United States. Government Accountability Office. Aviation Security: TSA Has Strengthened Efforts to Plan for the Optimal Deployment of Checked Baggage Screening Systems, but Funding Uncertainties Remain, text, June 29, 2006; (https://digital.library.unt.edu/ark:/67531/metadc295118/m1/1/: accessed December 9, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .