The Ninth Circuit makes clear, in a 15-judge en banc decision, that airport searches are constitutionally justified as "special needs" searches because they are generally reasonable and aimed at more than just normal law enforcement, and not because of some (fictional) implied consent on the part of passengers. This has legal consequences:

We have held that airport screening searches, like the one at issue here, are constitutionally reasonable administrative searches because they are "conducted as part of a general regulatory scheme in furtherance of an administrative purpose, namely, to prevent the carrying of weapons or explosives aboard aircraft, and thereby to prevent hijackings." Our case law, however, has erroneously suggested that the reasonableness of airport screening searches is dependent upon consent, either ongoing consent or irrevocable implied consent.

The constitutionality of an airport screening search, however, does not depend on consent, and requiring that a potential passenger be allowed to revoke consent to an ongoing airport security search makes little sense in a post-9/11 world. Such a rule would afford terrorists multiple opportunities to attempt to penetrate airport security by "electing not to fly" on the cusp of detection until a vulnerable portal is found. This rule would also allow terrorists a low-cost method of detecting systematic vulnerabilities in airport security, knowledge that could be extremely valuable in planning future attacks.

Thanks to How Appealing for the pointer.