Please remember something: God forbid there is ever an attack on a plane again and the attackers use something like a circular cutter disassembled as a weapon. As much as a pain in the butt as not being able to take certain items on a plane, just keep in mind, people with terrible motives may take those very same objects on as well. No one thought about box cutters prior to 8 years ago.
The reason you can’t take something such as a circular cutter on, but you can take circulars needles on, is that once you’ve been cut, in that instant, you’re done for, but if someone is choking you with a circular needle, another person can help you and you’ll survive. Not pleasant to discuss in a knitting forum, but that’s the answer to that question.
No matter what objects the TSA says is allowed, if the agent determines that YOUR object could pose a threat, it will be taken from you, and I would recommend not putting up a fight, as there will be consequences for that. Doesn’t matter that 1000 other knitters you know had no problem and that you’re flying from NYC to Albany. It the agents want to take them, they will. Period.
There is a kind of DPN needle called Comfort Zone, which are extremely flexible. I have taken them on international flights and showed the agents that they could be bent in half, and was allowed to take them on. You could hit an agent who will refuse to let you take them, but at $7 a set, it’s not the end of the world to have them taken from you. If you can use DPNs and knit socks or mittens or gloves, they are the least likely to be taken.
And please-- I’m sure there are knitters on this forum who if they didn’t know someone lost on 9/11, know someone who knows someone who did. (It’s hard to be on the east coast and not have been somehow touched by that terrible day.) Please be sensitive and avoid the “eye rolls” about how the airlines and TSA are trying to keep us safe.