Here’s an interesting (to me, at least) trade secret case involving restoration of antique aircraft. Brent Taylor purchased the carcass of an F-45, a 1930s era aircraft and wanted to accurately restore it so that it was once again airworthy, and could fly. He sought from the Federal Aviation Administration (FAA) the ‘Type Certificate” for this aircraft. Type Certificates are the imprimatur issued by the FAA upon review of design specifications and other materials. The FAA claimed that in this instance the Type Certificate files were trade secrets of Fairchild. Trade secrets are exempt from FOIA requests. It’s taken 8 years, including a review by the Supreme Court, to get the materials released.
See Taylor v. J. Randoph Babbitt, https://ecf.dcd.uscourts.gov/cgi-bin/show_public_doc?2003cv0173-77