Just an FYI, I traveled through LAX and JFK last week with my knitting (on 13" plastic needles) and the screeners didn't bat an eye.
I had the TSA guidelines printed as back up and was prepared to check my bag if there were any problems.
(Don't tell, but I also had a tiny seam ripper to cut the yarn. I'm such a rebel!
So, boys and girls, don't be afraid to take your project on your next flight!