This comes up a lot around here. I’ll tell you my advice, and my opinion:
The TSA says that you can take them in carry-on. However, it’s up to the agent in the moment, and if the one you get just saw that episode, or just had a cousin who fell on her needles and ended up in the ER, you can be assured they will not let you take them on. They are supposed to make case by case judgments, and they are supposed to shake things up constantly, so that no one really knows what to expect is accetable or not. I know this is a pain, but it keeps us all safe. No one thought about explosive in shoes until a few years ago, and now we all take our shoes off. Not convenient? Neither is getting blown to bits on that flight you’re taking to visit your sister in Boston.
On long flights, knitting feels like a preserver of sanity, but again, do you want to feel stir crazy for 10 hours, or live to see the next day? What everyone forgets, it that it’s not just you with the needles, it’s the person with the needles with the bad intentions. I would never think of using a steak knife to cut anything other than steak. There are people who think otherwise.
There are likely some variables-- such as the type of needles. Comfort Zone makes some very bendable hylon DPNs which should be the least problematic, and 14" metal straights are probably the most problematic. Also, you’re most likely to be allowed them on a short domestic flight, and least likely on a long international flight, especially to the Middle East. But no matter what, you are taking your chances of getting them taken away. People talk about mailing them back to yourself, but in my airport, the mailboxes are only located in the hallways near the seating areas for the gates, that is, AFTER security. In other words, if they take your needles, you can consider them gone. Remember how many people want to get something important to them through security, and how much time the agents have to deal with it.
My pet peeve is when postings like this go up, you’ll always get several people saying how they got their needles through without a problem. It doesn’t matter. There may be 1000 people who get theirs through, but you get yours taken away. You might eat 100 unwashed apples without getting sick. Does that mean you won’t get sick on the 101st? Nope.
The TSA folks are trying to keep us all alive. I think we can put down our knitting for a few hours to make that happen.