1. Nothing Al Qaeda tries will be caught the first time because it was designed around gaps in TSA security.
2. It is impossible to eliminate all gaps in airline security.
3. Airline security screening based on eliminating every vulnerability will therefore fail because it is impossible. But it will by necessity become increasingly onerous and invasive on the travelers.
E. Spriggs, F. De La Torre, and M. Hebert. 2009 IEEE Computer Society Conference on Computer Vision and Pattern Recognition Workshops, page 17-24. (June 2009)