At the time the FAA permitted 4" blades in the cabin. Once through the metal detector, what ever is in your carry on you are free to place on your body. The dudes on security follow FAA policy, not airlines. A 2001 X-ray machine, if available, would need to detect then. Unlike now, airport X-ray scanners then were pretty primitive; think of the junky things you see board hotel staff pretend to look at in Indian hotels. In a bag full of stuff, the operator isn't going to spot them. These days, the system differentiates between material types, and applies a pseudo-colour for the operator, ie telling what's metal and what's organic. Back then, it was just a black and white image. Even if they did spot basically a craft knife, guess what, under the rules of the time, no problem. Most passengers back then walked through the metal detectors with pockets a jangling with change, keys, maybe even that Supertool on your belt. In 2001, only about 5 airports had the back scatter machines, and nothing like today. Its easy to forget how things have changed.
