The Civil Aeronautics Authority, a predecessor of the FAA, claimed all airspace above 500 feet as public domain.
Notes on verification
Confirmed by primary Supreme Court text (US v. Causby, 328 U.S. 256) and independently corroborated by FAA history page, Cornell Law, Findlaw, and secondary legal commentary. Accurately paraphrases the daytime minimum safe altitude of 500 feet as the threshold for public domain airspace.
Sources
- How Much of the Sky Overhead Do You Own? (smithsonianmag.com)
- https://caselaw.findlaw.com/court/us-supreme-court/328/256.html (caselaw.findlaw.com)
- https://law.cornell.edu/supremecourt/text/328/256 (law.cornell.edu)
- https://www.faa.gov/about/history/brief_history (faa.gov)