Does a passenger need to board a plane before a customs stop?

6 Appellant also contends that the border search exception is inapplicable here because the search did not take place at the "functional equivalent" of the border. See Almeida-Sanchez v. United States, 413 U.S. 266, 273, 93 S.Ct. 2535, 2539, 37 L.Ed.2d 596 (1973). In United States v. Duncan, 693 F.2d 971, 977 (1982), cert. denied, 461 U.S. 961, 103 S.Ct. 2436, 77 L.Ed.2d 1321 (1983), however, we held that it would be "unreasonable" to require that a passenger board a plane before allowing a customs stop. "It is enough that the passenger manifests a definite commitment to leave the United States and that the search occur in reasonable temporal and spatial proximity to the departure." Id.