I took my paper-piecing project with me on the plane to England this summer and had no problems with the sewing needles and pins going through security. Heathrow airport was very strict, too, we all had to take off our shoes and they were confiscating water bottles. For cutting thread, I had a box of dental floss in my toiletries bag - the little cutter on the dental floss box works great for thread - someone here gave me that tip!
You should double check the regulation son the website for the airline that you will be flying with, and/or the airport you will be flying from, but a small sewing kit is allowed under the current FAA security guidelines.
Jan