Airspace & Fourth Amendment Expectations of Privacy

By | November 2, 2021

Some people wonder how much expectation of privacy there is when flying aircraft in the airspace of the United States. This cuts two ways: expectations of privacy of those persons (pilots and passengers) flying in their aircraft and expectations of homeowners on the ground being flown over.

Expectations of Privacy of Pilots

Many incorrectly assume that all aircraft must use transponders, transmit ADS-B Out, or make 2 way radio communications all over the place.  This is not true.  There are thousands of airports you can take off from without having to make radio transmissions and thousands and thousands of square miles of airspace you can fly in without a transponder or ADS-B out.  Let me explain.

Here is an FAA sectional chart for South Florida. I picked this area because it has a fair mix of Class D towered airports and also 3 major Bravo airports (Miami, Tampa, and Orlando). It’s not super busy like the up in the New England area but it isn’t sparse like the Midwest.  It was marked off according to 14 CFR Sections 91.126- 91.131, 91.215, and 91.225 assuming the flight is at 700ft above ground level. The reason for this is the regulations have different altitudes for when equipment is required.


Green = (~73% of Colored Airspace and ~23,475 Square Miles) No 2-Way Radios, No Transponder, and No ADS-B Out Required Below 700 feet above ground level.
Orange = (~2% of Colored Airspace and ~ 644 Square Miles) Only 2-Way Radios Required for Communications
Red = (~25% of Colored Airspace and~ 7841 Square Miles) Requires Transponder and ADS-B Out. 2-Way Radios Required for Some of the Airspace.

How I did the math is shown down below.

As you can see in green, there are large areas where you can take-off, fly, and land, without transmitting or identifying yourself. You can protect your privacy and fly an aircraft. A person flying around in navigable airspace does have a reasonable expectation of privacy at lower altitudes.

Once you go higher in altitude, or have equipment installed, things start to change and there are more reporting requirements because the higher you go, you are now interacting with the National Airspace System where aircraft under the control of ATC are flying. In these instances, transponders and certain ADS-B out equipment have the capability to broadcast anonymously but the location information is reported. At certain airports, you have to identify yourself and receive clearance to enter (Miami International for example).

There are a lot exceptions here and exceptions to the exceptions but what I’ve shown up above, there are ways privacy can be preserved when flying in navigable airspace but there are some locations where- in the interest of safety- identification and location data must be transmitted.

Privacy Expectations of Home Owners Regarding Overflights

I would argue that for certain portions of the United States, radar traffic data shows that it would also be reasonable for home owners on the ground to not expect overflying aircraft. One research report I read discussed FAA radar data showing for this remote portion out west, there was not one aircraft that flew over the area in an entire month!

In Florida v. Riley, the United States Supreme Court had to deal with whether a helicopter flying at 400ft was a search. Justice O’Connor concurred with the rule but provided different reasoning which I think is applicable for rarely flown areas:

Ciraolo involved observation of curtilage by officers flying in an airplane at an altitude of 1,000 feet. In evaluating whether this observation constituted a search for which a warrant was required, we acknowledged the importance of curtilage in Fourth Amendment doctrine: “The protection afforded the curtilage is essentially a protection of families and personal privacy in an area intimately linked to the home, both physically and psychologically, where privacy expectations are most heightened.” 476 U. S., at 212-213. Although the curtilage is an area to which the private activities 453*453 of the home extend, all police observation of the curtilage is not necessarily barred by the Fourth Amendment. As we observed: “The Fourth Amendment protection of the home has never been extended to require law enforcement officers to shield their eyes when passing by a home on public thoroughfares.” Id., at 213. In Ciraolo, we likened observation from a plane traveling in “public navigable airspace” at 1,000 feet to observation by police “passing by a home on public thoroughfares.” We held that “[i]n an age where private and commercial flight in the public airways is routine,” it is unreasonable to expect the curtilage to be constitutionally protected from aerial observation with the naked eye from an altitude of 1,000 feet. Id., at 215.

Ciraolo’s expectation of privacy was unreasonable not because the airplane was operating where it had a “right to be,” but because public air travel at 1,000 feet is a sufficiently routine part of modern life that it is unreasonable for persons on the ground to expect that their curtilage will not be observed from the air at that altitude. Although “helicopters are not bound by the lower limits of the navigable airspace allowed to other aircraft,” ante, at 451, there is no reason to assume that compliance with FAA regulations alone determines ” `whether the government’s intrusion infringes upon the personal and societal values protected by the Fourth Amendment.’ ” Ciraolo, supra, at 212 (quoting Oliver v. United States, 466 U. S. 170, 182-183 (1984)). Because the FAA has decided that helicopters can lawfully operate at virtually any altitude so long as they pose no safety hazard, it does not follow that the expectations of privacy “society is prepared to recognize as `reasonable’ ” simply mirror the FAA’s safety concerns.

Observations of curtilage from helicopters at very low altitudes are not perfectly analogous to ground-level observations from public roads or sidewalks. While in both cases the police may have a legal right to occupy the physical space from which their observations are made, the two situations 454*454 are not necessarily comparable in terms of whether expectations of privacy from such vantage points should be considered reasonable. Public roads, even those less traveled by, are clearly demarked public thoroughfares. Individuals who seek privacy can take precautions, tailored to the location of the road, to avoid disclosing private activities to those who pass by. They can build a tall fence, for example, and thus ensure private enjoyment of the curtilage without risking public observation from the road or sidewalk. If they do not take such precautions, they cannot reasonably expect privacy from public observation. In contrast, even individuals who have taken effective precautions to ensure against ground-level observations cannot block off all conceivable aerial views of their outdoor patios and yards without entirely giving up their enjoyment of those areas. To require individuals to completely cover and enclose their curtilage is to demand more than the “precautions customarily taken by those seeking privacy.” Rakas v. Illinois, 439 U. S. 128, 152 (1978) (Powell, J., concurring). The fact that a helicopter could conceivably observe the curtilage at virtually any altitude or angle, without violating FAA regulations, does not in itself mean that an individual has no reasonable expectation of privacy from such observation.

In determining whether Riley had a reasonable expectation of privacy from aerial observation, the relevant inquiry after Ciraolo is not whether the helicopter was where it had a right to be under FAA regulations. Rather, consistent with Katz, we must ask whether the helicopter was in the public airways at an altitude at which members of the public travel with sufficient regularity that Riley’s expectation of privacy from aerial observation was not “one that society is prepared to recognize as `reasonable.’ ” Katz, supra, at 361. Thus, in determining ” `whether the government’s intrusion infringes upon the personal and societal values protected by the Fourth Amendment,’ ” Ciraolo, supra, at 212 (quoting Oliver, supra, at 182-183), it is not conclusive to observe, 455*455 as the plurality does, 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.” Ante, at 451. Nor is it conclusive that police helicopters may often fly at 400 feet. If the public rarely, if ever, travels overhead at such altitudes, the observation cannot be said to be from a vantage point generally used by the public and Riley cannot be said to have “knowingly expose[d]” his greenhouse to public view. However, if the public can generally be expected to travel over residential backyards at an altitude of 400 feet, Riley cannot reasonably expect his curtilage to be free from such aerial observation. . . . 

Because there is reason to believe that there is considerable public use of airspace at altitudes of 400 feet and above, and because Riley introduced no evidence to the contrary before the Florida courts, I conclude that Riley’s expectation that his curtilage was protected from naked-eye aerial observation from that altitude was not a reasonable one. However, public use of altitudes lower than that — particularly public observations from helicopters circling over the curtilage of a home — may be sufficiently rare that police surveillance from such altitudes would violate reasonable expectations of privacy, despite compliance with FAA air safety regulations.

In a remote location, you could maybe argue traffic is really rare. It’s worth a shot.


Here is how the math worked out.

Airport Size in sq miles
Total Green (includes Orange and 2 Reds) 24928 Green
PGD 76 Orange
APF 65.2 Orange
BCT & PMP 95 Orange
Gwinn 67.3 Orange
SUA 59.4 Orange
FPR 69.6 Orange
LAL 20.3 Orange
Bartow 57 Orange
VRB 71.8 Orange
MLB 62.3 Orange
MIA 3686 RED
TMP 2414 RED
Percent of Total
Green Airspace 23475 0.73
Red 7841 0.25
Orange 644 0.02
Sum of Colored Airspace 31960 1