial trespass is actionable within the “immediate reaches,” which consists of “as much space above the ground as [a landowner] can occupy or use in connection with the land.”¹³² In Causby, the airplanes flying at eighty-three feet above the plaintiffs’ land regularly came within sixty-seven feet of the house, sixty-three feet of the barn, and eighteen feet of the highest tree, and this was held to be within the “immediate reaches.”¹³³ A trespass fifty-feet high “which interferes with actual use” would likely be included, while a trespass within 150 feet “may present a question of fact” as to whether it is also included.¹³⁴

What about the space above the “immediate reaches” but below the unambiguous public domain? This would include, for example, a fixed-wing aircraft flying at a height between 200 and 500 feet in an “other than congested” area, a helicopter flying at 800 feet in a congested area, or a fixed-wing aircraft flying at 300 feet over a lone structure in a “sparsely populated” area.¹³⁵ This “middle space” may not exist in some areas, such as sparsely-populated areas, where no FAA minimum safe altitude applies.¹³⁶ But where it does exist, the scope of landowners’ property rights is the most uncertain.¹³⁷ This Note avoids such ambiguity by proposing that a Fourth Amendment search would presumptively occur in the entirety of the “lower zone.” But out of an abundance of caution, and to safeguard the workability of an aerial trespass test, this proposal would allow the state to rebut the presumption upon showing that the federal government has placed the airspace in the public domain,¹³⁸ or that aerial intrusions occur frequently enough to give rise to an implied easement or a taking.¹³⁹ A court is more likely to find an implied easement at higher altitudes.

2. Evoking Sabo

This Note is not the first proposal of a two-tiered approach to analyzing aerial surveillance based on FAA-prescribed minimum safe altitudes. In People v. Sabo, a San Diego County Sheriff’s Department helicopter circled several times above a greenhouse in a defendant’s backyard at an elevation of 400 to 500 feet and identified marijuana plants within the greenhouse.¹⁴⁰ The California Court of Appeal held that the helicopter surveillance was a Fourth Amendment search.¹⁴¹ The court distinguished Ciraolo and Dow Chemical, explaining that unlike the helicopter in Sabo, the aerial surveillance in both of those cases took place within navigable airspace.¹⁴² The court observed that its approach created “a two-tiered concept”: within navigable airspace, the Fourth Amendment is categorically not implicated per Ciraolo and Dow Chemical; but below navigable airspace, a court must conduct a “traditional inquiry into reasonable privacy expectation.”¹⁴³

The Florida Supreme Court relied on Sabo to reach its decision in Riley.¹⁴⁴ But in a fractured opinion, the United States Supreme Court reversed the Florida Supreme Court.¹⁴⁵ Given this fracture, it is unclear whether any aspect of the Sabo approach remains good law today.

But there is one key difference between Sabo and this Note’s proposal: Sabo was grounded in the language of Katz. Specifically, Sabo explained that, while aerial surveillance in navigable airspace does not implicate the Fourth Amendment because observations made from navigable airspace are in “plain view,” aerial surveillance below navigable airspace “continues to call for traditional inquiry into reasonable privacy expectation.”¹⁴⁶ By contrast, this Note presumes that aerial surveillance conducted at altitudes below navigable airspace constitutes a Fourth Amendment search. Unlike in Sabo, factors such as intrusiveness, excessive sound, hazard to people or property, and a helicopter’s ability to perform “aerial acrobatics” are irrelevant.¹⁴⁷

3. “Interference with Actual Use?”

For aerial trespass to be actionable in tort, a plaintiff must generally show that the trespass “interfere[d] with actual use.”¹⁴⁸ The most recent Supreme Court case alluding to the “interference with actual use” requirement—Florida v. Riley—suggested that “interfere[nce] with respondent’s normal use” of their property would be necessary for aerial trespass to implicate the Fourth Amendment.¹⁴⁹ This suggestion, however, was dictum in a plurality opinion.

Moreover, Fourth Amendment law is not strictly tied to trespass. Even in Jones, analogy to trespass served as a proxy for ascertaining when the Fourth Amendment was triggered. While a suit for trespass to chattels requires “some actual damage to the chattel,”¹⁵⁰ Jones held that affixing a GPS tracker onto the defendant’s car was enough to constitute a Fourth Amendment search, even though the tracker caused no damage to the car and the defendant was not aware that the tracker was installed.¹⁵¹

In tort law, an “interference with actual use” requirement in an aerial trespass claim (or “actual damage” in a trespass-to-chattels claim) makes sense. It reflects the policy judgment that only cases in which damages are quantifiable are important enough to merit the attention of courts.¹⁵² The logic of this requirement in Causby is similar.¹⁵³ For purposes of the Fourth Amendment, this rationale is inapposite. The harm caused by a Fourth Amendment violation is significant even when actual damages cannot be quantified. The harm inflicted is the state actor’s intentional invasion of a person’s privacy, not the incidental property damage that a search may cause.

The “interference with actual use” requirement has become an important factor in lower courts, and there are many cases where such a requirement is met,¹⁵⁴ but the requirement would severely limit the applicability of the Fourth Amendment to searches conducted by minimally invasive, small, unmanned aircraft as in Maxon. When a state actor commits an aerial trespass with the intent to obtain information from within the trespassed space, that interference should be enough.¹⁵⁵

B. The Aerial Trespass Test Applied

Many, if not most, cases would come out the same way under this Note’s aerial trespass test as under Ciraolo and Dow Chemical. But in the trickiest borderline cases, the aerial trespass test will promote regularity in the law and eliminate the problem of arbitrary and unpredictable outcomes. This Section applies the aerial trespass test to the Supreme Court’s aerial surveillance cases and to Maxon.

1. Ciraolo and Dow Chemical

Ciraolo would come out the same way under the aerial trespass test. In Ciraolo, law enforcement used a fixed-wing aircraft to fly over the defendant’s house at an altitude of 1,000 feet (within navigable airspace) to surveil his backyard.¹⁵⁶ Therefore, Ciraolo would be an easy case involving surveillance from the unambiguous public domain. The aircraft was within navigable airspace at a level that would have been accessible to all aircraft, so no Fourth Amendment search occurred. Dow Chemical would come out the same way too. Recall that in Dow Chemical, the EPA used an airplane to photograph an industrial plant from well within navigable airspace.¹⁵⁷ No Fourth Amendment search occurred.

2. Riley

Florida v. Riley is a more challenging case. Under the aerial trespass test, a Fourth Amendment search occurred. In Riley, police conducted helicopter surveillance of the defendant’s backyard from a height of 400 feet.¹⁵⁸ At 400 feet, the helicopter might not have committed an actionable trespass in tort (since aerial trespass is generally actionable only in the “immediate reaches,” which generally goes no higher than 100 to 150 feet). And the helicopter might have been lawfully operating at 400 feet under an FAA rule exempting helicopters from minimum safe altitude requirements.¹⁵⁹ But the helicopter was nonetheless below navigable airspace and, therefore, in the lower zone.¹⁶⁰

This creates a tricky issue. If we accept (a) that Congress has allowed the FAA’s minimum safe altitudes to define navigable airspace, which Congress then puts in the public domain, and (b) that property interests in air extend up only to the point at which the public domain begins, then what do we do when the FAA prescribes minimum safe altitudes on a technology-by-technology basis? Section 91.119(d)(1) exempts helicopters and some other types of aircraft from minimum safe altitudes.¹⁶¹ One might argue that this regulation effectively prescribes a minimum safe altitude of zero feet for helicopters and, per Causby, that the helicopter flying at any altitude would be in the unambiguous public domain.

But as this Note has shown, Section 91.119 is best understood as setting clear lines defining the public domain as the minimum safe altitudes above which all aircraft are allowed.¹⁶² The special permission granted to helicopters and other aircraft to fly lower is best understood as a special-use easement.¹⁶³ The Court has often described regulations which limit a property owner’s right to exclude as imposing a “servitude” or an “easement.”¹⁶⁴ “An easement creates a nonpossessory right to enter and use land in the possession of another” for specified purposes or uses “and obligates the possessor not to interfere with the uses authorized by the easement.”¹⁶⁵ In Causby itself, the Court held that the frequent overflights over the Causby farm at low altitudes indicated that “a servitude has been imposed upon the land,”¹⁶⁶ and remanded to the lower court to define the scope of the easement.¹⁶⁷ Further, accepting a theory that certain segments of navigable airspace are in the public domain only for certain types of aircraft conflicts with Congress’s intent that “the public right of flight in the navigable air space” be comparable to the “public easement of navigation in the navigable waters,”¹⁶⁸ which does not vary by the type of watercraft used.

And if the helicopter exception is a public special-use easement, the helicopter in Riley exceeded any reasonable scope of that easement. Under traditional property principles, a court may enjoin the misuse of an easement without the servient owner showing damage.¹⁶⁹ Any public easement created in Section 91.119(d) would be for the purpose of navigation.¹⁷⁰ The helicopter in Riley went beyond simply cutting across defendant’s airspace; it hovered for an extended period at a low altitude to spy on the defendant’s backyard.¹⁷¹

3. Maxon

Finally, a court applying the aerial surveillance test in Maxon would conclude that a Fourth Amendment search had occurred. The record did not indicate the exact altitude at which the drone photos were taken, but the drone operator stated in an affidavit that he “maintained an altitude of less than 400 feet.”¹⁷² Additionally, the record indicates that defendant Maxon was in his backyard when he heard a drone “flying directly over his head.”¹⁷³ Given that there were people and structures around, the area was not “sparsely populated” but at least “other than congested,” so navigable airspace in the area began at no less than 500 feet.¹⁷⁴ This is enough for a court to conclude that the drone was always below navigable airspace, and that the drone did in fact cross the line into the airspace above Maxon’s property.

C. Addressing Counterarguments

The Maxon majority lodged an important critique of applying the Jones trespass test to aerial surveillance: “[W]e think there is little meaningful distinction for present purposes between ‘just inside . . .’ and ‘just outside the property line.’”¹⁷⁵ While this critique illustrates how the rigid formality of Jones might limit its usefulness, it should not detract from its utility in those cases in which it works well. Also, the aerial trespass test may help to better inform reasonable expectations of privacy in aerial surveillance even under an application of Katz. It may contribute to establishing the norm that aerial surveillance conducted at altitudes below FAA-specified minimum safe altitudes constitutes a Fourth Amendment search, even when no technical aerial trespass has occurred, by legitimating a reasonable expectation of privacy in airspace below the public domain line.¹⁷⁶

Some scholars also object to the use of FAA regulations to define the reach of the Fourth Amendment. For example, Professor Orin Kerr has argued,

Consider the FAA regulations analyzed in Florida v. Riley, the helicopter flyover case. The FAA presumably drafted those regulations to minimize noise and deter accidents, not to limit the police. Whether the police happened to fly over or under FAA airspace limits has no significant connection to whether particular police flyovers are reasonable only if justified by a warrant.¹⁷⁷

Kerr’s presumption that the FAA drafted the regulations in Section 91.119 to “minimize noise and deter accidents” is not entirely correct. As this Note has explained, Congress intended the FAA to prescribe minimum safe altitudes, at least in part, to define the scope of property rights in air.¹⁷⁸ FAA-prescribed minimum safe altitudes define “navigable airspace” in the public domain and set the boundaries at which surface owners’ property interests in airspace end.¹⁷⁹ The Supreme Court has confirmed this interpretation.¹⁸⁰ And, as this Note has explained, there is nothing unusual about looking to property interests to define the reach of the Fourth Amendment.¹⁸¹

Another drawback of the aerial trespass test is that courts will need to apply the FAA regulations in Section 91.119 to determine the minimum safe altitude in a given area. The regulations provide a loose set of standards; it may be difficult to determine whether a given area is, for example, an “other than congested area[]”¹⁸² or a “congested area.”¹⁸³ In fact, Section 91.119(b) circularly uses the phrase “congested area” to define “congested area.”¹⁸⁴ But this difficulty is not insurmountable. In many cases, a Section 91.119 zone determination will not be required at all because the surveillance will be below navigable airspace regardless of the zone.¹⁸⁵ And even when a Section 91.119 zone adjudication is required, existing case law shows that such adjudications are well within judicial competence.¹⁸⁶ Cases such as Claassen v. City & County of Denver¹⁸⁷ and Mickalich v. United States¹⁸⁸ show that courts can do this with the ordinary tools of statutory interpretation.

As a final note, there are forms of aerial surveillance which would not result in a Fourth Amendment search under the aerial trespass test but should nonetheless implicate the Fourth Amendment. For example, the ARGUS imaging system, developed by the Department of Defense, is deployed at an altitude above 17,000 feet and uses a high-powered sensor to generate a detailed, interactive map of the ground below in real time.¹⁸⁹ It can provide a persistent video feed twenty-four hours a day, seven days a week.¹⁹⁰ At 17,000 feet, there is no question that this technology would be comfortably within navigable airspace and would not implicate the aerial trespass test. But use of this technology might still implicate the Fourth Amendment under a Katz-based theory, such as the Kyllo standard¹⁹¹ or the mosaic theory of the Fourth Amendment.¹⁹² The aerial trespass test is also inapplicable to aerial surveillance at any altitude over public property, like streets and sidewalks, but such surveillance may also be covered by the mosaic theory of the Fourth Amendment.¹⁹³

D. Advantages of the Aerial Trespass Approach

Some scholars and judges have noted that the reemergence of the Jones trespass-based test has done little to change Fourth Amendment law under Katz. Justice Kagan argued in her concurring opinion in Florida v. Jardines that the Court could have arrived at the same conclusion under an application of Katz, even though she joined the Court’s opinion applying a trespass-based analysis in full.¹⁹⁴ And Justice Alito’s concurring opinion in United States v. Jones argued that the Court would have been able to reach the same conclusion—that a Fourth Amendment search had occurred—under an application of Katz.¹⁹⁵ Professors Matthew Tokson and Ari Ezra Waldman argue that the reemergence of the Jones trespass test has “[i]n practice . . . added little to the Katz test,” noting that “the Supreme Court cases in which it has been employed may have reached the same outcome under Katz.”¹⁹⁶ This conclusion is premature; the Court has applied the trespass test only twice since resurrecting it in 2012, and never in an aerial surveillance case.

This Note does not advocate for a Jones aerial trespass test to supplant Katz in all aerial surveillance cases. As explained in the previous Section, it may not be desirable in many cases to analyze aerial surveillance under the trespass-based test proposed in this Note. But a Jones trespass analysis can lead to a doctrinally straightforward answer without the ambiguities of the Katz test.

As lower court decisions show, applying the Katz test to aerial surveillance involves inconsistent factors and has led to unpredictable and sometimes conflicting results.¹⁹⁷ In the few lower court cases concluding that an aerial surveillance constituted a Fourth Amendment search, courts applied different factors in different ways. Only Sneed discussed the lawfulness of an aircraft’s presence in the air, but lawfulness was not critical there.¹⁹⁸ Frequency of flight at a given altitude over a target’s property was discussed only in Pollock.¹⁹⁹ The disruption or physical damage caused by the surveillance was a critical factor in Oglialoro,²⁰⁰ Pollock,²⁰¹ and Davis.²⁰² Conversely, intent to surveil was a critical factor in Sneed,²⁰³ but played no role in Oglialoro, Pollock, or Davis.

Yet in most aerial surveillance cases, courts applying Katz have concluded that the aerial surveillance in question does not implicate the Fourth Amendment.²⁰⁴ In Giancola, one such typical case, the court held that helicopter surveillance conducted at 100 feet above plaintiffs’ property was not a Fourth Amendment search because it comported with FAA regulations.²⁰⁵ This case is one of many examples in direct conflict with the outcomes and reasoning in Sneed, Oglialoro, Pollock, and Davis. An aerial trespass approach would provide a straightforward set of rules that can readily and easily be applied in any aerial flyover case.

Additionally, the aerial trespass test relieves courts of the need to speculate about society’s expectations of privacy. Courts applying Katz must do so regarding aerial surveillance and often in an undisciplined manner. This often occurs in aerial surveillance cases when courts make findings of fact about the “frequency” of flights at a given altitude. In Riley, Justice O’Connor’s concurrence asserted, with no evidence, that helicopter traffic 400 feet above Riley’s home was sufficiently common, and placed the burden on the target of the aerial surveillance to rebut a presumption that air traffic at a given altitude was sufficiently common if permitted by FAA regulations.²⁰⁶ In Pollock, the Colorado Court of Appeals similarly placed the burden on the target of the aerial surveillance to rebut the presumption that the Fourth Amendment was not triggered, but concluded that the defendant provided “ample” evidence to rebut the presumption.²⁰⁷ In Breza, the court concluded that the government had “established” that air traffic was sufficiently common—even though that evidence was in the form of law enforcement officers’ conclusory testimony that helicopter flights at an altitude of 100 feet over defendant’s property “were a regular occurrence.”²⁰⁸ The trespass-based approach to aerial surveillance that I propose would involve straightforward legal analysis and lead to more predictable outcomes.

Conclusion

The Jones trespass test can serve as a useful doctrinal tool for Fourth Amendment analysis of aerial surveillance.²⁰⁹ The benefits of Jones are its straightforwardness and simplicity.²¹⁰ While the big obstacle standing in the way of applying Jones to aerial trespass has been the uncertainty surrounding the nature of property rights in the air, this Note attempts to provide a framework for making sense of this uncertainty. By contrast, application of Katz to new technologies is complex and leads to unpredictable outcomes.²¹¹ While the Maxon majority had to make speculative assertions about society’s expectations of privacy with regard to drone surveillance to reach their conclusion under Katz, the Jones trespass analysis this Note proposes would lead to the same outcome through more straightforward legal analysis.

As Justice Sotomayor explained in her concurrence in Jones, “the trespassory test . . . reflects an irreducible constitutional minimum: When the government physically invades personal property to gather information, a search occurs. The reaffirmation of that principle suffices to decide this case.”²¹² This reasoning applies equally to aerial surveillance cases. When aerial surveillance can be analyzed under the test that this Note proposes, which will often be the case, courts can reach easy outcomes and avoid the difficulties of Katz altogether.

* J.D., May 2022, University of Michigan Law School. Thank you to Professor Evan Caminker for pushing me to make this Note as strong as possible. Thank you to Professors Eve Primus and David Moran, and to my friends, John Juenemann, Kacyn Fujii, and Matthew Guiang, for reading early drafts and providing valuable comments and critiques. Thank you to the Notes Editors of Volumes 121 and 122 for providing such helpful, thoughtful edits, and to the Editors of Volume 122 for carrying this Note to completion. Lastly, a big thank you to my parents, Faris and Nawal Khalil, for the countless sacrifices they’ve made over many years, which have enabled me to publish this piece today.