The following excerpt is from U.S. v. Groomer, 596 F.2d 356 (9th Cir. 1979):
Groomer also contends his arrest was unlawful because the officers failed to knock on the door or announce their presence before entering the hangar. Although entry into a private residence or office may require notice (United States v. Phillips, 497 F.2d 1131 (CA 9 1974); 18 U.S.C. 3109), the hangar was not a private place, and under the circumstances, the officers were justified in believing announcement of their presence might impede the arrest.
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