The general concensous seems to be the following:
- No fixed blades
- Folders under 4" blade length
- No serations
- No "mean looking" blades. What does this mean? Who knows. I would avoid black coatings and geometrical blade shapes personally. YMMV
As mentioned above, there are times that you MAY get away with a few things, but it's probably not worth the hassle. I've carried a small Sebenza and a mini-SOCOM on board planes. Both have plain edges, are about 3" in blade length, and have silver finishes. I put them in my carry-on suitcase in the little toiletries bag that contains deoderant, shampoo, toothpaste, etc... I position the knife in the bag so that when I lay the bag on the x-ray belt it sees the smallest knife profile possible. I try to position it so that the operator sees only the butt-end of the knife. I've never had any problems when doing this. No bag searches, etc... Even if they did a search, the blade seems to fit all of the required criteria, so they can't say much. As mentioned above, I do carry a small padded, self-addressed, postage paid (remember to use enough postage) envelope with me just in case...
Kelly