US v. Causby: Airspace Rights, the Ad Coelum Rule, and Drones

United States v. Causby is the 1946 Supreme Court decision that scrapped the old rule giving landowners the sky above their property “to the heavens” and replaced it with a narrower but constitutionally protected right in the airspace immediately above the ground. The Court ruled that when military aircraft flew as low as 83 feet over Thomas Lee Causby’s North Carolina chicken farm, destroying his business and making the property nearly unlivable, the federal government had taken a flight easement across his land and owed just compensation under the Fifth Amendment.¹

The Chicken Farm Under the Glide Path

Thomas Lee Causby and his wife owned 2.8 acres near the Greensboro-High Point Municipal Airport in North Carolina. During World War II, the federal government leased the airport for heavy training operations. The northwest-southeast runway ended about 2,220 feet from the Causbys’ barn and 2,275 feet from their house, and the required glide path sent bombers, transport planes, and fighters directly over the property at 83 feet — clearing the house by 67 feet, the barn by 63 feet, and the tallest tree by 18 feet.¹

The effect on the farm was devastating. The noise was startling. Landing lights turned the property into daylight at night. Chickens panicked and flew into walls; roughly 150 birds killed themselves that way, six to ten on some days. Egg production collapsed, and the commercial poultry operation ended. The Causbys lost sleep, lived in constant anxiety, and feared a plane would crash into the house.²

They sued in the Court of Claims, which found the government had taken an easement effective June 1, 1942, and awarded $2,000. The government appealed, and the Supreme Court took the case.

The Old Rule: Ownership to the Heavens

For centuries, Anglo-American property law followed the Latin maxim cuius est solum, eius est usque ad coelum et ad inferos: whoever owns the soil owns everything above it up to the sky and below it to the center of the earth. Under that rule, any unauthorized entry into the airspace above your land was trespass, no different in principle from someone walking across your field.

Aviation made that untenable. If every landowner truly controlled the sky above their property to infinite altitude, every commercial flight would be a mass trespass. Congress addressed the problem in the Air Commerce Act of 1926 by declaring navigable airspace above certain minimum altitudes to be part of the public domain, open to a public right of transit. The higher atmosphere became a public highway. What Causby forced the Court to decide was what happened in the gap between the ground and that highway, especially when military flights dipped far below normal safe altitudes.

What the Supreme Court Held

Justice William O. Douglas wrote for the majority. He acknowledged that the ancient doctrine of ownership to the heavens “has no place in the modern world.” But he rejected the government’s argument that declaring airspace public left landowners with no protected interest in the air near the surface. A landowner, Douglas wrote, “owns at least as much of the space above the ground as he can occupy or use in connection with the land.” The Court called this zone the “immediate reaches” above the property: the space where buildings stand, trees grow, and daily life takes place.²

The Fifth Amendment forbids private property being “taken for public use, without just compensation.” Flights so low and so frequent as to be a “direct and immediate interference with the enjoyment and use of the land,” Douglas wrote, “are as much an appropriation of the use of the land as a more conventional entry upon it.” The evidence showed exactly that: the overflights had imposed a de facto flight easement across the Causbys’ land.¹

This was not ordinary eminent domain, where the government files proceedings and pays before taking control. The government had simply begun flying and left the Causbys to sue. When an owner has to go to court to demand payment after the government has already damaged or appropriated the property, that process is called inverse condemnation. The Court agreed the government owed compensation, but reversed the $2,000 award and sent the case back to the Court of Claims for more detailed findings on the nature and duration of the easement.

Justice Black’s Dissent

Justice Hugo Black dissented; Justice Robert Jackson took no part. Black viewed the Causbys’ situation as a nuisance claim, not a constitutional taking. The noise and glare caused real harm, he agreed, but the proper remedy was a suit for damages, not a finding that the government had seized a property interest.³

He also worried about the future. Congress, he wrote, had declared the air “free, not subject to private ownership, and not subject to delimitation by the courts.” By recognizing landowner rights in low-altitude airspace, the majority was building constitutional barriers around a domain Black thought Congress and federal regulators were meant to control in full.³

Where the Airspace Line Sits Today

Causby drew a line between two zones without picking a number. Above some altitude, the air belongs to the public, controlled by federal regulators and open to transit. Below that altitude, in the “immediate reaches” of the land, the property owner holds a protected interest. The Court deliberately declined to fix the boundary, noting only that airspace “apart from the immediate reaches above the land, is part of the public domain.”²

Federal statute fills part of the picture. Under 49 U.S.C. § 40103, the United States holds exclusive sovereignty over the nation’s airspace, and every citizen has a “public right of transit through the navigable airspace,” with the FAA Administrator setting the rules for safe altitudes and flight patterns.⁴

The FAA’s current minimum safe altitude rules under 14 CFR § 91.119 set the floors:

Over congested areas: 1,000 feet above the highest obstacle within a 2,000-foot horizontal radius.
Over non-congested areas: 500 feet above the surface.
Over open water or sparsely populated areas: no closer than 500 feet to any person, vessel, vehicle, or structure.

Aircraft operating below those thresholds — mostly during takeoff and landing near airports — sit in the uncertain zone where Causby‘s protections do the most work. Because the Court refused to name a fixed altitude, each case turns on how the flights actually affect the landowner’s use of the property, not on whether an aircraft crossed a numerical line.⁵

Civilian Airports and Drones

Causby involved military flights, so the federal government was the obvious defendant. Sixteen years later, in Griggs v. Allegheny County (1962), the Supreme Court answered the civilian version of the question. A county that owns and operates an airport bears the liability when its required flight paths send aircraft repeatedly over private homes at low altitude. The airport operator, not the federal government, owes just compensation, even when the flight paths conform to federal regulations.⁶

The newer frontier is drones. Commercial and recreational unmanned aircraft routinely operate at 100 to 400 feet — squarely inside the zone Causby identified as the “immediate reaches.” Neither Congress nor the FAA has drawn a clear line between the landowner’s protected airspace and the navigable airspace open to drone operators, and legal commentators have flagged low-altitude drone trespass as ripe for litigation. Until a clearer boundary emerges, every persistent low-altitude drone operation over private land raises the same question the Causbys brought to the Supreme Court in 1946: at what point does using someone’s airspace become taking their property?

1
Supreme Court of the United States. United States v. Causby
2
Justia. United States v. Causby
3
Loc. United States v. Causby, 328 U.S. 256 (1946)
4
Office of the Law Revision Counsel. 49 USC 40103 – Sovereignty and Use of Airspace
5
eCFR. Minimum Safe Altitudes: General (FAR 91.119)
6
Justia U.S. Supreme Court Center. Griggs v. Allegheny County